MSU Extension Gardening in Michigan

After last year’s devastating winter, people may be wondering what they should do to protect their landscape plants this winter. Here are some points to consider:

Keep soil evenly moist throughout the growing season. Moist soils will hold more heat than dry soils and are less subject to frost penetration than dry soils. Keeping plants sufficiently watered throughout the growing season will result in better root growth and healthier plants going into winter. Even if plants are well-established, be sure to give them a good drink of water in late fall before the ground freezes and maintain a 3-inch layer of organic mulch around the trees or shrubs. Additional mulch through the winter (another 1-3 inches) for recently planted trees and shrubs can help encourage root growth in fall and reduce root injury from frost penetration into the ground. Avoid placing mulch directly against the trunk, and remove the extra mulch layer in spring when growth resumes.

Location, location, location. Plant marginally hardy plants in protected locations in your landscape. Avoid planting in areas that receive heavy loads of deicing salts. When shoveling salty snow, avoid piling it around landscape plants where it will accumulate and be absorbed by roots. A well-constructed burlap screen (see below) can help protect plants subject to salt spray from passing traffic. Fix downspouts that leak and clean gutters of leaves before winter sets in. Plants beneath these areas can be damaged by heavy deposits of ice.

Winter desiccation. Winter sun and wind causes the foliage of evergreen foliage to lose moisture that is not replaced while the roots are frozen. Some plants are more susceptible than others including evergreens with short needles, such as Alberta and Serbian spruce, hemlock, yew and arborvitae, and broadleaf evergreens, such as boxwood and rhododendrons. The sides of plants exposed to wind, along with the sides most exposed to sun (typically the south and southwest) are most subject to winter injury of this type. Directions for building a sturdy windscreen can be found in “Build a better windscreen for your evergreens this winter” by Michigan State University Extension.

A summary of directions for creating a windscreen follows: Use posts designed for temporary electric fencing of livestock to form the supports for the screen. Install the posts in October before the ground freezes. Install the stakes far enough away from the plant that they do not touch. The best choice of stakes is the slender posts used for temporary electric fencing for livestock. At least four posts per plant are needed. Surround the posts with a cylinder of chicken wire, hardware screening, welded or woven wire farm fencing. Overlap slightly and wire the ends together. Pick a calm day in November or December to add the layer of burlap. It should also overlap. Secure the burlap to the fence with wire bag ties or wire twist ties. Place them high, low and in between. Make sure the top is open and the bottom burlap is snuggled into the mulch for more stability.

The windscreen can remain in place until early to mid-March. Posts can remain until the ground thaws. This windscreen also helps prevent animal damage, especially if the wire is hardware screening. When this wire is pushed into the ground, it deters entry by voles and rabbits. If deer are a problem, crisscross wire or heavy string over the top of the cylinder so deer can’t lean in and chew the tops of plants.

Injury to thin-barked trees. Sunscald, sometimes referred to as southwest injury, can occur on cold, sunny, winter days. Bark heats up to the point that cambial activity resumes, then the temperature of the bark drops rapidly when the sun is blocked by a cloud, or when it drops behind a barrier such as a hill. The quick drop in temperature kills the active tissue. To prevent sunscald, wrap the trunk with a commercial tree wrap, plastic tree guards, or use white latex paint to reflect the sun and keep the bark at a more constant temperature. If using tree wrap, put it on in the fall and remove it in the spring after the last frost.

Leaving tree wrap on year-round is not recommended as it provides a good location for certain trunk boring insects to hide and cause damage. Newly planted trees should be wrapped for at least two winters and thin-barked species up to five winters or more. Areas of the trunk damaged by sun scald should be carefully trimmed back to live tissue with a sharp knife, following the general shape of the wound, rounding off any sharp corners to facilitate callusing of the wound.

Frost cracks may also occur when the south or west side of a tree is heated by the sun. The bark and inner wood expands when warmed by winter sunlight. Once the sun sets or is hidden by clouds, temperatures of the bark drop quickly, causing the bark to shrink. It takes longer for the inner wood to contract. The unequal shrinkage between the bark and the inner wood causes the bark and the wood directly beneath it to split. Once the cracks have occurred there is little that can be done.

While it can be worth the time and effort to protect a few specimen plants in the landscape, it’s better to have mostly plantings that can survive without extra pampering. Take the time to make sure that plants in your landscape have been installed in the right location, and you will have fewer worries about winter protection. If the same plants prove troublesome year after year, it might be worthwhile to either find then a new home in your landscape where less protection will be required, or replace them all together.