TNLA would like to thank the following companies for being Membership Sponsors
GOLD MEMBERSHIP SPONSORS
Barky Beaver Mulch & Soil Mix, Inc.
BASF
Blankenship Farms and Nursery
Bobcat of McMinnville Botanico, Inc.
BWI of Memphis
Cam Too Camellia Nursery, Inc.
Cherry Springs Nursery
Delta Mulch and Materials, LLC
Flower City Nurseries
Gravely NYP Corp.
Putnals Premium Pine Straw, Inc.
Randall Walker Farms
Riverbend Nurseries, LLC
Super-Sod
Swafford Nursery, Inc.
Swift Straw Tennessee 811
Tennessee Valley Nursery, Inc.
Warren County Nursery, Inc.
Youngblood Farms, LLC
SILVER MEMBERSHIP SPONSORS
3F - Flanders Family Farm
Bert Driver Nursery
Dayton Bag & Burlap Co.
Mid-South Nursery
Mike Brown’s Wholesale Nursery, LLC
Old Courthouse Nursery
Rusty Mangrum Nursery
Samara Farms
Turf Mountain Sod
“All the trees are losing their leaves, and not one of them is worried.”
–
DONALD MILLER –
Dear Members,
As we are looking forward to the changing of seasons and the work ahead of us, we can always remember that the plants aren’t worried about shedding their leaves. We work all year for the opportunity to give our customers great-looking plants and service. This year has come with challenges such as storms and weather that can make for difficult growing conditions. We can look to the same plants we grow to gain perspective on our attitudes toward the future. We know that soon they will shed their leaves and get ready for the changing season; and before you know it, they emerge again. We are a strong sector of the green industry and know that when leaves begin to fall the prospect for another great season is just beginning.
We are blessed in this industry to have such a great opportunity to work with each other and service our customers to the best of our ability. A great time to capitalize on this is at our trade show which is generating a lot of buzz. TNGRO will be at the Farm Bureau Expo Center in Lebanon, TN on September 28th and 29th. There will be several exhibitors set up giving attendees great networking opportunities in all fields of our industry. Another chance to network and have fun is our upcoming golf tournament on October 13th at the McMinnville Country Club. Our association greatly appreciates the sponsors that help make these events possible. We also want to thank our association’s secretaries that do the daily work to make these events happen.
Thank you,
Terri Turner
TNLA President
You are invited to attend the TNLA reception, business meeting, and awards ceremony, Thursday, September 28, 2023, 5:00 pm at the Farm Bureau Expo Center in Lebanon, TN.
Gardening Practices of Native Plant Purchasers
By Dr. Alicia Rihn1, Dr. Bridget Behe 2 , Dr. Susan Barton 3, and Dr. Ariana Torres 4
1University of Tennessee, Assistant Professor, Agricultural & Resource Economics Department
2Michigan State University (retired)
3University of Delaware, Professor, Department of Plant and Soil Sciences
4Purdue University, Associate Professor, Department of Horticulture and Landscape Architecture and Department of Agricultural Economics
There is a lot of buzz about native plants. Many factors contribute to this increased attention including heightened demand by customers. But what is the motivation behind this enhanced interest? How do customers view native plants? Are there differences in customer behavior that can be associated with these perceptions? Understanding how customers view products is important because perceptions influence behavior. If alignments occur between communications with the customer (e.g., promotions, informational signage, etc.) and customer perceptions of the item/service, then sales are more likely to occur. The first step in better understanding the drivers of consumer behavior is to assess the current practices of consumers to establish a foundation of understanding. This article summarizes a 2023 online survey of 2,066 U.S. homeowners that assessed the relationship between the customer’s perceived importance of incorporating native plants into residential landscapes and what they describe as their current gardening practices.
We identified distinct customer segments based on their perceived importance of native plants. Fifty percent of the sample reported that incorporating native plants into their landscapes/gardens was very or extremely important, to them. About 33% indicated that incorporating native plants was moderately important, and 17% indicate that this objective was only slightly or not important to them (Figure 1). On average participants were 57 years old; 77% were female, 46% had obtained a bachelor’s degree or higher, 42% lived in rural areas, 45% lived in suburban areas, and 13% lived in urban areas. The sample of surveyed respondents was selected to provide equal representation across the 5 U.S. regions (20% per region – Northeast, Midwest, Southwest, Northwest, and South) to account for regional differences related to native plants.
Figure 1. Perceived Importance of Native Plants in Residential Landscapes and Gardens (n=2,066)
Very / Extremely Important 50% No / Slight Importance 17% Moderately Important 33%
Participants self-reported their use of different environmentally focused gardening practices. They rated the listed practices on a 7-point scale, where “1” corresponded to not at all like me, and “7” equaled exactly like me (Figure 2). Among respondents, their top-rated gardening practice was recycling gardening packaging (rating 5.6), followed by using pollinator friendly plants (rating 5.5), using low fertilizer and pesticide varieties (rated 5.4), using native plants (rating 5.2), using soil amendments (rating 5.1), and using low irrigation varieties (rating 5.0). Intermediate ratings were captured for growing some of one’s own food (rating 4.7), using organic gardening practices (rating 4.2), purchasing organic plants (rating 4.1), and composting on property (rating 3.8).
Participants self-reported their limited participation in collecting rainwater (rating 3.1).
When results were evaluated as a function of participants’ self-reported perceptions of importance to them about native plants, clear differences are observed (Figure 3). Participants who perceived that incorporating native plants was “very-to-extremely” important rated all of the gardening practices as more characteristic for themselves than other groups that reported either “moderate” importance or “slight-to-no” importance in native plant use. Within the “veryto-extremely” important native plant users, their highest rated gardening practices were using pollinator friendly plants or native plants (rating 6.0), recycling gardening packaging (rating 5.9), using varieties that require less fertilizer or pesticides (rating 5.8), using varieties that require less irrigation (rating 5.4), and using soil amendments (rating 5.4). The segment that viewed incorporating native plants as moderately important rated the gardening practices at an intermediate level. Within this group, their top-rated gardening practices included recycling gardening packaging (rating 5.4), using pollinator friendly plants (rating 5.3), using plant varieties that require less fertilizer or pesticides (rating 5.2), and using soil amendments (rating 5.0). Lastly, the segment who rated native plants as low or not important in their landscape plant usage rated recycling gardening packaging the highest (rating 4.8), followed by using plant varieties requiring less fertilizer or pesticides (rating 4.6), using pollinator friendly plants (rating 4.5), using soil amendments (rating 4.3), and using plant varieties that use less water (rating 4.2).
Table 1 shows the relationship between the gardening practices and native plant user segments. Among the native plants as very/extremely important segment, probability increased for using native plants (by 11.2%), pollinator friendly plants (by 5.1%), plant varieties requiring less water (by 2.6%), organic gardening practices (by 2.2%), composting (by 1.3%), recycling packaging (by 1.3%), and rainwater barrels or collectors (by 1.1%).
I use pollinator friendly plants (e.g., plants that attract bees, hummingbirds, or butterflies).
I use plant varieties that require less fertilizer or pesticides.
I use native plant species in my garden.
I use soil amendments to improve soil health.
I use plant varieties that require less water.
I grow some of my own food.
I use organic gardening practices (e.g., using organic plants and organic fertilizers and/or soil amendments).
I purchase plants that are organically grown.
I compost on my property and use the compost in my garden (e.g., garden waste, leaves, cuttings, or other…
I use a rainwater barrel or collector.
Gardening Practice Use (higher value = more like me)
3. Self-Reported Participation in Different Gardening Practices, by Importance of Native Plants (n=2,066). Note: Significant differences were observed between importance groups for each gardening activity at the 5% level.
I use pollinator friendly plants (e.g., plants that attract bees, hummingbirds, or butterflies).
I use plant varieties that require less fertilizer or pesticides.
I use plant varieties that require less water.
I use soil amendments to improve soil health.
I grow some of my own food.
I use organic gardening practices (e.g., using organic plants and organic fertilizers and/or soil amendments).
I purchase plants that are organically grown.
I compost on my property and use the compost in my garden (e.g., garden waste, leaves, cuttings, or other…
I use a rainwater barrel or collector.
Figure
Figure 2. Self-Reported Participation in Different Gardening Practices (n=2,066)
Table 1. How Different Gardening Practices Influence Probability of Segment Membership (n=2,066). Note: Only significant predictors (at 5%) of segment membership are presented below.
Gardening Practice
I use organic gardening practices.
I compost on my property and use the compost in my garden.
I recycle gardening packaging.
Midwest participants were 9.0% less likely to be represented within this group. For the native plant use as moderately important segment, being in the Midwest increase their probability of being in this group by 4.6%. Conversely, all of the other practices decreased their probability of being in this segment by varying degrees. Similar trends to the moderately important segment were observed for the no/slight importance segment.
Results from this study and knowledge gained about consumers helps define gardening practices used by individuals who view native plants as an important part of their landscape design and plantings. Perceived importance of native plants is partially driven by participation in eco-friendly gardening practices. This behavior may stem from internal drivers and motivations that are related to increased awareness of environmental issues. There is an opportunity to implement promotional messaging that aligns these two topics and encourage customers to select plants that align with their desires and landscaping needs. For example, adding native plant signage and positioning garden center native plant displays near eco-friendly gardening merchandise and plants may be a way to encourage crossselling behavior among native plant purchasers. Of note, across the customer segments, pollinator friendly plants were deemed important, meaning that the use of point-of-sale information to inform customers about plants that benefit pollinators is one way to encourage purchasing behavior. Lastly, signage is also imperative to aid customers in identifying native plants and their benefits in the retail environment.
Acknowledgements: This research was supported by a grant from the Horticultural Research Institute (HRI). Its contents are solely the responsibility of the authors and do not necessarily represent the views of HRI.
Full citation: Rihn, A.L., B.K. Behe, S. Barton, and A. Torres. 2023. Greater appeal of native plants for environmentally conscious consumers. Journal of Environmental Horticulture, 41(1): 7-13. https:// doi.org/10.24266/2573-5586-41.1.7
Landscape Recovery following the December Flash Freeze in Tennessee
By Lee Rumble, Commercial Horticulture Extension Agent, UT/TSU Extension—Knox County
The Flash Freeze Event
At midnight on December 22, 2022, air temperatures in the Knoxville area were 46ºF. Across the next six hours, temperatures plummeted to 10ºF and as the day continued, air temperatures continued to decline to 3ºF by midnight on December 23, 2022. In a 24-hour period, Knoxville experienced a 43-degree temperature drop…and similar conditions were observed across the state. The rapid and dramatic decline in temperature was compounded by strong winds and sustained freezing temperatures (< 32ºF) that persisted across the state for three more days! It was not until noon on December 27, 2022, that temperatures would once again rise above 32ºF (Time and Date AS, 2023).
Understanding Dormancy in Higher Plants
Trees and shrubs have dealt with freezing temperatures for millions of years. Fortunately, researchers and growers have spent contemporary time focusing on how plants protect themselves from freezing conditions. At the dawn of the 19th century, Sir Thomas Knight pioneered early studies on dormancy in plants. In 1801, he conducted experiments that demonstrated the need of woody perennial plants to endure a period of dormancy before plants could resume growth in the spring (Fadón et. al., 2019). This research, and the work of many other scientists and scholars throughout the 20th century, helped to form the basis of our current understanding about dormancy in higher plants. Today, we recognize that four major conceptual stages in dormancy occur in deciduous plants (Fadón et. al., 2019):
• Dormancy Induction – The first step in winter cold-hardiness of plants begins with annual leaf drop that follows in response to decreasing photoperiod and temperatures. Conditions stimulating dormancy induction vary greatly among species (and cultivar).
• Endo-dormancy – Achieving the conditions that represent inherent dormancy requirements within the plant. After endo-dormancy needs are met, release from endo-dormancy will be most influenced by low nighttime temperatures that occur after an acclimation period that we now describe as “chilling hours”.
• Eco-dormancy – A quiescent, or resting, state. Once a plant has become acclimated to cold temperatures, eco-dormancy is then controlled and maintained by environmental factors external to the plant. A period of sustained and mildly elevated temperatures could trigger resumption of plant growth. Often, however, growth is prevented by other unsuitable environmental conditions.
• Growth Resumption – When plant-favorable environmental conditions again resume, phenological changes next begin that lead to renewed growth, including foliar bud break and initiation of floral blooming.
At their core, these four stages seem relatively straightforward. However, the number of interactions that occur within plants leading to emergence from dormancy are actually quite numerous and complex. Thresholds of photoperiod, temperature, and cold acclimation are met, then overcome, while transport blockage, phytohormones, genetic and epigenetic regulation, and carbohydrate reallocation all work tirelessly together in the background at each stage.
In east Tennessee, most of our mature deciduous trees showed no immediately noticeable damage. Individuals of many tree species were already fully acclimated to the freezing December temperatures. The same was not true, however, for many of our evergreen tree and shrub species. Throughout the winter months, evergreen species do not go fully dormant and continue to absorb light energy (photons). Under favorable environmental conditions, evergreen species are still able to photosynthesize; thus, utilizing their “evergreen” leaves for longer periods of time. Yet, under unfavorable conditions (i.e., freezing temperatures), the light rays that are absorbed by chloroplasts in leaves and needles cannot be used by the plant, resulting in plant damage. Freezing temperatures inhibit CO2 assimilation, leading to the overexcitation of photosynthetic machinery, and create light stress in evergreen foliage. This condition has been called chlorophyll bleaching or “solarization” (Öquist and Huner, 2003). The interactions between light, freezing temperatures, and also desiccation can be damaging (if not lethal) to evergreen leaves. In our area, broadleaf evergreens and needled evergreens really took a hit from the flash freeze event, and it was these plants that we received the most calls about.
What Happened to Plants
Most often, freeze damage can be associated with ice formation within plant cells. This ice formation within the cell is what ultimately punctures the cell walls leading to a loss of function (Bumgarner et. al., 2023). Certainly, with the rapid and sustained temperature drops, cell damage was likely to occur in some plants. With such a rapid drop in temperature, plants were unable to implement internal defense measures to tolerate the sudden freezing temperatures. This, in addition to excessive wind gusts (averaging 19 mph here in Knoxville) helped to further desiccate (dry out) many of our plants. Within two weeks, noticeable signs of damage appeared across the state and the calls came swarming in. Cool-season turfgrasses, ground covers, conifers, borderline hardy shrubs, and both broadleaf and needled evergreen plants were most noticeably affected. Turfgrasses showed brown necrotic tissues, conifers almost immediately began to bronze, borderline hardy shrubs began to defoliate, and broadleaf evergreens started showing signs of solarization (Figure 1). This flash freeze event appeared to be most destructive to those “borderline hardy” species listed as USDA Plant Hardiness Zone 7 or Zone 8 plants. Aucuba, Camellia, Cryptomeria, Distylium, Ficus, Indian Hawthorn (Rhaphiolepis spp.), Loropetalum, and other genera all showed initial signs of damage. Yet it was not just borderline hardy plants that were affected; we also saw damage on Azalea, Arborvitae, Boxwoods, Chamaecyparis spp., Cherry Laurel (Prunus laurocerasus), Hollies (Ilex spp.), Magnolia, Nandina, Crape Myrtle, Lenten Rose (Helleborus spp.), and even English Ivy.
Interestingly, we observed that site location and exposure to microclimates within the landscape mattered. In some landscapes, species were seemingly killed to the ground, while the exact same species in another landscape may well have escaped the freeze damage. For those of us in the green industry, this serves as a clear reminder of the importance not only of careful plant species (and cultivar) selection, but also attention to where and how we place our plants within the landscape. We also observed that plants that had been pruned late into fall 2022, and that had developed new growth since pruning that had not hardened off, were more drastically affected (Figure 2). In many cases, plants that were already unhealthy and lacked vigor eventually succumbed to this freeze event—this was most noticeable in Cherry Laurels (Prunus laurocerasus) that went into the event already stressed (Figure 3).
in late fall,
newly stimulated growth that had not hardened off which was most affected by the flash freeze and sustained cold weather. Compare the difference between the unpruned (and unaffected) boxwood directly behind the row of pruned shrubs. (Photo taken January 4, 2023 by Lee Rumble)
Figure 1: Loropetalum (Loropetalum spp.) showing initial chlorophyll bleaching (or solarization) damage from December freeze event. (Photo taken January 4, 2023 by Lee Rumble)
Figure 2: Boxwoods (Buxus spp.) had been pruned
2022. It was the
Figure 3: A Common Cherry Laurel (Prunus spp.) shrub killed to the ground. (Photo taken January 4, 2023 by Lee Rumble)
What We Told People to Do
Almost immediately calls began from across the state—from Memphis to Johnson City. We encouraged people to be patient and stay calm. But with April and May still several months away, this advice was a tough sell given the drastic effects seen on many of our landscape plants. Most of the calls were initiated with “Should I cut my plants back now”? Due to this influx of calls, our University of Tennessee Extension Horticulture Workgroup collaborated to prepare and
distribute a Fact Sheet: Handling the Holiday Freeze in Your Lawn & Landscape (Bumgarner et al. 2023) to help our clientele understand that follow up recommendations about these types of events are often a “wait and see” game. Only time can tell us which plants are able to weather a freeze event.
As plants continued to defoliate in the days that followed and calls continued well into January, we encouraged people to implement a “scratch test” on their favorite winter-damaged plants. By scratching bark from a small section of stems
and twigs within the canopy, we could better see if the tissues beneath the bark were green (a viable plant) or brown (a dead plant). More experienced gardeners likely also understood twig pliability and a plant’s ability to rebound after slight pressure is applied to the uppermost twigs. Still, with many of our favorite plants defoliating rapidly, and spring temperatures rising, people were anxious to get out and try to fix the problem. We encouraged people to limit their pruning until the full extent of what was to come was made apparent with the arrival of spring bud break. A second added benefit of waiting to prune is that by leaving aboveground damaged tissues, especially for low-growing perennial plants, the stems and entwined leaf litter proved useful in providing a little more insulation to the crown and roots of these plants.
What Has Progressed Since
Since the initial damage we saw within days or weeks to many of our broadleaf evergreen plants, a more extensive portion of the foliage on these plant species ultimately succumbed to the damage that occurred. Initial solarization, loss of plant vigor, and subsequent defoliation were seen in most of the species listed previously in this article. While many plant species might have defoliated entirely, the ultimate survival and viability of many individual plants was still promising. Frequently, our scratch tests showed green (viable) tissues just beneath the bark. For a few species (particularly Indian Hawthorn, [some] Hollies, and Cryptomeria) we quickly saw brown scratch test results (dead stem tissues); it was these plants we became more worried about.
What We’re Seeing Now
By the end of May, we saw most plants rebound, while other specimens and species have succumbed to their injuries. It is important to remember that rarely does one single factor kill an established, mature woody ornamental shrub or tree. Instead, they die as the result of a cumulative series of stressful events that build up with time. Eventually, the combined losses of vigor, limbs, and foliage will lead to premature plant death.
Another negative effect that has since emerged following this freeze event is the appearance and expansion of vertical frost cracks in the bark and wood of some of our deciduous landscape trees (Figure 4a). Frost cracks most commonly occur on the south and/or west side of trees, on plant species that have particularly thin bark, and for tree trunks that may be exposed to direct sunlight. Warming daytime temperatures and cool nighttime temperatures in early spring combine to promote the expansion and contraction between the bark and inner wood—ultimately leading to frost cracks that appear as vertical splits on the main stems and scaffold limbs of trees and shrubs.
Unfortunately, with frost cracks, the damage usually gets worse before it gets better (Figure 4b). For smaller frost cracks, these should be left alone, allowing the tree’s natural wound response to attempt to compartmentalize (i.e., close) these injuries across time—do not use wound sealants (e.g., paint, tar, or expanding foam) on exposed wood tissues. If frost cracks are large and severe, you might be better off consulting with an ISA Certified Arborist to see if bark tracing, or carefully cutting away the peeling bark back to sound tissue using a sterilized surgical blade, may be a good option for your tree (Bark Splitting on Trees, 2018). Carefully removing (by surgical means) larger pieces of loose bark allows the tree a better opportunity to compartmentalize larger wounds. However, once the internal wood is exposed to the external environment, the elements, wood-decay Fungi, and various insect pests will all be able to access and further expedite decay within the exposed wood. Ultimately, the severity and extent of these frost cracks will determine the survival fate of these affected species.
While there is no clear cut answer to fix the damage caused by freezing temperatures, it is important to realize that, even for those specimens and species that appear to have survived this freeze event, they will still be susceptible and under stress well into 2023. Understanding this stress and managing it throughout this year will be a good way to help promote landscape plant vigor and a quicker, stronger chance of recovery.
How to Best Handle Future Freeze Events
While we get little say in future freeze events, taking a few precautions at the time of plant selection can go a long way in ensuring that the plants in our landscapes are hardy enough to handle another freeze event such as the one experienced in December 2022. Start by implementing a few best management steps that can go a long way in helping landscape plant selections to not only survive, but thrive:
• Select cold hardy species (and cultivars) adequate for our USDA Plant Hardiness Zone 7.
• Avoid late summer fertilization and/or pruning, which might stimulate new growth late in the season.
• Water trees and shrubs, especially evergreens, during dry periods until the ground freezes.
• Use just a few inches of mulch to conserve soil moisture and insulate the roots from freezing temperatures. Older, decomposed mulch should be removed before adding new mulch to an established landscape tree or shrub bed.
• Take appropriate steps to manage pests and encourage plant vigor throughout the year.
• Identify and understand how to best utilize (or avoid) microclimates that occur within every landscape.
Resources Cited and Additional Reading:
Bumgarner, Natalie, Jim Brosnan, Amy Fulcher, Lucas Holman, Lee Rumble, Taylor Reeder, Celeste Scott, and Justin Stefanski. 2023. Handling the Holiday Freeze in Your Lawn & Landscape. University of Tennessee Extension Fact Sheet. https://westtn.tennessee.edu/wpcontent/uploads/sites/35/2023/01/Handling-the-Holiday-Freeze-inYour-Lawn-Landscape.pdf
Fadón, Erica, Eduardo Fernandez, Helen Behn, and Eike Luedeling. 2020. A Conceptual Framework for Winter Dormancy in Deciduous Trees. Agronomy 10, 241.
Öquist, Gunnar, and Norman Huner. 2003. Photosynthesis of Overwintering Evergreen Plants. Annual Reviews Plant Biology 54, 329-55.
Plant Disease Diagnostic Clinic, Cornell. 2018. Bark Splitting on Trees: Various. Cornell University Fact Sheet. http://plantclinic.cornell. edu/factsheets/barksplitting.pdf
Time and Date AS December 2022 Weather Graph – Knoxville, 2023. Time and Date AS 1995-2023. Web. 10 May 2023. https://www.timeanddate.com/weather/usa/knoxville/ historic?month=12&year=2022
Figure 4a: A vertical frost crack on the main trunk of a Red Oak (Quercus spp.) tree. (Photo taken March 28, 2023 by Lee Rumble)
Figure 4b: A comparison of the original frost crack (Figure 4a) on the main trunk of a Red Oak (Quercus spp.) tree nearly 8-weeks following the initial injury. Due to the excessive bark loss, little hope of survival is predicted for this tree. (Photo taken May 10, 2023 by Lee Rumble)
Weed Management Strategies in Nursery Crop Propagation
Dr. Anthony Witcher 1 and Isha Poudel 2
1 Associate Professor; Tennessee State University, Otis L. Floyd Nursery Research Center
2 TSU Masters graduate student alumna; Currently a PhD Student in University of Tennessee Plant Sciences Department, West Tennessee Research and Education Center
Plant propagation is a key component of the nursery industry. Some nurseries only propagate for their own use while other nurseries specialize in propagating liners for sale and growing on to a finished salable size. Many nursery crops are propagated by seed including many tree species and rootstock used for grafting. Other crops, including herbaceous perennials and woody shrubs, are produced from vegetative cuttings. Weeds are a major issue during propagation (Fig. 1), yet limited weed control options are available during propagation. As weeds become established, they compete with rooted cuttings for light and resources, and many weed species can produce seed within a few weeks, quickly infesting larger areas in liner production beds. Although actively growing weeds can be removed from containers and flats prior to shipping, the remaining weed seeds will germinate and be a problem during later stages of crop production. Manual weed removal (hand weeding) is the most common method of weed control in propagation, but these efforts are time consuming and costly, and the work requires extra labor demands from staff members who have, in recent years, become less available for hire. As a result, development of improved weed control methods is needed to reduce labor and cost inputs during propagation and to improve finished crop quality.
Sanitation Practices
Weeds that infest propagative material can be spread by seed coming from contaminated container substrates, used containers, floors within the propagation area and surrounding areas, stock plants, and by workers. To prevent weed seed infestation, container substrates, especially pine bark in bulk piles, should be stored in a protected area or indoors. Propagation containers that are re-used should be thoroughly cleaned with high pressure water sprays to remove weed seeds, especially seeds with a sticky outer coating such as bittercress (Cardamine spp.) and woodsorrel (Oxalis spp.). Surrounding production areas including nearby container production blocks, floors of the propagation spaces (Fig. 2), and stock plants used for cuttings should be maintained weed free to prevent spread of seeds from weeds in established crops and nonproduction areas, roadways, and nursery borders.
Post-emergent herbicides can be used to control actively growing weeds, but care must be taken to avoid contact with foliage of desirable crops. Several post-emergent herbicides are labeled for use in enclosed structures (such as greenhouses) and can be used to control weeds during propagation. These products include diquat (Reward®), glufosinate (Finale®), glyphosate (Roundup®), and pelargonic acid (Scythe®). Preemergent herbicides are used to prevent weed seed establishment in container-grown crops in production, on gravel production pads, and in non-crop areas such as gravel drives and walkways. Pre-emergent herbicides such as flumioxazin (Sureguard®) and indaziflam (Marengo®) can be used on greenhouse and shade house floors, but these products must be applied prior to moving in flats and containers with plants.
Herbicide Use in Propagation
Propagation by seed and cuttings involves the initiation, growth, and development of new roots that will be sensitive to certain herbicides. As a result, pre-emergent herbicides have not been widely used during propagation. Pre-emergent herbicides function by inhibiting germination or root/shoot development. Sensitivity to active ingredients in pre-emergent herbicides can vary by chemical class and among plant species. Pre-emergent herbicides in the dinitroaniline family act as root inhibitors (by inhibiting mitosis in root cells) and numerous research reports noted reduced rooting percentage and root development when used in cutting propagation. Root inhibiting herbicides such as oryzalin (Surflan®), pendimethalin (Pendulum®), prodiamine (Barricade®), and trifluralin (Treflan®) should not be used in cutting propagation.
Figure 1. Container-grown oak seedlings that have become infested with bittercress weeds (photo by A. Witcher).
Figure 2. An infestation of bittercress seedlings in the gravel floor within a propagation area (photo by A. Witcher).
Several other pre-emergent herbicides are considered non-rootinhibiting resulting from their different modes of action. For example, oxadiazon (Ronstar®) and oxyfluorfen (Goal®) are Group 14 herbicides that disrupt cell membrane synthesis while isoxaben (Gallery®) is a Group 21 herbicide that inhibits cell wall synthesis. Previous research reported oxadiazon was safe to apply prior to sticking cuttings of several crop species including Abelia spp., Buxus spp., Euonymus spp., Ilex spp., and Rhododendron spp. (Johnson and Meade, 1986; Thetford and Gilliam, 1991). In another study, oxyfluorfen was reportedly safe when applied prior to germination of several large-seeded tree species including Carya spp, Juglans spp., and Quercus spp. (South and Carey, 2005). In other studies, isoxaben could be safely applied over-the-top of small seedlings of several crop species and during cutting propagation of Loropetalum spp. (Cochran et al., 2008; Halcomb and Fare, 1997). Nevertheless, limited information is available for using pre-emergent herbicides in propagation.
Research At Tennessee State University
Most work that previously has evaluated pre-emergent herbicide uses in propagation was completed over twenty years ago. There are newer products and formulations that may be viable for weed control in propagation systems. Other types of products such as mulches may be alternatives for weed control in sensitive crops (like many herbaceous perennials, dogwood, and hydrangea) and inside greenhouses. In recent years, several studies have been completed at the Tennessee State University Otis L. Floyd Nursery Research Center in McMinnville, TN evaluating pre-emergent herbicides and mulches in seedling and cutting propagation.
In the first study, container-grown tree seedlings were exposed to treatments of several different pre-emergent herbicides or mulch materials (Table 1). Containers planted with acorns of sawtooth oak (Quercus acutissima) and willow oak (Q. phellos) were treated prior to seed germination. Seedlings of four other tree species including kousa dogwood (Cornus kousa), sweet gum (Liquidambar styraciflua), sweetbay magnolia (Magnolia virginiana), and yellow poplar (Liriodendron tulipifera), were transplanted to containers and then treated after three days. No physical damage was observed for any of the tree species, yet reduced growth was observed for kousa dogwood seedlings exposed to dimethenamid-P+pendimethalin, pendimethalin, prodiamine, trifluralin, and pine pellets and yellow poplar seedlings exposed to trifluralin (Fig. 3). Weed control efficacy varied by product and weed species but pine pellets provided excellent control of bittercress and large crabgrass.
In a second study, three pre-emergent herbicides (isoxaben, isoxaben+dithiopyr, and oxadiazon+oxyfluorfen) were applied at three different timings (two weeks before sticking, at sticking, and two weeks after sticking cuttings). Cuttings of butterfly bush (Buddleja davidii ‘Nanho Blue’), holly (Ilex cornuta ‘Dwarf Burford’), and crape myrtle (Lagerstroemia indica ‘Catawba’) were tested. Compared to the non-treated control, herbicide type and application timing had no negative effects on root development for crape myrtle or holly; however, the herbicides containing isoxaben reduced rooting for butterfly bush. Neither of those products were labeled for use in butterfly bush. Oxadiazon+oxyfluorfen (Regal O-O®) also provided excellent control of four common weed species: bittercress (Cardamine hirsuta), crabgrass (Digitaria sanguinalis), creeping woodsorrel (Oxalis corniculata), and mulberryweed (Fatoua villosa)]. Applying pre-emergent herbicides to substrates prior to sticking cuttings would provide more uniform coverage to the container substrate surface and reduce labor costs.
inch depth)
Herbicide (High Label Rate)
Treflan F trifluralin
Treflan 5G trifluralin
Pendulum AC pendimethalin
Pendulum 2G pendimethalin
Gallery SC isoxaben
Snapshot 2.5TG trifluralin + isoxaben
Barricade 4FL prodiamine
Freehand G dimethenamid-P + pendimethalin
Figure 3. Tree seedlings three months after being treated with pre-emergent herbicides and mulches. Six plant species included (from top to bottom) sawtooth oak, willow oak, sweet gum, sweetbay magnolia, yellow poplar, and kousa dogwood (photo by A. Witcher).
Table 1. Mulches and pre-emergent herbicides evaluated in a seedling propagation trial.
Spirea Tor
Miss Kim Lilac
In a third study, mulch type and depth were evaluated for rooting cuttings of three crop species: butterfly bush, crape myrtle, and hydrangea (Hydrangea paniculata ’Phantom’). Mulches included coarse vermiculite, paper pellets, pine pellets, and rice hulls applied at 0.5- or 1-inch depth prior to sticking cuttings (Fig. 4). No differences in rooting percentage were observed for any treatments. Crape myrtle root dry weight was lower for paper pellets (both depths), but no differences were observed for butterfly bush or hydrangea. Both depths of pine pellets and paper pellets provided effective weed control of bittercress, crabgrass, creeping woodsorrel, and mulberry weed seeds (Fig. 5). By contrast, rice hulls provided poor weed control, which is surprising due to their effectiveness when used in container production. The frequent mist required for cutting propagation likely negated the hydrophobic properties of the rice hulls. Economically, pine pellets are comparable in cost to rice hulls based on coverage area. Paper and pine pellet mulches can be alternatives to pre-emergent herbicides and used with sensitive crop species and within enclosed structures.
Currently, there are no pre-emergent herbicides labeled for use in propagation. Many products have restrictions that limit use in small diameter containers (less than four inches) and on seedlings and/or non-rooted cuttings. Additionally, there are no pre-emergent herbicides labeled for use within enclosed structures because they may become volatile once activated by irrigation. Nevertheless, some products lack restrictive language thus may be allowed for use in outdoor (shade house) propagation at the grower’s own risk. Mulches and some pre-emergent herbicides may have potential for use in seedling and cutting propagation, however further research is needed to screen pre-emergent herbicide safety to additional crop species. Growers should always read herbicide labels to identify any use restrictions (that may include site, sensitive crop species, container sizes, etc.). Growers should also conduct small trials with individual products and crop species prior to large scale adoption.
Additional Reading References:
Cochran, D.R., Gilliam, C.H., Eakes, D.J., Wehtje, G.R., and Knight, P.R. (2008). Herbicide use in propagation of Loropetalum chinense ‘Ruby’. J. Environ. Hortic. 26:139-143.
Halcomb, M.A., and Fare, D.C. (1997). Tolerance of seedlings to preemergence herbicides. Proc. South. Nurs. Res. Conf. 42:315-318.
Johnson, J. R., and Meade, J.A. (1986). Pre-emergent herbicide effect on the rooting of cuttings. Proc. Intl. Plant Prop. Soc. 36:567-570.
South, D.B., and Carey, W.A. (2005). Weed control in bareroot hardwood nurseries. USDA Forest Serv. Proc. 35:34-38.
Thetford, M., and Gilliam, C.H. (1991). Herbicide use in propagation: Effects on rooting and root growth of stem cuttings. J. Environ. Hort. 9:21-23.
For more information on weed control practices in nursery crop propagation and production, contact Dr. Anthony Witcher (awitcher@tnstate.edu).
Figure 5. Bittercress germination in propagation containers topdressed with mulch (0.5 inch depth). From top to bottom: No mulch, rice hulls, pine pellets, and paper pellets (photo by I. Poudel).
Figure 4. Paper pellet, pine pellet, and rice hull mulches (left to right) when applied dry (top) then saturated with irrigation (bottom) (photo by I. Poudel).
Horticulture at Work in the UT Gardens
An update on the latest news and programs in Horticultural Therapy at UT
By Dr. Derrick Stowell, CTRS, HTR Education and Horticultural Therapy Program Administrator, UT Gardens, Department of Plant Sciences
The
University of Tennessee (UT) Gardens offers horticultural therapy programming to a wide variety of individuals and organizations throughout Tennessee. These programs have been designed to connect the mission of the University of Tennessee Institute of Agriculture (UTIA) through education, research, and outreach. Since 2012, the UT Gardens horticultural therapy program has served over 9,000 individuals with a variety of medical conditions, as well as service, outreach, and programming to 2,610 health care professionals from around Tennessee. As importantly, across more than 10 years the horticultural therapy program has also served 41 interns who have benefitted from horticultural therapy-focused internship opportunities. These interns, along with graduate students, staff, and faculty advisors to the horticultural therapy program have conducted and published research on horticultural therapy. Most recently, a successful horticultural therapy certificate program has been launched. This article focuses on two elements that connect our horticultural therapy program to the broad mission of the University of Tennessee Institute of Agriculture (UTIA); 1.) the creation of the University of Tennessee’s first undergraduate certificate program and, 2.) a collaboration with the Tennessee AgrAbility Project.
The Horticultural Therapy Certificate program
The University of Tennessee Horticultural Therapy Certificate program was launched in 2022 with its first cohort. This certificate program consists of nine hours of college credit in horticultural therapy, PLSC 411 – Introduction to Horticultural Therapy (three hours), PLSC 412 – Horticultural Therapy Programming and Techniques (three hours), and PLSC 413 – Horticultural Therapy Program Management
These courses have been accredited by the American Horticultural Therapy Association. This program was developed as an online certificate program to increase accessibility to students from around the country to high quality horticultural therapy education and training. The program is an accelerated program and can be completed in 21 weeks. The final week of PLSC 413 is an in-person session held at the UTIA campus in Knoxville, Tennessee. The third cohort will launch in fall 2023 and be completed by Spring of 2024. Students in this certificate program come from a variety of professional backgrounds including, but not limited to recreational therapy, occupational therapy, and counseling. Other students who attend the program are interested in starting a new career using horticultural therapy as a treatment modality. There has been increasing interest in plants and using horticulture to help improve health and well-being and the Horticultural Therapy Certificate prepares students to develop their own horticultural therapy programming. The assignments undertaken during the program focus on the horticultural therapy basics and then build upon those basic components. Students who complete the program have an opportunity and the capability to develop their own horticultural therapy program plans that can be used at their place of work, or that can assist them to obtain new employment using horticulture as therapy.
The Tennessee AgrAbility Project: A Collaborative Horticultural Therapy Workshop for Veterans
Another active endeavor at the UT Garden includes horticultural therapy workshops for veterans. The UT Gardens has been collaborating with Tennessee AgrAbility Project since 2017. This collaboration created and implemented horticultural therapy workshops for
Supplies provided for an activity at the May 2023 horticultural therapy workshop.
veterans. The first workshops were developed to educate veterans on the therapeutic benefits of horticulture and to connect project participants to resources that the Tennessee AgrAbility Project offers. Veteran participants can benefit from farm assessments and the Tennessee New Farmer Academy. Outcomes from first round of workshops, which were supported by a National Institutes of Food and Agriculture grant, included positive connections made with other veterans, learning about career opportunities for veterans, and learning about the positive health benefits of cultivating plants (Stowell & Burnett, 2019). The second round of workshops included virtual workshops and training as well as in-person programming. In this second round, the UT Gardens and Tennessee AgrAbility Project partnered with a third organization, called FrontLine Gardens, to connect with veterans. FrontLine Gardens is a non-profit organization that provides raised bed gardens to veterans and connects them to the therapeutic benefits of horticulture. The mission of FrontLine Gardens is “to assist in the journey to healing veterans, first responders, and gold star families with PTSD physically, emotionally, and spiritually through therapeutic gardening.” The work of AgrAbility and UT Gardens has helped ensure that FrontLine gardens has received valuable tools to help with their organization’s overall success. Stephanie Trost, executive director of FrontLine Gardens, shared that:
“[At] the University of Tennessee, Derrick Stowell has been with us every step of the way. They helped us understand the complexity and the benefits of Horticultural Therapy. As we launched, they have stayed by our side offering our new gardener’s classes to help them succeed. We would not be where we are today, if it was not for UT and their support.”
HEEDING
THE CALL… and Then Paying It Forward
“The Horticultural Therapy Certificate Program at UT-Knoxville introduced me to something that has become my new passion. As a disabled veteran and flower farmer, I saw this opportunity as another means for me to give back to my fellow veterans. Using plants as a method of healing and moving forward is something I wanted to be a part of and share with others.
Since becoming one of the first graduates of the program, I’ve been able to help design and manage a therapeutic horticulture program for the soldiers assigned to the Ft. Campbell, KY Soldier Recovery Unit and I also provide therapeutic horticulture activities for the Clarksville, TN Steven A. Cohen Military Family Treatment Clinic. I also was just elected as a Director-at-Large for the American Horticultural Therapy Association.”
CHARLEY JORDAN
Military Veteran & Inaugural Class of 2022 Horticultural Therapy Program Certificate Earner
Attendees from UT Gardens, Tennessee AgrAbilty Project, and FrontLine Gardens participated in the FrontLine ‘23 horticultural therapy workshop in May.
Inaugural members of the 2022 Horticultural Therapy Certificate Program visiting gardens designed by Dr. Alan Solomon at The University of Tennessee GATOP Arboretum and Education Center.
Charley Jordan shares well-earned Pride of Place and Achievement with a view of his flower production fields at Jordan Farms in Indian Mound, TN.
The final piece of the AgrAbility collaboration is a training program designed for Master Gardeners. To accomplish this, the UT Gardens provided training on the therapeutic benefits of horticulture to Master Gardens and then connected Master Gardeners to veterans who have had a garden built by FrontLine Gardens. The project also included workshops for veterans that not only connected veterans to the therapeutic benefits of gardens, but it also connected them to additional resources that FrontLine Gardens can offer. Since the beginning of horticultural therapy programming for this project, seven workshops have been held across Tennessee including in Knoxville, Nashville, Clarksville, Memphis, and one online workshop.
If you work with veterans and are interested in having UT Gardens come and present a horticultural therapy workshop at your facility, please contact us at 865-974-7151 or dstowell@utk.edu
For more information about the horticultural therapy certificate program, visit https://plantsciences.tennessee.edu/horticulturaltherapycertificate/.
The Tennessee AgrAbility Project is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Award Number 2021-41590-34809.
References / Further Resources
FrontLine Gardens – https://frontlinegardens.org/
Deeds, E., J. Rennie, and D. Stowell. (2023). Therapeutic Benefits of Gardening and Accessible Garden Design. University of Tennessee Extension Publication W-1153. Retrieved from https://extension.tennessee.edu/publications/Documents/W1153.pdf
Stowell, D. and A. Burnett. (2019). Promoting the Profession of Horticultural Therapy through Partnerships. Journal of Therapeutic Horticulture. 29(1), 39-46.
UT Gardens Horticultural Therapy Program – https://utgardens.tennessee.edu/locations/knoxville/horticultural-therapy-outreach/
University of Tennessee Horticultural Therapy Certificate Program –https://plantsciences.tennessee.edu/horticulturaltherapycertificate/
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Editors
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CELEBRATING 20 YEARS!
CONTAINER LINERSLANDSCAPE READY
Good foundations matter. That's why we utilize air pruning pots to give our container materials the best root system early in their lives. Our container liners are used by premium growers in both field and container production as well as conservation, restoration, mitigation, and remediation efforts.
We take pride in our work. With our consistent grading & attention to detail in nutrition and pest management growing practices, we aim to deliver a sustainably grown, vigorous product. We just grow great plants.
