Winterize Those Trees and ShrubsBy Paul Rodman (paulgrow)
October 17, 2012
Trees and shrubs are investments that require a small amount of care. For the sake of your tree's quality of life and your own, take a few minutes to winterize your trees and shrubs. Beautiful springs come from well-tended winters. Here are some tips to help you make sure your trees are ready for winter.
1. Remove visible damage and dead wood. Try to make small pruning cuts that minimizes the exposure of the central heartwood on the branch.
2. Prune branches that will touch the ground when loaded with rain and snow. Foliage and branches that are in contact with soil can invite undesirable pests and problems.
3. Remove damaged and declining twigs, branches, and bark. Do not leave food and shelter for pests during the winter.
4. Remove any sprouts or suckers growing at the tree base or along stems and branches. Pruning should conserve as many living branches as possible with only a few selective cuts.
5. Spread a thin layer of organic mulch to blanket the soil. Cover an area at least as large as the branch spread. Mulch is nature's way of recycling valuable materials, but be careful of pests hitching a ride.
6. Properly wrap new trees that have not developed a corky bark and could be easily damaged. Injury from the environment, including chewing and rubbing by animals, must be prevented.
Tree warap will protect
against wind and animals
7. Aerate soil if it is compacted and poorly drained. It is critical not to damage tree roots in the soil. Saturated and dense soil can suffocate roots.
8. Fertilize with all the essential elements, if they are in short supply within the soil. Be sure to go lightly with nitrogen, especially under large, mature trees and around newly planted trees.
9.Watering may be needed where soils are cool but not frozen, and there has been little precipitation. Winter droughts needs treatment with water the same as summer droughts, except it is much easier to over-water in winter.
There are several conditions that you need to be on the lookout for.
Sunscald, also called southwest injury, develops on the south and southwest sides of the trunk or on the upper surfaces of limbs exposed to sun, particularly in thin-barked trees like maple, young crabapples, flowering fruit trees, and mountain-ash. Usually, a pre-existing injury exists on the side where the damage develops. The temperature under the bark of south to southwest facing trees can reach into the 60-degree range while the shaded portion remains at freezing (32° F). Damage to the cambium layer (the thin, formative layer beneath the bark of the tree that gives rise to new cells and is responsible for secondary growth) can result in dieback or even death. This heating results in the tree losing its dormancy, which is followed by freezing when the sun sets. Sunscald, coupled with drought, can result in vertical frost cracks and death of the cambium layer. Frost cracks also provide an infection point for decay and pathogens. Prevention is the best method for contending with sunscald. If possible, provide shade by strategically placing other plants or structures on the south sides of thin barked trees and shrubs. Tree wrapping with reflective or light-colored material may be effective in preventing sunscald and bark cracking.
The current recommendation for newly planted, thin bark trees is that they should be wrapped for at least two winters or until mature bark is established.
Regardless of how many winters you wrap your trees, care must be taken to remove the wrapping in the spring to prevent moisture from collecting between the bark and the wrapping. During the spring, wrapped bark may provide an infection point for disease when the weather warms up.
Winter ice storms create a hazard to plants as well as people: The formation of a heavy glaze (more than a half-inch thick) breaks twigs, branches, and trunks or can even uproot trees. Damage increases if ice storms are associated with heavy winds, and can result in additional breakage. Fast growing trees with brittle wood (Cottonwood, chinese and Siberian elms, poplars, silver maples, boxelders, birches and willows) are predictable victims of ice storms due to the brittle wood they possess. Elms seem particularly susceptible to ice damage as brittle wood is coupled on a tree with wide branch angles.
Management of Winter Injury
Many popular trees such as red and white pines, maples, and lindens, along with the non-native Colorado blue spruce, English hollies, and mountain-ash, are more vulnerable to winter injury native, locally adapted plants. Avoid planting those species or cultivars that are unusually susceptible to winter damage. Although occasional winter damage is a fact of life for most trees, winter damage that occurs consistently will weaken trees and predispose them to potential insect pests and disease. Adequate watering, fertilizing and mulching to improve tree vigor protects the tree from winter damage or minimizes the impact of such damage when it occurs. Winter damage is unsightly, but is rarely fatal. With the proper protection and a little patience, your trees will recover their healthy green after the last red needles fall.
Winter burn is a common occurrence to evergreens, including boxwood, holly, rhododendron, and most conifer species. Winter burn symptoms often develop when temperatures warm-up in late winter and early spring, and is often misdiagnosed as an infectious disease or damage from excessively cold temperatures. Winter burn is caused from desiccation, which is a type of dehydration injury. Dehydration and winter burn results when roots are unable to obtain water lost through transpiration. Water loss through transpiration is normally low during winter months, but it increases when plants are subjected to drying winds or are growing in warm sunny spots.
Winter burn causes the scorching of leaf tips or outer leaf margins, complete browning of leaves and needles, or browning from the needle tips downward, or death of terminal buds and/ or twigs.
Several techniques to minimize or prevent winter burn can be implemented, with varying degrees of success:
- Carefully choose planting materials, avoiding trees and shrubs that are known to suffer from winter burn (including Alberta spruce, English holly and Colorado blue spruce),
- Avoid planting broadleaved evergreens like rhododendron in areas of high wind exposure,
- Deep water plants before ground freeze, and continue to water during winter months when temperatures remain above freezing but without precipitation,
- Erect physical windbreaks.
- Wrap problem plants with burlap or other material to protect from wind and subsequent moisture loss to evergreen shrubs and small trees.
- Various types of antitranspirants such as Wilt-Pruf are available, but have shown limited success. These are very short-lived and must be reapplied every 2 to 3 weeks to remain effective.
A Burlap screen can prevent
Winter Discoloration of Evergreens
Browning or bleaching of evergreen foliage during winter occurs for four reasons:
1. Winter sun and wind cause excessive transpiration (foliage water loss) while the roots are in frozen soil and unable to replace lost water. This results in desiccation and browning of the plant tissue.
2. Bright sunny days during the winter also cause warming of the tissue above temperature which in turn initiates cellular activity. Then, when the sun is quickly shaded, foliage temperature drops to injurious levels and the foliage is injured or killed.
3. During bright, cold winter days, chlorophyll in the foliage is destroyed and is not resynthesized when temperatures are below 28° F. This results in a bleaching of the foliage.
4. Cold temperatures early in the fall before plants have hardened off completely or late spring after new growth has occurred can result in injury or death of this non-acclimated tissue.
Foliar damage normally occurs on the south, southwest and windward sides of the plant, but in severe cases the whole plant may be affected. Yew, arborvitae, and hemlock are most susceptible, but winter browning can affect all evergreens. New transplants or plants with succulent, late season growth are particularly sensitive.
Last but not least, winter is the ideal time to prune oak trees. Oaks are susceptible to attack by the oak beetle as well as a disease called oak wilt. Both the insect and disease enters the tree through fresh cuts made by pruning. By doing this in the wnter you can protect your tree against against these threats.
By spending a little time now preparing your trees and shrubs for winter will result in healthy trees and shrubs in the spring.
Photos courtesy of Purdue University Extension