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Establishing Transplanted Trees: Water You Going To Do? By Rich Hauer
Reprinted from the Minnesota Shade Tree Advocate volume 3 number 3. Healthy trees that mature into legacies do not happen by chance. Ask city foresters and they may say you need to match trees that are biologically adapted to a site. Hopefully you will also find trees (they're in short supply these days) for the site. Ideally, delivered trees must then be inspected to monitor for compliance with tree specifications (i.e., depth to the root system, pests, stem condition) included as part of the bid proposal. Short tree planting seasons are sometimes a barrier. Further, at times poor soil characteristics (e.g., organic matter, pH, aeration, drainage) at the site need modification. After these hurdles are cleared you still have to plant the tree. But does the job end there?
We can see the scorching in this maple's leaves, a symptom of stress from inadequate watering. But the impact on overall vitality and delay in establishment may not be as obvious.
For some planting programs, the project ends after planting. For others, trees are periodically watered when maintenance staff are not mowing turf. Others may be more dedicated and water trees weekly. All these scenarios will work during years when rainfall is frequent and plentiful. During normal years, however, even weekly watering of newly transplanted trees may not be enough. When establishing trees are subjected to water deficits, growth and function of the leaves, shoots and root growth slows to negligible levels. This delays establishment and may even lead to the death of these parts. In the worst case scenario, which too often needlessly happens, a net decrease in living biomass occurs and the canopy becomes smaller. The tree canopy may now resemble a 1-inch caliper tree rather than the planted 2- inch caliper tree. The purpose of this article is to shed light on recent scientific-based prescriptions for watering trees to aid establishment.
Water and Tree Physiology The function and growth of plants as suggested by Justus Von Liebig in 1840 (modified later by others) is limited by the factor present in the smallest amount relative to its minimum requirement. Ample light, water, oxygen, carbon dioxide, mineral nutrients and suitable temperatures are all important for plant growth and function. Quite often, how-ever, plant nutrients (e.g., nitrogen, phosphorus, potassium) are most commonly thought of as factors that limit plant growth. While these along with other nutrients are vital for growing healthy trees, water is the factor that most often limits growth. In humid regions, water accounts for approximately 80% of the variation in diameter growth. In arid regions, water accounts for approximately 90%. For the most part, trees can only take up water from soil in proximity to roots. Established trees are in contact with greater volumes of soil due to wide-spreading root systems, and are more capable of
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Minnesota Tree Care Advisors obtaining water. Newly transplanted trees have less soil volumes to extract water. Obviously, trees that have root systems severed to facilitate transplanting (i.e., bare root, balled & burlapped and tree spade) have fewer roots and a smaller soil volume in contact with roots. Containerraised trees also have a small root area to obtain water even though they are transplanted with the majority of their root system intact. In fact, newly planted container-grown trees require daily watering the first few weeks following transplanting. Just ask a nursery operator how often they water their containerized trees!
After planting, form a berm with mulch at the edge of the root system to insure water is placed in proximity to their roots.
Is There a Way to Reduce Water Requirements of Newly Transplanted Trees? The removal of branches at transplanting, or compensatory pruning, was a common practice in the past. The idea was simple: since roots were removed during the transplanting operation, then the canopy should be pruned accordingly to compensate for the root loss. It was thought that fewer branches and leaves meant less demand for water, leading to better establishment. Research from Oklahoma, Colorado and England have found trees establish more quickly without compensatory pruning when watered frequently. With little rainfall or supplemental irrigation, trees pruned and unpruned at planting establish similarly (See Pruning at Planting, MNSTAC Advocate, Spring 1999. Antitranspirants (also known as antidesiceants) have also been suggested to aid transplant success. Antitranspirants reduce water loss through stomates by either causing stomate closure or covering stomates with a waxy film that is a barrier to water loss. In theory antitranspirants seem reasonable, but in practice they may lengthen the establishment period. While closed or blocked stomates reduce water loss, they also decrease carbon dioxide entry into leaves. Less carbon dioxide accordingly reduces the manufacture of energy compounds from photosynthesis. But what practices can be used to reduce water requirements of transplanted trees? Two methods are mulching trees (See Mulching, MNSTAC Advocate, Spring 1999) and planting smaller-sized trees. Mulch helps reduce evaporation from soil surfaces and also adds organic matter to the soil. Smaller trees establish sooner than larger trees and require less water during watering. In addition, a berm can be formed at the edge of the root system to insure applied water is placed in proximity to the roots.
Prescription or Dosage-Based Watering Historically, tree-watering guidelines have suggested watering trees every seven to ten days with 1 to 1-1/2 inches of water. While this frequency and amount of water may work in some situations, research within the last five years from the Morton Arboretum and the University of Florida at Gainesville suggests more frequent watering is necessary for optimal tree establishment. Within two to three days, rootballs of newly planted trees will dry to levels that impede root growth. Newly transplanted trees in the Midwest will benefit from daily watering for the first one to two weeks, applying approximately 1 to 1-1/2 gallons per-stem-caliper inch per watering. Thereafter, water trees every two to three days for the next two to three months and then weekly at the same rate until established. Remember, newly transplanted trees are absorbing water from a diminished rooting area (i.e., apply water to the root ball). Roots must generate and grow into surrounding soils before a larger soil volume can be tapped for moisture. Tree roots grow approximately 18 inches
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Minnesota Tree Care Advisors in length annually in the Midwest. Trees in Minnesota will become established within one to one-and-a-half years for each caliper inch of stem. Thus, it takes two to three years before a 2-inch caliper tree is established. The more closely you match your watering frequency to the optimum the quicker trees become established. Labor to water trees is sometimes given as a reason or excuse for not adequately watering newly planted trees. If the water requirements of newly transplanted trees cannot be met, planting smaller trees is recommended. For example, 1- and 2-inch caliper trees have less root loss and recover faster than trees 2 to 3 inches in stem caliper. Mulching trees to a 2- to 3-inch depth is recommended as it helps reduce evaporation and conserve precious water. Incorporating the labor cost of watering trees within the tree planting budget should insure adequate watering occurs and trees establish successfully. If tree planting is part of the contract process, consider including watering as an additional component in the bid. Your community forestry program will be far better off if trees are adequately watered rather than if you are continually replanting and not realizing the benefits that mature and established trees provide.
Irrigation Guidelines for Quickly Establishing Trees (Well-drained sites during the growing season in the Midwest) Less than 2-inch caliper planting stock Water daily for 1 week; every other day for 1 to 2 months; weekly until established 2- to 4-inch caliper planting stockWater daily for 1 to 2 weeks; every other day for 2 months; weekly until established 4-inch caliper planting stockWater daily for 2 weeks; every other day for 3 months; weekly until established Notes Modified from Gilman, E.F. 1997. Trees for Urban and Suburban Landscapes. Delmar Publishers. 662 pp. Delete daily irrigation when planting in fall or early spring. Little irrigation is needed when planting in winter. Reduce frequency in cool, cloudy, wet weather if soil is poorly drained (soil drains less than 3/4 inches per hour). Eliminate daily irrigation in poorly drained soil. Following a rainfall, wait until all free moisture drains out of the soil. Establishment takes 12 months per-inch- trunk caliper. Minimum frequency for survival could be once each week. Irrigation can cease once trees drop deciduous foliage in the fall. At each irrigation, apply 1 to 1.5 gallons for each inch of trunk diameter to the root ball. Rich Hauer is a Professor at University of Wisconsin-Stevens Point: College of Natural Resources
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"We Guarantee Our Trees For A Year." Is That Enough? By Gary Johnson and Andy Sobert
Reprinted from the Minnesota Shade Tree Advocate, volume 3 number 4. Our "disposable, costs- too-much-to-repair, junk it" way of living has permeated our lifestyle and has influenced our way of thinking regarding tree selection, planting and care in our urban landscaping. We tend to have the attitude that says, "Plant it now; if it doesn't survive, we'll replace it." This attitude is fostered by warranties of garden centers, nurseries and other firms supplying trees to the homeowner. "Guaranteed for One Year" is a common warranty offered by tree and shrub suppliers. Most forestry professionals will agree that, even under very adverse conditions and with minimal care, most trees will "survive" for twelve months. As urban forestry professionals and advocates, we need to expand the thinking and the expectations of tree buyers who are offered a warranty of 365 days. Trees should be viewed as permanent structures, especially when put in the perspective of their potential lifetimes. An exercise in humility for all of us might include the estimated longevity or years to maturity for these selected trees*: Sequoia - 4000-5000 years Red pine - 350 years Eastern larch - 100-200 years Bur oak - 600 years White spruce - 250-300 years Bur oaks can live over 250 years in Minnesota.
Purchasing quality plants vs. purchasing guarantees At the heart of the issue is the assumption of risk, and the risk in this issue is whether or not the purchased trees are healthy enough to potentially live long, useful lives in our landscapes. Dick Cross of Cross Wholesale Nurseries, Inc., in Lakeville, MN, offered this grower's perspective of one-year guarantees: If the tree has the potential to survive (adequate roots, leaves, stored energy), then the guarantee is adequate. In other words, if the tree hasn't been grown well and harvested correctly, it is likely to fail within that first year and the guarantee is a worthy investment. The retailer assumes that risk for the first year of the tree's life. According to Cross, the consumer should examine the trees before purchasing them and look for evidence that the tree has been grown and cared for properly. This includes good foliage, intact and healthy bark, good over-all vitality if the tree is containerized, a moist, full, and intact (minimum of broken roots) root system if the tree is bare-
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Minnesota Tree Care Advisors rooted, and in general, a 50/50 canopy/stem ratio. For instance, a 10foot tall tree should have the branches starting at about 4.5-5 feet above ground. Based on the research conducted at the University of Minnesota, Forest Resources Department since 1994, the depth to the first main order roots (first true branch roots) is equally if not more important to long term health. Diagnostic root collar excavations and randomized sampling of three tree species (ash, linden, maple) have revealed that buried root systems often result in shorter lives for trees. This is a concern when purchasing containerized and balled-and-burlapped trees, situations where you can't see the roots. When purchasing these plants, ask the retailer for permission, to probe down through the soil ball with a wire (coat hanger gauge) to find the depth to the first branch roots. If the roots are close to the surface, that's good. If they are deeper than four inches from the surface of the soil/root ball, you will be purchasing an inferior root system, especially after you remove that excess soil at planting time.
Guarantees connected to installations Although many guarantees are tied to cash-and-carry purchases, many are also connected to installed landscapes. In these cases, the consumer purchases not only the tree but the contract to have itinstalled. Now the risk is not just whether or not the tree is healthy, but also whether it is handled and planted correctly. From his experience, Dick Cross believes the way trees are handled prior to planting, the way the planting sites and holes are prepared and the way trees are finally planted on the, site are all at least as important as the quality of the plant. Therefore, poor handling and planting techniques can lessen the chances of survival for a healthy tree in that first year. The error of placing the root (trunk) collar area several inches below the landscape grade often results in a condition known as stem girdling root syndrome, or a general slow decline in health, Unfortunately, based on the research conducted by the Forest Resources Department, these problems and subsequent decline often take 12-20 years to become obvious ... long after the one-year guarantee. The trees were healthy, but the handling and planting techniques placed the trees at risk for several years. Marc Shippee, City Forester for Blaine, MN, has encountered problems with some retail nurseries installing trees on new residential sites, in situations where the installed trees are mandated by the city's reforestation plans. One retail nursery in particular not only refused to pay careful attention to planting depth; they claimed that they've never had any problems with planting depth causing tree decline in the 1O year history of their business. Still, they threatened to void the guarantee on the trees if the homeowners or city forester insisted that the top half of the burlap, strings and wire baskets be removed. Shippee has taken the position of ensuring long-term health by insisting that these best planting practices be implemented (proper depth, removal of burlap, strings and wire), and has advocated that homeowners insist the one-year guarantee be honored. Will replacement trees fare better than the original guaranteed trees? Possibly not, unless some of the serious conditions that caused the failure of the original trees are remedied. If the cause of failure was a poor tree, then the replacement tree may do much better (if it's a good one). If the cause was chronically poor handling practices or site
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Minnesota Tree Care Advisors conditions, the new tree probably won't live long either. To fortify the plant guarantee when the plants are also being installed by a retail company, a consumer may want to develop a detailed contract between himself or herself and the company. Barb Kirkpatrick of North Oaks, MN protected her landscape investment by adding some details to the original contract offered to her. She specified that all trees and shrubs, must have their first, main order roots within one inch of the soil surface. As the work progressed on the project, she had to ask the installation contractor on two occasions to add the planting depth requirement before she would sign the contracts. Whether this oversight was an accident or purposeful, the example stresses the need for monitoring and double-checking on the part of the consumer. Did Kirkpatrick's contract clause protect her trees? After they were installed, she randomly checked a few plants to make sure they were planted correctly. They weren't. In the end, the original contractor took care of a few of the problems, extended the guarantee to two years, and just gave up on others. Kirkpatrick had the remaining trees correctly planted and has since used a different contractor for her expanding landscape. The new contractor told her "I want to plant legacies instead of just planting trees," and has abided by the clauses she has inserted in their contracts. In summary, Kirkpatrick recommends the following steps when contracting out tree planting on your own property. You'll better ensure not only the health of the trees, but the handling and planting practices:
1. Communicate your expectations with the contractor. 2. Be specific when drawing up the contract and double check that all of your conditions are included before signing it. 3. Withhold 50% of the contract balance until you are satisfied that the contract has been honored. 4. Perform a random inspection of the installed trees and shrubs before the final payment. 5. Hire reputable, qualified and ethical people who care about their reputation.
As Dick Cross also recommended: If you notice a tree is not performing well, don't wait until the end of the guarantee period and expect a free replacement. Call the retailer or contractor as soon as you notice problems because they may be able to intervene and save the tree. Buyers must be educated to look past the "One Year Guarantee." They can expect much better results if they learn and adopt proven tree selection and installation practices, and assume some of the risks involved in creating arboreal legacies.
Gary Johnson is Associate Professor of Urban and Community Forestry,
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Minnesota Tree Care Advisors University of Minnesota, Department of Forest Resources. Andy Sobert is a Minnesota Tree Care Advisor and Member of the MNSTAC Research and Education Committee. *(Richard J Preston, Jr.; North American Trees, Fourth Edition)
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Fact or Fallacy: "Containerized Trees Are Fool-Proof Trees" By Gary Johnson
Reprinted from the Minnesota Shade Tree Advocate, volume 3 number 2. Containerized trees and shrubs began to enter most Midwestern garden centers in the 1960's, offering the potential for extending retail sales and landscape installations beyond the traditional spring and autumn seasons. They also "promised" that transplant shock would be all but eliminated, especially as compared to balled-in- burlap (B&B) or bare-rooted (BR), field-transplanted trees and shrubs. In the past four decades, growers have learned and relearned more about producing plants in containers. They've designed and modified the container sizes and, shapes, and are now marketing more trees in containers than ever before. But have containerized trees proven to be the green industry panacea for all seasonal, transplant shock and plant health problems?
MYTH: "Containerized trees have 100% of their original root systems because they have been grown in containers all of their lives." Unfortunately, this statement is not necessarily true. Some containerized trees are truly container-grown, from small seedlings or cuttings to landscape sizes, and do have almost all of their original roots in the containers. Some are field-grown, dug as bare- rooted trees and then potted up to be "finished-off." Some containerized trees may have been in those large containers for only 3-4 months before they are displayed in the retail nursery sales lot. They may have an adequate root system or they may not have much beyond those roots that were left on the trees when they were dug from the fields. And some trees and shrubs are field-potted, that is, dug from the nursery fields, potted with the same field soil and shipped to garden centers. So, containerized trees may or may not have a better root system than B&B or BR trees.
MYTH: "Containerized trees do not suffer transplant shock when planted in the landscape." Most of the transplant shock (reduced health, characterized by small leaves, chronic wilting, stunted growth, etc.) associated with B&B and BR trees is due to root losses during the transplanting operations. Even if containerized trees have adequate root systems for normal growth, they almost always suffer some sort of transplant shock as they leave the intensive care environment of the nursery, where they have received optimum amounts of water and nutrients. Most container "soils" are mixtures of materials that are optimum for root growth, holding the right amount of water but still well drained,
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Minnesota Tree Care Advisors and nutrient-rich. Many urban landscapes have compacted soils that are often poorly-drained and devoid of organic matter, and most landscapes are fully exposed to drying winds and full sun exposures. Unless the newly planted trees have been correctly planted, watered carefully every few days and the soil deficiencies were corrected before planting, these trees will also suffer transplant shock. Their roots were not removed during the transplanting operation, but they may die in the harsh environment of the typical urban landscape.
MYTH: "As opposed to B&B trees, containerized trees never have their first, main roots buried too deeply in the soil."
Figure 1. Remove excess soil over the main lateral roots.
Figure 2. make sure the depth of the planting hole is not any deeper than the distance between the root collar flare and the bottom of the container soil "ball."
Containerized trees are just as vulnerable to having their primary roots buried too deeply in the soil "ball" as B&B trees, and they need to be inspected for excess soil over the roots before planting. Probe down through the top of the container soil level with a coat hanger wire until you can feel the main lateral roots at the point where they are attached to the stem (root collar flare) (Figure 1). It is not unusual to find four or more inches of soil over those roots in containers. To avoid future problems that develop when trees are planted too deep, remove that excess soil and make certain that your planting hole is not too deep. These roots should be at or just below (1/2 to 1 inch) the landscape soil or mulch levels when planting is completed. So, the depth of the planting hole should be the distance between the root collar flare and the bottom of the container soil "ball" and not necessarily the depth of the entire soil "ball" (Figure 2). Containerized trees are convenient, less expensive than B&B trees, can be planted anytime the ground is not frozen and are usually easier to handle than B&B or BR trees. The production of trees in containers is a boon for the nursery and landscape industry, and they can be perfectly good trees. But they must be treated as any other tree: buy only those that you know have good root systems; understand that they need at least as much site preparation and care when planted in the typical landscape; and make certain that those first roots are at or near the soil surface when you finish the planting process. Your efforts will be rewarded with healthy, long-lived trees that are valuable additions to the landscape.
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The Right Way To Plant A Tree By Gary Johnson and Cindy Ash
Reprinted from the Minnesota Shade Tree Advocate, volume 1 number 1. Trees can be purchased in many sizes, as bare root, containerized or balled and burlapped specimens. Basic planting is the same but handling and special considerations apply, depending on the size and type. The inset picture shows the old way to plant a tree. The larger picture shows the new way to plant a tree: prepare a wide-diameter site and dig a properly sized hole in the center.
Tips for All Trees Select the right plantfor the site. Base this on the soil type, soil pH, surface and subsoil drainage, and exposure to sun, wind and de-icing salts. Prepare the site by removing the sod. Loosen the soil by tilling or spading an area three to five times wider in diameter than the width of the root system, and only to the depth of the root system. Dig a hole in the center of this circle that is one foot larger in diameter than the root ball and is exactly as deep. Maintain undisturbed (not loosened) soil beneath the root ball to prevent the tree from settling. Carefully place the tree in the center of the hole and doublecheck that the root collar (lowest part of the trunk, immediately above the uppermost root) is just above the top of the soil. Tip: The uppermost root should be just below the soil surface. See drawing for proper depth.
Backfill around the roots with the soil that was removed. Lightly pack or water the soil during this process to eliminate air pockets. Backfill to the height of the root ball, no higher. MULCH with four to six inches of coarse wood chips or shredded bark. Pull the mulch back from the trunk to prevent direct contact with the root collar and trunk. Water is very important to a newly planted tree. A slow, soilsaturating trickle a couple times a week is a good rule of thumb for a new tree, but varies depending on soil type and plant size. This should provide the new roots with sufficient moisture without
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Minnesota Tree Care Advisors drowning them. They need oxygen, too! Adjust the watering schedule accordingly for rain or very dry conditions. Don't Forget To Inspect containerized and container-grown trees prior to planting to see if the roots are pot boundcircling around themselves. (Avoid purchase of pot bound plants if possible). If pot bound, remove the pot and make a vertical slice up each quarter of the root ball to a depth of about one inch. Cut an X across the bottom of the soil ball to a depth of about one inch. Gently loosen some of the roots, then plant. Inspect bare root trees for broken roots and all trees for broken branches prior to planting. Remove any of these with a sharp hand pruner. Also, remove crossing or rubbing branches. Keep all types of root systems moist prior to planting. Moist straw or sawdust works well for bare root trees. Soak bare root trees in water one hour prior to planting. Sweat bare root trees in a shaded place such as a garage and keep them moist until the buds open. Sweating is a process that creates favorable conditions necessary for bud break and development on certain tree species, such as oaks and hackberries. Remove all containers prior to planting, including biodegradable, paper-mache pots. If the roots and soil are loose in the container, then place the container in the planting hole and carefully cut away the container as you backfill with soil. Be sure all roots extend away from the trunk to prevent future problems with encircling and stem girdling roots. Remove the upper two rungs on wire baskets before completely backfilling. Do not remove any of the wire basket before the tree is safely in the planting hole and is partially backfilled! Remove the nails holding the burlap together, then cut away the burlap after the plant has been partially backfilled. Never allow any burlap to remain above the soil surface. Cut and remove all twine and rope from around the soil ball after planting. Prevent animal damage to young trees by placing a cylinder of 1/4 inch mesh hardware cloth around the trunk, leaving two to three inches between the wire and the trunk.
Tips for Special Situations For heavy and/or poorly drained soils, plant slightly higher than normal and mound the soil up, to cover the roots. Do not add peat to poorly drained, clayey soils, as it can act as a
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sump and draw water into the root zone. Do not add rocks or gravel to the bottom of a planting hole to improve drainage-unless connected to drain tile. When using tree spades, water the trees thoroughly before moving them. Rough up the sides of the planting holes with a shovel or rake, then place the trees slightly higher than the original grade to allow for settling. If using a weed control barrier, use a porous landscape fabric. Do not use plastic around trees. Staking: Generally not necessary but if the tree is unstable should be applied to allow for some movement and the REMOVED within one year. Connect the tree to the stakes with wide (two inches or wider), flexile materials, such as strips of burlap, canvas or old bicycle inner tubes. Avoid ropes, strings or wires in garden hose sections.
Know Your Soils Test the soil for pH and nutrients. Contact your local Extension office. * Test the soil for drainage. Dig a hole 24" deep, and fill it with water. All water should drain within 24 hours. * Test the soil for compaction. You should be able to easily dig down two spade depths (about 18"). If the soil is too hard to dig, either don't plant there, or loosen the soil in an area with a diameter of ten feet. Gary R. Johnson is Professor of Urban and Community Forestry at the University of Minnesota, Department of Forest Resources. Cindy Ash is with the United States Forest Service. Specification graphics modified or taken from "Inspection and Contract Administration Guidelines for Mn/DOT Landscape Projects, 1997 Edition," except as noted.
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Effects of Deep Planting on Long-Term Tree Health By Gary Johnson
Tree roots need oxygen and water in order to survive and grow. Because of those basic requirements, the majority of tree and shrub roots grow in the upper 3 feet of most soils. And specifically, the majority of fine roots - those roots that absorb more than 90% of the water and minerals required for plant growth - usually grow in the upper 12 inches of most soils. In soils that are low in soil oxygen compacted clayey soils or water-soaked soils - all roots may be confined to the upper few inches, rarely penetrating deeper than a couple of feet. When the roots of trees and shrubs are buried too deep, their health and condition are often affected over time, and sometimes immediately. Health refers to their growth rate, leaf color, ability to recover from diseases and damage, and ability to withstand our harsh winters. Condition refers to their structural integrity: sound stem wood that is free of decay, cracks or weak points; supportive root systems, and canopies that are free of large amounts of dead wood. A properly planted or established tree or shrub normally will have the root collar flare at or slightly below the soil or mulch level. The root collar flare is the transition area between stem wood and the first, main order roots. In natural plantings, the root collar flare is clearly visible above the soil line, or may be slightly covered by leaf litter. When root systems are buried, less soil oxygen and water is available to the roots, and the roots must grow closer to the surface where there usually is a more reliable source of both. The energy that a newly transplanted tree or shrub must use to grow new roots and develop a normal, expanded root system must be used to grow upward before it can grow in a normal outward direction. Some, maybe many plants survive this burial and live normal lives after developing a normal root system. Others begin a long, slow decline of health and condition, and either die prematurely or fail suddenly during wind or ice storms. Often these plants die of secondary problems, not directly related to the dysfunctional root system. If root systems are abnormal, the health of the plant is stressed or strained to a point that the plant becomes abnormally vulnerable to common site stresses. Whereas healthy plants can survive most periodic droughts or defoliation due to insects, stressed plants may die from the additional stresses placed on them. Research conducted in the Forest Resources Department at the University of Minnesota has revealed that buried root systems of street trees is alarmingly common. In two randomized studies, it was found that the main order roots of sugar maples, green ash, and lindens were buried with 1-11 inches of soil (total number sampled was 302). When the trees were then condition rated (a numerical evaluation of the condition of the stems, canopies and foliage), there was a direct relationship between declining tree condition and depth of
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Minnesota Tree Care Advisors soil over the roots. In other words, as main order roots were covered by more and more inches of soil, the condition of all three tree species further declined. In addition to the decline in health and condition of trees, burying root collar flares may create another adverse condition. As root collar flares are increasingly buried, more of the stem tissue is buried and out of sight. A condition termed stem-girdling roots often develops in this stem-buried situation. Roots that have grown up toward the soil surface often wrap around or run close to the buried stems. As these roots enlarge over the years, along with the normal enlargement of the buried stems, the roots begin to compress and weaken the stem tissues. This creates a weak point in the tree's stem and leaves the tree more vulnerable to stem breakage during windstorms. Also, there is a general decline in the remaining root system. The compression makes it more difficult for the roots to move water and minerals up to the foliage, and more difficult for the tree to move photosynthates ("food") to the roots. Over time, the root system declines in health and the aboveground canopy and foliage likewise declines. How deep is too deep? Based on the previous studies, as little as one inch of soil over the root collar flare can disguise stem-girdling roots until it is too late. With sugar maple in particular, the significant decline in health began when the soil depth was 4 inches. Regardless, there is no biological reason to bury root collar flares. Healthy trees growing in native forests have visible root collar flares at the soil line. Therefore, it is not logical to believe that planting deeper is better. To prevent early decline or sudden failure during windstorms, make sure that those first, main order roots that originate at or near the soil line are planted at that depth in the landscape. Make certain that those roots are at the top of the soil ball of balled-in-burlap trees and containerized trees before you dig the planting hole. Either dig down through the top of the soil ball with a trowel until you find those first roots, or probe down with a stiff wire to find the depth of soil over the roots. If there are 4 inches of soil over the roots of the purchased plants, dig the hole 4 inches shallow and scrape off the excess soil before mulching the newly planted tree or shrub. These few minutes of care at planting time will help ensure that you enjoy a healthy, longlived landscape tree or shrub.
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It Might Be Worth Saving Transplanting Trees and Shrubs Part I: Preparing for the Move "I don't know anything about planting trees, but my neighbor told me that you shouldn't plant in the autumn in Minnesota." "I was at the local nursery last weekend and they had signs advertising "Fall is for Planting"." Who should you believe?
Part of this contradiction involves mythical information vs. factual information. A bigger part of the contradiction relates to the differences between planting and transplanting. Most of the mythical information revolving around the blanket statement "you shouldn't plant in the autumn in Minnesota" is a misunderstanding. Planting is literally placing a plant in the ground at its (hopefully) permanent growing site. Transplanting involves digging a plant from one site and transferring the tree or shrub to a new site. When planting is done, theoretically, no roots are lost. When transplanting is done the majority of the tree or shrub's original root system is cut off during the process. It's SHOCKING! The loss of roots during the transplanting procedure normally induces a health condition called transplant shock. This condition is actually less ominous than the term implies, and the vast majority of transplanted trees and shrubs fully recover in a relatively short amount of time. During this shock period, however, the abbreviated root system must recover and reestablish a more characteristic "root:shoot" balance. During this recovery period the tree or shrub exhibits retarded growth above ground (contrary to what's going on below ground), maybe a little branch or twig dieback and often less and smaller leaf production. As the tree or shrub is growing through this recovery period, it's more vulnerable to stressful weather and landscape conditions that healthy plants would normally be able to tolerate. Short-term drought, hot and windy weather, and early, deep freezes can result in some abnormal damage to the plants. Whether the plant is a native one or an introduced one, they're all vulnerable to transplant shock. When the leaves are falling, the roots are growing. Autumn, especially early through mid-autumn, is actually an excellent time to transplant many trees and shrubs in Minnesota because of the aggressive root growth going on below ground. Normally, the autumn soil temperatures and moisture content in most Minnesota landscapes are ideal for root growth. That's why most field nurseries "root-prune" trees and shrubs in the weeks during late summer to early autumn. Warm soil temperatures + uniform soil moisture = new roots. Spring is also an excellent time period for transplanting, especially if it can be done after the ground thaws and the leaves emerge. Both
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Minnesota Tree Care Advisors spring and autumn seasons present the advantage of moving largely dormant plants, and the disadvantage of not knowing what the following months will be like (weather-wise). Droughty, hot and windy summers can be just as stressful on newly transplanted trees and shrubs as early, windy, bitterly cold and long winters. Why take the chance and potentially waste all the efforts of transplanting something when it's easier to just buy a new tree or shrub? Good question! Maybe the plant has some sentimental value, such as a memorial tree or a shrub that you propagated from your grandparent's garden?…GOOD REASON! Maybe the tree has some historical significance, and is worth preserving, such as the "Eagan Oak" that was transplanted in 2001?…GOOD REASON! Maybe it's a unique species, or a species that isn't normally found growing in Minnesota, such as the Japanese maple in Grand Marais, or a topiary juniper that has taken you years to develop?… GOOD REASON! Maybe it's just a beautiful specimen, the most perfect potentilla you've ever seen?…GOOD REASON! Maybe the tree or shrub is in pretty bad shape, unhealthy, unshapely, and a new site could improve its appearance?…BAD REASON! As a rule of thumb, if the plant is in poor health or poor condition, it probably would be best to transplant it to the chipper and then to the mulch pile. You can do this during any season. Okay, you've convinced me. Can I move anything, spring or fall? Well, yes, you can move anything, but it may not survive! Literally, just about any tree or shrub can be moved, but there are definite limits to success (a.k.a., the plant actually lives). Smaller trees and shrubs transplant more successfully. They're younger and recover from the transplant shock much sooner and easier. Plus, there's a better chance that you will be able to transplant a larger percentage of the roots if the plant is smaller. For instance:
Root and Top Growth of a One-Inch Caliper Tree Following Transplanting (Reyes, 2002) A 1" caliper tree would have a root diameter of 4.5 feet. By nursery standards a root ball of about 1.5 feet would be moved. Less than 5% of the root system is transplanted. First Year The tree is under severe water stress soon after transplanting. With good care the stress diminishes, and the root system diameter should increase to 4.5 feet (100% of the original) by the end of the first year. Roots and top are now balanced and the tree should grow normally.
Root and Top Growth of a Four-Inch Caliper Tree Following Transplanting
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Minnesota Tree Care Advisors A 4" caliper tree would have a root diameter of 18 feet. A root ball of 3.5 feet would be moved. Less than 5% of the root system is transplanted in the root ball. First Year Root system diameter increases to 6 feet, 9% of original volume. With less than 10% of the absorbing roots to support a full crown (top), the tree is often under severe water stress, inhibiting top growth, including bud formation.
Second Year Root system increases to 9 feet, 23% of original volume. The tree is frequently under water stress, inhibiting current season growth.
Third Year Root system diameter increases to 12 feet, 41% of original volume. As root/top balance is gradually restored, the tree is exposed to less water stress and growth improves.
Fourth Year Root system diameter increases to 15 feet, 60% of original volume. The effective rate of root generation accelerates as the overall diameter of the root system increases.
Fifth Year Root system diameter increases to 18 feet, 100% of original volume. Roots and crown and the tree should grow normally.
Healthy plants transplant more successfully. It takes a lot of the plants stored energy to establish a new, more characteristic root
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Minnesota Tree Care Advisors system. If a plant is unhealthy, it probably has a very poor, energy reserve system. Not only will it be more difficult for this plant to recover its root system from the shock of transplanting; the energy drain could push this tree or shrub over the edge from unhealthy to dead. How do you know if it's healthy? If the foliage is undersized for the species, it may not be healthy. If the canopy (branches with leaves) is sparse for the species, it probably isn't very healthy. If there is a lot of branch dieback, it's probably not healthy. If there is decay in the stem/s, infestations of boring insects and/or infectious diseases of the stem or leaves‌transplant it to the chipper. SOME plant species just do better if moved in the spring: Carpinus
Acer rubrum
Berberis
Magnolia
Betula
Cotoneaster
Populus
Cornus
Ilex
Quercus (most species)
Prunus
Pinus
Chamaecyparis
Pyrus
Rhododendron
Crataegus
Salix
Taxus
Tilia tomentosa
Tsuga Viburnum
Stick with Spring Spring best, Autumn w/care Early Autumn
How can I improve the chances of a successful transplant? Build up the health of the plant before the move. If you're planning on moving the plant in the spring, start with the health program the preceding autumn or summer. If it's nutrientstressed, fertilize it. Don't allow it to become water-stressed‌ keep the soil uniformly moist. Control any insect pests or diseases. Prune out any dead wood and/or weakly attached branches. Mulch as much of the root zone as you can stand. This gets rid of grass competition, lessens the need for constant watering, and keeps the soil warmer into late autumn (for best root growth). Root prune the plant, at least one season (spring or autumn) before the move. Root pruning woody plants encourages a more compact and dense root system. Therefore, when you finally move it, the tree or shrub will have a higher percentage of its most important roots contained within a smaller soil volume. As a rule of thumb, for each inch of stem caliper, root prune at a distance of 10-12 inches out from the stem of the plant. For instance, if the tree has a one-inch stem caliper, the diameter of the rootpruned area would be 20-24 inches. Simply determine the appropriate distance from the stem, draw a circle around the stem with this distance as the radius, and sink the blade of your digging spade down as deep as you can go all the way around this circle. This one practice
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Minnesota Tree Care Advisors will dramatically reduce the transplant shock on the plant when it is finally transplanted the following season or year.
You've sold me on the idea of transplanting, but the tree is just too big for me to move it. Are there companies that specialize in transplanting large trees and shrubs? Yup. There are several companies in Minnesota that specialize in transplanting large plants with various sizes of tree spades. However, these companies are busy, and it would be smart to include contacting them at least one season before the transplant date. A Partial Listing of Companies That Transplant Large Trees and Shrubs: Minnesota Valley Landscape
952-445-4004
Halla Nursery
952-445-6555
Bob Matiski Tree Moving
651-436-1709
Witzel Tree Moving
651-459-4581, 651-769-1759
Strese's Tree Service
507-645-6137; cell 612-282-3526
References cited: Reyes, Jonah. 2002. Arboriculture Myth Exposed: Bigger is Better? Tree Care Advisor
Even small trees suffer from wind damage. This small hackberry with a broken leader and branches is not worth the time and effort it takes to move a tree.
The hackberry pictured here is worth moving. A good dominant leader and a decent branching habit makes it a likely candidate.
Pruned root stubs with a summers re-growth
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Malus spp. “Spring Snow” root stock
Fraxinus pennsylvanica “Green Ash” root stock
Root Pruning encourages a more compact and dense root system. Therefore, when you finally move it, the tree or shrub will have a higher percentage of its most important roots contained within a smaller soil volume.
Step 1: Measure the trunk diameter
Step 2: For every inch of Trunk diameter - measure out from the stem 10-12 inches and use that distance as the radius to trace a circle around the tree
Step 3: Using a 12-18 inch spade Follow the outline and fully insert the spade, completely encircling the tree.
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Root pruning complete.
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It Might Be Worth Saving Transplanting Trees and Shrubs Part II: Making the Move Weeks or months have now passed since you made the decision to move the tree or shrub and hopefully prepared that plant for the journey. I'm sure that to some people, all of this planning seems a bit excessive. If all you are doing is moving a 24 inch Potentilla, I'd have to agree with you. Just dig it up and move it anyway you can‌it WILL live. However, since of lot of other readers may be thinking about moving a 12 foot spruce, or 20 year old lilacs or a 5 inch caliper basswood, the excessive planning is much more necessary.
Figure 1: Green Ash - Pot-in-Pot container study. Root Pruned prior to growing season
A lot has been happening below ground since you root-pruned that tree or shrub a few weeks or months ago, but unless you have x-ray vision it hasn't been obvious. Every root that you cut during that process has rewarded you ten-fold‌at least. The two photographs in Figure 1 show the effect of timely root pruning. The image to the left is of a green ash, immediately after root pruning. The image below is the same tree, four months later. The net result is not only a much more extensive root system, but one that is contained in a much smaller area. This visually exhibits why root-pruned plants survive transplanting so much better than those not pruned. Before you transplant, take a look up, around and beneath. It's impossible to avoid talking about tree or shrub placement in a transplanting primer. After all, the plant is theoretically being moved to a "better" site than before. Add these next steps to your checklist:
1. Look up. Don't plant in a site where the mature tree or shrub can interfere with utility lines or views from windows. And don't fool yourself by thinking that regular pruning can keep the plant size in check. Too much work, too hard on the plant, too easy to forget. After four months in a container.
2. Look around. Will the new placement create a blocked sight line? For instance, as it matures, will it block the view of the street from your driveway as you back out? Or the clear view at an intersection of streets? If so, don't plant it there. If the proposed planting site is within 60 of the street, the street is a busy street and you know from past experience that a lot of deicing salt is used, don't plant the tree or shrub there unless it's known to be tolerant of Minnesota's main source of pollution. For a list of trees and their tolerances to deicing salt exposure, refer to "Minimizing De- Icing Salt Injury to Trees," (Johnson, Sucoff, 1995). If the plant could get so broad that it would interfere with pedestrians walking by or lawn maintenance, don't plant it there thinking that pruning would contain the problem. 3. Look down. Actually, have Gopher State One Call look down and deep for you. I should have mentioned this in part I before
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Minnesota Tree Care Advisors you rootpruned, and hopefully none of you severed any utilities. Definitely contact them now at: 651-454-8388, or 800252-1166, or www.gopherstateonecall.org. It seems like a bit of an annoyance, but it's cheap insurance. While you're looking down, check the soil for compaction or drainage problems. If you can dig two spades lengths deep into the soil, you don't have a compaction problem. If you need to jump up and down on the shovel and have your 300 pound neighbor do it, too‌you have a compaction problem. Compaction problems can be alleviated somewhat by an extensive site preparation (e.g., loosening the soil in an area 10 feet in diameter), and it's so much easier to do that before you move the new tree or shrub. Poor drainage is another story, though. To check for drainage, dig or auger a hole 24 inches deep. Fill with water and allow it to completely drain. Fill a second time. That second filling should be drained within 24 hours. If it isn't, drainage may be an issue. If the transplanted tree is a sugar maple‌it's an issue. If it's a silver maple, it probably isn't. Correcting soil drainage problems is difficult and often expensive. Your best move is to avoid them if they could become problematic for tree or shrub health. Might as well have that soil tested, too. The most critical thing to determine is the soil pH (whether it's acidic or alkaline), and don't think that just because the native soils are acidic that your soil will be acidic. Most "urbanized" soils are alkaline, some just slightly and others obscenely. If the soil pH is 7.5 or so, and the transplanted tree is a river birch‌don't plant it there! It WILL decline and die prematurely. And as with poor drainage, soil alkalinity is difficult and expensive to change.
I'm ready to transplant the tree but it's autumn now. Should I wait until spring? In Part I, I hinted that time of year may be more of a perceived problem, rather than a real problem. Certainly, there are some plants that are best and most successfully moved in the spring (see Part I for a partial listing), but quite honestly, there's little documented research that success or failure rates differ dramatically by seasons (obvious exceptions would be mid-winter and mid-summer). Most of you reading this live in the southeastern part of Minnesota. That's just a demographic fact, not a location prejudice. Upstate New York is very similar climate-wise to much of Minnesota, especially the southeastern part of Minnesota. In a documented, two-year research experiment conducted by Cornell University in upstate New York (Buckstrup and Bassuk, 2000), hackberry (Celtis occidentalis), ironwood (Ostrya virginiana) and bicolor oak (Quercus bicolor) survived and grew just as well when transplanted in the autumn as they did in the spring. Sometimes better in the autumn. That's research-based information. It's not inclusive for every tree or shrub imaginable, but it is factual and more reliable than memory or "my neighbor said" information.
What ARE the most important factors for transplant success?
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Transplant as many roots as possible. Never let them dry out. Prepare the new site for root growth. Plant the tree or shrub at the right depth. Take care of the plant after the move, for the life of the plant (figuratively and literally). Transplant as many roots as possible If you root-pruned the tree or shrub at least one season before the move, the plant now has a much more concentrated root system in a more confined area. This means that you will be able to move a much more extensive root system. The way it is moved depends on species and size. Bare-root transplanting is just as the term implies: moving the plant's root system with little to no soil attached. Whenever possible, this is the preferred method because it is relatively simple, the (lighter) plant is easier to handle and move, any root problems become obvious and easier to correct, and in fact, you can usually move a larger root system this way. It is not usually recommended for moving conifers or trees larger than 2 inches in caliper (but those rules can be bent).
1. If possible, dig down a few inches beyond that rootpruning trench that you dug a season ago. You will hit some new roots, but the majority of the roots will be contained within the diameter of the root-pruned area. As you are digging down, pry the shovel to lift the roots and loosen the soil. 2. Loosen the soil within the diameter of the new trench. If the soil is very dry, it sometimes helps to moisten it a few inches deep the day before you dig. My implement of choice for loosening the soil is a "potato fork," which is similar to a short pitchfork with broad and flat tines. Loosening the soil is walking a fine line between freeing the roots and cutting them. You don't want to cut all the roots off, just loosen the soil from them so the plant can be lifted.
Digging Bare-root
3. If there are any roots growing down, slip under the root mass with your shovel or use a loppers to cut those roots. Now the plant should be free from the growing site and you can shake most of the remaining soil off. 4. Keep the roots moist. Immediately after freeing the plant from the soil, "heel" it back in with loose soil and moisten it. An alternative would be to cover the roots with wet straw or woodchips and cover with a tarp or plastic. Those roots can die in minutes when exposed to air.
Bare-root stock
Now, I've left a couple "holes" that need filling. Caliper. This is the thickness of the stem, which is measured approximately 6 inches above the ground line. However, if the stem measurement taken at that point is greater than 4 inches
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Minnesota Tree Care Advisors thick, move up the stem another 6 inches and record the stem thickness at that point. Diameter of root mass. The American Association of Nurserymen has developed the "American Standard for Nursery Stock." (reference and address in concluding reference section). According to the standards, a tree with a 1 inch caliper should have a 18 inch diameter bare root system‌AS A MINIMUM. A 2 inch caliper tree should have a 28 inch diameter bare root system‌ AS A MINIMUM. For a 3 inch caliper tree, at least 38 inches. For a 3 foot tall shrub, 14 inches in diameter; 16 inches for a 4 foot shrub; 18 inches for a 5 foot shrub; and 20 inches for a 6 foot shrub. Keep in mind that these are MINIMUM dimensions. The more roots you transplant with the tree or shrub, the more successful the move will be.
Balling and burlapping (B&B) the root system requires much more skill, patience and muscles! For those larger trees and/or conifers that traditionally move better with a soil ball surrounding the roots, this and moving the plants with a tree spade (mechanical digger) are the preferred methods. The irony of it is that the root system is actually smaller (according to the Standards) for B&B dug versus bare-root dug plants. For instance: 2 inch caliper B&B should have a minimum soil ball diameter of 24 inches (compared to 28 for bare-rooted). Ball and Burlap
If you decide to ball and burlap the plant, the process is a bit different. 1.
Again, if the soil is dry, moisten it to a depth of several inches the day before the move. Carefully scrape away all excess surface soil until you find the first branch root/s. This should be the very top of your soil ball when the plant is finally dug.
2.
Use a flat spade, similar to a "sod-cutting" spade, instead of a rounded or "spoon" shovel. Turn the face of the shovel away from the stem of the plant as you dig down around the minimum root ball diameter.
3.
As you sink the spade into the soil and cut the roots, press the handle back toward the stem and scoop the soil out away from the soil ball. This is the opposite action taken when bare-rooting a plant. This action compacts the soil into a solid root/soil ball with
Foliage and branches tied up
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each spade of soil scooped away.
Compacting and removing soil.
4.
After the first "lap" around the root ball diameter, begin a second lap digging down deeper. In effect, you will be digging this trench around the soil ball two spade-lengths deep.
5.
Begin "shaving off" soil from the soil ball. Don't try to move a soil ball if there are no roots to hold it intact, because it won't stay intact! Shave off soil until you hit enough roots that you can be confident that it will hold together. Then, begin cutting down and into the bottom center of the soil ball. This is known as "tapering" the soil ball, and again, if you don't hit any roots, don't try to move that soil with the soil ball. Keep tapering in until you begin cutting roots.
6.
Once the soil ball is shaved and tapered, fold up a sheet of burlap or an old sheet, slip it down into the hole against one side of the soil ball and roll the soil ball back onto the burlap or sheet. Pull half of the burlap or sheet under the soil ball and up around the opposite side.
7.
Pull up the four corners of the burlap or sheet, tie them to each other and snug up the wrapping. Sometimes it is necessary to "bind up" the burlap or sheet with twine or a rope to hold it all together.
8.
Get some help and lift the plant out of the hole.
Shave and taper the ball.
Burlapping
Tied up and ready to move
That sounds like a lot of work and very confusing! You're right! It took me about four months to learn how to ball and burlap professionally when I started working for a nursery as a college
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Minnesota Tree Care Advisors student. It's very hard work, frustrating at times, and every tree and shrub is a bit different. I'd recommend that you hire someone experienced at this art if it needs to be done, or have it moved with a tree spade. The move As mentioned earlier, if the soil is compacted, loosen it as much as you can tolerate. Then pass the shovel or roto tiller off to someone else and have them loosen it as much as they can tolerate. This will pay off in the form of a shorter transplant shock period and a healthier, longer-lived tree or shrub. Replanting the shocked tree or shrub is at least as important as the digging process. For detailed information on the best planting practices, refer to "Planting Trees and Shrubs for Long-Term Health," which is listed in the concluding reference section. The steps are simple, however. 1.
Measure the depth of the root system if it's barerooted, or the soil ball depth if it's B&B or tree spade dug.
2.
That measured depth is the deepest that the new planting hole should be. If you are to err, err on the side of planting high. This doesn't mean that the roots will be sticking up out of the ground. You will just need to haul in more good soil to cover those higher roots, creating a planting berm.
3.
The width of the hole depends on the nature of the soil, the compacted nature to be specific. If the new planting site has beautiful, loose soil, the width of the planting hole is not a big issue. It should be large enough to place the soil ball/roots into it and work the backfill soil in around those roots. If the soil is very compacted, then the wider the planting hole, the better.
4.
Double-check that planting depth and make sure those first branch roots are no deeper than the landscape surface. Don't worry, they're not going to die; they will end up with a light dressing of mulch over them.
Measure the soil ball
determine depth
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Double check depth of 1st branch roots
5.
If the tree or shrub has been balled and burlapped, backfill about half way up the soil ball depth and then cut off the remaining burlap or sheet above that point.
6.
Complete the backfilling, water the soil ball/root area thoroughly and mulch the planting site with 2-4 inches of the mulch of your choice. Don't pile ANY mulch up against the stem, however.
7.
Religiously water, sometimes every day depending on the season, soil drainage and size of the transplant. Allow the soil to drain after each irrigation, but never allow the roots and the soil around the roots to completely dry out
8.
Don't prune off branches to compensate for root loss! This practice may seem logical, but it's not bio-logical. If branches subsequently die, then prune them off.
There is a "magic bullet!" Everyone wants to know what they can do to ensure transplant success. Is it fertilizer? No. Is it soil fungi or bacteria? No. Is it cow manure, peat moss, composted leaves? No. It's water. Not too much, not too little, not once a week, not one inch of water per week, not just before planting, not only after planting. It's the amount needed to keep the roots moist from the time you begin digging until the tree or shrub is safely beyond transplant shock (at least one year). And then after that, for the life of the tree. When water is maintained at an optimum level, then fertilizers, soil amendments, microbial inoculations may be beneficial. If water is lacking or excessive, those other amendments are either worthless or damaging to plant health. Occasionally, trees may need some support via stakes for a short period of time after transplanting. For more information on staking and guying trees, refer to the Forest Resources Extension web site listed in the reference section. Often, trees and shrubs need some winter protection from hungry critters. Again, refer to the Forest Resources Extension web site.
References American Association of Nurserymen. American Standard for Nursery Stock, ANSI Z60.1. 1250 I Street, N.W., Suite 500, Washington, D.C. 20005. Buckstrup, Michelle J. and Nina L. Bassuk. 2000. Transplanting Success of Balledand- Burlapped Versus Bare-Root Trees in the Urban Landscape. Journal of Arboriculture, 26(6): November, 2000. P. 298308.
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Minnesota Tree Care Advisors Hargrave, Rebecca, Gary Johnson and Michael Zins. 2002. Planting Trees and Shrubs for Long-Term Health. University of Minnesota Extension Service, MI- 07681. 13 pages. Johnson, G.R. and Ed Sucoff. 1995. Minimizing De-Icing Salt Injury to Trees. University of Minnesota Extension Service, FO-1413, 7 pages. Forest Resources Extension, University of Minnesota. Click on Tree Health. (view forest website) Minimizing De-Icing Salt Injury to Trees (view minimizing website) Rodent Damage. Click on Trees - Rodent Damage (view forest website) Urban and Community Forestry. Click on Urban and Community Forestry (view forest/urban website) Planting. Click on Planting (view forest/planting website) Staking and Guying. Click on Staking and Guying (view forest/staking website)
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Pruning Trees and Shrubs
Mike Zins and Deborah Brown, Extension Horticulturalists FO-00628 Revised 1997 Pruning is a horticultural practice that alters the form and growth of a plant. Based on aesthetics and science, pruning can also be considered preventive maintenance. Many problems may be prevented by pruning correctly during formative years for a tree or shrub. REASONS FOR PRUNING 1.
Prune to promote plant health Remove dead or dying branches injured by disease, severe insect infestation, animals, storms, or other adverse mechanical damage. Remove branches and branch stubs that rub together. Avoid topping trees. Removing large branches leaves stubs that can cause several health problems. It also destroys the plant’s natural shape and promotes suckering and development of weak branch structure.
2.
Prune to maintain plants; intended purposes in a landscape, such as: encouraging flower and fruit development, maintaining a dense hedge, or maintaining a desired tree form or special garden forms.
3.
Prune to improve plant appearance Appearance in the landscape is essential to a plant’s usefulness. For most landscapes, a plant’s natural form is best. Avoid shearing shrubs into tight geometrical forms that can adversely affect flowering. Alter a plant’s natural form only if it needs to be confined or trained for a specific purpose. When plants are pruned well, it is difficult to see that they have been pruned! Prune to: control plant size, keep evergreens well-proportioned, or remove unwanted branches, waterspouts, suckers, and undesirable fruiting structures that detract from plant appearance.
4.
Prune to protect people and property. Remove dead branches. Have hazardous trees taken down o Prune out weak or narrow-angled tree branches that overhang homes, parking areas, and sidewalks — anyplace falling limbs could injure people or damage property. Eliminate branches Eliminate branches that interfere with street lights, traffic signals, and overhead wires. REMEMBER, DO NOT attempt to prune near electrical and utility wires.
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Minnesota Tree Care Advisors Contact utility companies or city maintenance workers to handle it. Prune branches that obscure vision at intersections. For security purposes, prune shrubs or tree branches that obscure the entry to your home. PRUNING BEGINS AT PLANTING TIME receive. It is critical for young trees to be trained to encourage them to develop a strong structure. (See Figure 1) Too many young trees are pruned improperly or not pruned at all for several years. By then it may become a major operation to remove bigger branches, and trees may become deformed. At planting, remove only diseased, dead, or broken branches. Begin training a plant during the dormant season following planting. Prune to shape young trees, but don’t cut back the leader. Remove crossing branches and branches that grow back towards the center of the tree. Figure 1. Prune this young tree to remove
As young trees grow, remove lower branches gradually to raise the crown, and remove branches that are too closely spaced on the trunk. Remove multiple leaders on evergreens and other trees where a single leader is desirable Pruning young shrubs is not as critical as pruning young trees, but take care to use the same principles to encourage good branch structure. When planting bare root deciduous shrubs, thin out branches for good spacing and prune out any broken, diseased, or crossing/circling roots. When planting bare root deciduous shrubs for hedges, prune each plant to within 6 inches of the ground. Newly planted shrubs require little pruning if they were containergrown or were dug with a soil ball.
PRUNING LARGE ESTABLISHED TREES Leave the pruning of large trees to qualified tree care professionals who have the proper equipment. Consider the natural form of large trees whenever possible. Most hardwood trees have rounded crowns that lack a strong leader, and such trees may have many lateral branches. The three most common types of tree pruning are:
1. Crown Thinning-selectively removing branches on young trees throughout the crown. This promotes better form and health by increasing light penetration and air movement. Strong emphasis is on removing weak branches. (Don’t overdo it on mature trees.) 2. Crown Raising — removing lower branches on developing or mature trees to allow more clearance above lawns, sidewalks, streets, etc.
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3. Crown Reduction — removing larger branches at the top of the tree to reduce its height. When done properly, crown reduction pruning is different from topping because branches are removed immediately above lateral branches, leaving no stubs. Crown reduction is the least desirable pruning practice. It should be done only when absolutely necessary.
PROPER BRANCH PRUNING To shorten a branch or twig, cut it back to a side branch or make the cut about 1/4 inch above the bud. Always prune above a bud facing the outside of a plant to force the new branch to grow in that direction.
Pruning small branches
Pruning large braches To remove large branches, three or four cuts will be necessary to avoid tearing the bark. Make the first cut on the underside of the branch about 18 inches from the trunk. Undercut one-third to onehalf way through the branch. Make the second cut an inch further out on the branch; cut until the branch breaks free. Before making the final cut severing a branch from the main stem, identify the branch collar. The branch collar grows from the stem tissue around the base of the branch. Make pruning cuts so that only branch tissue (wood on the branch side of the collar) is removed. Be careful to prune just beyond the branch collar, but DON’T leave a stub. If the branch collar is left intact after pruning, the wound will seal more effectively and stem tissue probably will not decay. The third cut may be made by cutting down through the branch, severing it. If, during removal, there is a possibility of tearing the bark on the branch underside, make an undercut first and then saw through the branch. Research has shown wound dressing is not normally needed on pruning cuts. However, if wounds need to be covered to prevent insect transmission of certain diseases such as oak wilt, use latex rather than oil-based paint.
TIMING The late dormant season is best for most pruning. Pruning in late winter, just before spring growth starts, leaves fresh wounds exposed for only a short length of time before new growth begins the wound sealing process. Another advantage of dormant pruning is that it’s easier to make pruning decisions without leaves obscuring plant branch structure. Pruning at the proper time can avoid certain disease and physiological problems: Pruning at the proper time can avoid certain disease and physiological problems:
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To avoid oak wilt disease DO NOT prune oaks during April, May, or June. If oaks are wounded or must be pruned during these months, apply wound dressing to mask the odor of freshly cut wood so the beetles that spread oak wilt will not be attracted to the trees. To avoid increased likelihood of stem cankers, prune honeylocusts when they are still dormant in late winter. If they must be pruned in summer, avoid rainy or humid weather conditions. Prune apple trees, including flowering crabapples, mountainash, hawthorns and shrub cotoneasters in late winter (FebruaryearlyApril). Spring or summer pruning increases chances for infection and spread of the bacterial disease fireblight. Autumn or early winter pruning is more likely to result in drying and die-back at pruning sites. o Some trees have free-flowing sap that “bleeds” after late winter or early spring pruning. Though this bleeding causes little harm, it may still be a source of concern. To prevent bleeding, you could prune the following trees after their leaves are fully expanded in late spring or early summer. Never remove more than 1/4 of the live foliage. Examples include: all maples, including boxelder butternut and walnut birch and its relatives, ironwood and blue beech. Trees and shrubs that bloom early in the growing season on last year’s growth should be pruned immediately after they finish blooming: Apricot
clove currant
Juneberry
Azalea
flowering plum
lilac
Chokeberry
cherry
magnolia
Chokecherry
forsythia
early blooming spirea
Shrubs grown primarily for their foliage rather than showy flowers should be pruned in spring, before growth begins: alpine currant
dogwood
purpleleaf sandcherry
Barberry
honeysuckle
smokebush
Buffaloberry
ninebark
sumac
burning bush
peashrub
Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.
PRUNING HEDGES After the initial pruning at planting, hedges need to be pruned often. Once the hedge reaches the desired height, prune new growth back whenever it grows another 6 to 8 inches. Prune to within 2 inches of the last pruning. Hedges may be pruned twice a year, in spring and
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Minnesota Tree Care Advisors again in mid-summer, to keep them dense and attractive. Prune hedges so they’re wider at the base than at the top, to allow all parts to receive sunlight and prevent legginess.
RENEWAL PRUNING FOR OLDER OR OVERGROWN SHRUBS Every year remove up to one-third of the oldest, thickest stems or trunks, taking them right down to the ground. This will encourage the growth of new stems from the roots. Once there are no longer any thick, overgrown trunks left, switch to standard pruning as needed.
PRUNING EVERGREENS With few exceptions, evergreens (conifers) require little pruning. Different types of evergreens should be pruned according to their varied growth habits. Spruces, firs and douglas-firsdon’t grow continuously, but can be pruned any time because they have lateral (side) buds that will sprout if the terminal (tip) buds are removed. It’s probably best to prune them in late winter, before growth begins. Some spring pruning, however, is not harmful. Pines only put on a single flush of tip growth each spring and then stop growing. Prune before these “candles” of new needles become mature. Pines do not have lateral buds, so removing terminal buds will take away new growing points for that branch. Eventually, this will leave dead stubs. Pines seldom need pruning, but if you want to promote more dense growth, remove up to twothirds of the length of newly expanded candles. Don’t prune further back than the current year’s growth. Arborvitae, junipers, yews, and hemlocks grow continuously throughout the growing season. They can be pruned any time through the middle of summer. Even though these plants will tolerate heavy shearing, their natural form is usually most desirable, so prune only to correct growth defects.
USE THE RIGHT TOOLS FOR PRUNING The right tools make pruning easier and help you do a good job. Keeping tools well-maintained and sharp will improve their performance. There are many tools for pruning, but the following will probably suffice for most applications: A good pair of pruning shears is probably one of the most important tools. Cuts up to 3/4 inches in diameter may be made with them. Lopping shears are similar to pruning shears, but their long handles provide greater leverage needed to cut branches up to 11/2 inches in diameter. Hedge shears are meant only for pruning hedges, nothing else. They usually cut succulent or small stems best. Pruning shears
Hand saws are very important for cutting branches over 1 inch in diameter. Many types of hand saws are available. Special tri-cut or razor tooth pruning saws cut through larger branches — up to 4 inches in diameter — with ease.
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Minnesota Tree Care Advisors Pole saws allow for extended reach with a long handle, but they must be used carefully as it’s difficult to achieve clean cuts with them. Lopping shears
Small chain saws are available for use on larger branches. Operators must wear protective clothing and exercise caution when using them. Never use chain saws to reach above your shoulders, or when you are on a ladder. Mike Zins and Deborah Brown are Extension Horticulturists with the University of Minnesota Extension Service.
Hedge shears
This publication is based on an earlier version written by Mervin Eisel, former Extension Horticulturist. Produced by Communication and Educational Technology Services, University of Minnesota Extension Service.
Hand saws
Copyright Š 2002 Regents of the University of Minnesota. All rights reserved.
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