Winter Wellness for Landscape Ornamentals

Feature Story Winter Wellness for Landscape Ornamentals

Abrutal snowy winter- a mild cold winter – is one better for tinue to push new growth. Cut back on watering practices plants then the other? Not necessarily. Damage to plants in the late summer and early fall. This holding back of water due to cold temperatures can occur during several times of and nutrients supports early development of hardiness for the year: spring and fall; the coldest part of winter; and when the winter ahead. cold temperatures occur after a warm period of weather. An However, before the ground freezes in the late fall/early early snow that stays around or gets replenished through the winter, give trees and shrubs a good watering, enough to winter months serves a good insulator against cold damage. reach an 8-10 inch depth once a week. When the ground Cold temperatures cause injury to trees, is frozen, it may not absorb rain washrubs and ornamentals in the land- ter or snow readily. The moisture in the scape. The xylem, conducting vessels soil can be absorbed by the roots below of plants, in small branches of trees and the ground. During a dry winter, hollies shrubs can be damaged by cold temper- and evergreens or plants located under a atures, but the injury is not noticed until roof eaves may need to be watered once a the spring when the growth is slowed, month if there is a warm spell. Be careful there are less flower buds or the branch around walk ways and parking lots, as you is completely dead. This type of injury do not want to create an icy situation. usually occurs in mid-winter. These cold Sunny winter days can cause injury winter temperatures may also kill dor- to trees. Bark temperatures can be 10oF mant flower buds and cause dieback in warmer then air temperatures as the overwintering evergreen plants. A cold sun shines on the tree. A rapid drop in winter with little or no snow may be temperature may cause and injury called considered mild, but drying winds will sun scald. Frost cracks can occur when take moisture out of plants. there is repeated injury from temperature

Spring frosts can damage the tender fluctuations due to sun exposure. Newly shoots, flowers and fruits of plants that planted trees and thin barked trees such may have started coming out of dormancy too soon due to warmer than Wrap young trees with reflective white tree guards Credit: University of Minnesota as Cherry, Crabapple and Maple are susceptible to these injuries. Over time, frost average winter temperatures. Temper- cracks go deeper into the trunk of the tree atures several degrees above average minimum temperatures and a callus forms along the injury. The wood inside might in the late fall before plants have reached their maximum decay, leading to structural problems. Evergreen trees are less dormancy or hardiness can cause injury to plants, including susceptible to frost cracks then deciduous trees. Lone trees deciduous trees and shrubs that have already lost their leaves. in the landscape are an easy target for frost cracks. Planting

Plants naturally prepare themselves for the winter by go- lower growing trees or shrubs around the tree can provide ing into dormancy. Plants do need those cooler tempera- some protection. tures and shorter days of the fall and a reduction in watering Fortunately trees can be protected from sunscald and frost and nutrients to prepare themselves for the winter. To aid cracks. Using a polyurethane spiral wrap or wrapping Kraft the plants in their preparation for winter, avoid fertilizing paper around the trunk can help keep the trunk temperatures ornamental plants after mid-July/early August. Fertilizing constant. The wraps can also provide protection from wildstimulates new growth, which will not be hardy enough for life damage during the winter months. The wraps should be winter. The plant may not go into dormancy – it will con- applied in the fall, but removed in the late spring. Apply the

by Madeline Flahive DiNardo, County Agent / Associate Professor, Rutgers Cooperative Extension of Union County

wrap starting at the bottom of the plant, overlapping slightly, as you move up to the top of the first branches. Do not use any wires, ties, rope or tape around the trunk – you do not want to accidentally injure the bark.

If the ground does not have snow cover or mulch, the freezing and thawing of the ground occurring predominately during the beginning and end of the cold season can cause soil heaving. The expansion and contraction of the soil forces newly planted shrubs and perennials out of the ground, then partially back down, then up again exposing the roots to cold damage and potentially breaking them.

To manage soil heaving, apply a 2-4 inch layer of mulch to the ground around the trees, and shrubs and/or perennial beds after the ground freezes if it was not applied in the spring. The idea is to keep the soil temperature constant during the cold weather. Keep the base of the tree or shrub clear of mulch so that you can notice feeding damage from small animals such as mice, voles or rabbits. Evergreen boughs can also be used to cover the soil to protect against soil heaving. Planting trees and shrubs in the spring gives them the advantage of a whole growing season to get their roots established. If new plants are uprooted by soil heaving, have a bucket or large container of unfrozen soil and mulch handy to replant and mulch the uprooted plants. This action can give the plants a chance of recovery.

“Winter Burn” is another frozen ground related problem landscape plant encounter if there is not enough moisture in the soil below the ground for the roots to uptake. The leaves of conifers and broadleaf evergreens are desiccated. The needles or leaves turn brown at the tips first and depending on the severity of the injury, the damage spreads further on the leaf surface. Evergreen plants can also be desiccated by cold dry winds drawing moisture from the leaves. Products called anti-desiccants can be applied to broadleaf evergreens and conifers when the plants are dormant. Applying too soon may trap excess water in the leaves that can freeze and burst. Follow the label instructions. The label may recommend applying when temperatures are between 40o and 50oF.

Planting evergreens on the north, north-east or east side of buildings will provide some protection from sun and

Closer view of winter-damaged cherry laurel. Note the shot holes. Photo: Richard Buckley, Rutgers PDL drying winds. Barriers around the plants can be made with wooded frames covered with burlap or canvas. Keep the top and bottom of the barriers open as you do need some air circulation around the plants.

If winter damage has occurred there are a few things you can do to help plants recover, keeping in mind that some plants will be able to recover better then others. Plants that do not survive can be replaced with plants that are better suited to the environment. Select plants that are hardy in USDA temperature zones for New Jersey (7a, 7b, 6a or 6b) depending on the location. Plants that begin growth and flower later in the spring and go dormant earlier in the fall do better in colder areas. To help plants recover, prune out dead branches and stems. Resuming watering and applying fertilizers in the spring based on a soil test result will also aid in the plants’ recovery from the winter. Next fall, you will be prepared to protect the landscape from cold injury.

Madeline Flahive DiNardo is the County Agent / Associate Professor with Rutgers Cooperative Extension of Union County. Madeline works with volunteer Master Gardeners and provides training programs for county park employees and landscape professionals, such as the Rutgers North Jersey Ornamental Horticulture Conference.

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