Yard and Garden: Prevent Winter Injury to Trees and Shrubs



AMES, Iowa — Giving trees and shrubs some extra attention in the fall will help them over-winter and start spring in peak condition. Horticulturists with Iowa State University Extension and Outreach explain certain practices homeowners can use to significantly reduce winter damage to trees and shrubs. To have additional questions answered, contact the Hortline at 515-294-3108 or hortline@iastate.edu.

How do I prevent desiccation injury to my yews and boxwoods? 

Narrow and broadleaf evergreens lose considerable amounts of moisture through their leaves or needles, buds and stems during the winter months. The loss of water is mainly due to strong winds and sun. Once the ground freezes, however, plant roots are no longer able to absorb water. Plant foliage that loses a large amount of moisture may eventually dry out, turn brown and die. The damage to the needles/foliage is referred to as desiccation injury or winter burn. While desiccation injury occurs during the winter months, damaged needles/foliage often retain their green color until late winter or early spring.  

To prevent desiccation injury, deeply water susceptible narrow and broadleaf evergreens in fall if the soil is dry. Continue watering on a regular basis until the ground freezes in winter. Watering is especially important to evergreens planted in the last two to three years. Moisture loss can be reduced by erecting a shield or screen to deflect drying winds or shade plants in winter. A simple screen can be constructed with wooden posts and burlap. Applications of an anti-desiccant to susceptible evergreens may also be helpful.

How do I prevent rabbits from damaging trees and shrubs in winter? 

The most effective way to prevent rabbit damage to trees and shrubs in the home landscape is to place chicken wire fencing or hardware cloth around vulnerable plants. To adequately protect plants, the fencing material needs to be high enough that rabbits won’t be able to climb or reach over the fence after a heavy snow. In most cases, a fence that stands 24 to 36 inches tall should be sufficient. To prevent rabbits from crawling underneath the fencing, bury the bottom 2 to 3 inches below the ground or pin the fencing to the soil with u-shaped anchor pins. Small trees can also be protected by placing white plastic tree guards around their trunks. Since the weather in late fall in Iowa is unpredictable, it’s best to have the protective materials in place by early to mid-November.

After a heavy snow, check protected plants to make sure rabbits aren’t able to reach or climb over the fencing or tree guards. If necessary, remove some snow to keep rabbits from reaching the trees or shrubs. 

How can I prevent damage to trees and shrubs from deicing salts? 

Homeowners can minimize salt damage by using deicing salts prudently. Before applying salt, wait until the precipitation has ended and remove as much of the ice and snow as possible. Use deicing salts at rates sufficient to loosen ice and snow from driveways and sidewalks, then remove the loosened ice and snow with a shovel. (Deicing salts need to be applied at much higher rates to completely melt ice and snow.) Mix salt with abrasive materials, such as sand or kitty litter. Fifty pounds of sand mixed with one pound of salt works effectively. Avoid piling salt-laden snow and ice around trees and shrubs.

While the amount of salt applied to major roadways cannot be controlled, steps can be taken to minimize damage. As soon as the ground thaws in early spring, heavily water areas where salt accumulates over winter. A thorough soaking should help flush the salt from the root zone of plants. If possible, alter the drainage pattern so winter run-off drains away from ornamental plants.

When planting trees near major streets or highways, select salt tolerant tree species. Bur oak, northern red oak, honey locust, northern catalpa, Kentucky coffee tree, horse chestnut and eastern red-cedar are salt tolerant tree species.  

2014 Garden Calendar is the Wonder of Trees

The 2014 Iowa State University Extension and Outreach garden calendar celebrates the wonderful gifts that trees provide for other living things. In addition to striking photos, find monthly garden tips, tree-planting instructions, Iowa's state forests, vignettes of historical trees and quotes that trees inspired.

The 2014 garden calendar can be purchased at the Extension Online Store https://store.extension.iastate.edu/.
 

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