The best winter protection for trees and shrubs, wherever they grow, is proper care during the growing season. The healthier they are before the cold weather arrives, the better their chances of coming through the winter safely. Feed your plants with an all-purpose slow-acting granular fertilizer in late fall to encourage root development and nutrient storage without stimulating unwanted foliage growth.
Mulching the soil and deep watering shrubs and perennial flowering plants very well–usually in October or November–are important protective measures. In this instance a soaker hose or drip irrigation system, run for several hours around every tree and shrub, does the best watering job. With plenty of moisture in their tissues, plants are better able to withstand drying by harsh winter sun and wind.
Dealing with Winter Winds
Cold winter winds threaten plants, especially evergreens, because they pull moisture from leaves and soil. When plant roots can not replace this lost moisture, leaves and twigs shrivel and die. Mulching and deep watering are good preventives.
Loosely wrap natural burlap with openings at the top and bottom for air circulation around plants to protect them from wind. Never cover plants with plastic sheeting.
Erect a simple windbreak to block the wind. Nail lengths of burlap, wind screening fabric or heavy-duty polyspun floating row cover to wooden stakes and drive them into the soil to create a screen on the windward side of the plant.
Make portable folding A-frame shelters out of sheets of plywood, wood slats or snow fencing that can be stored away until next winter.
Spray needled and broadleaf evergreen foliage with an anti-transpirant spray product which reduces evaporative moisture loss by up to 80% while still allowing gas exchange. Follow label instructions.
Dealing with Frost Heaving
Repeated freezing and thawing of the ground sometimes heaves the soil, disturbing plant roots and shallowly planted bulbs. A winter mulch layer of 3 or 4 inches of organic material such as wood chips, pine boughs, bark mulch, or even old newspapers, insulates the soil, moderating temperature fluctuations. For best results, apply the mulch after the first hard freeze.
Winter mulch is not intended to prevent the soil from freezing, but to keep its temperature more uniform, especially during winter mild spells. It also delays soil warming in spring, so shrubs and trees do not bloom so early that their spring blooms are caught by a late frost. Because feeder roots of many trees and shrubs spread some distance from the trunk, spread the mulch in a circle from the trunk to at least their dripline. Keep mulch away from tree trunks to prevent rodent and disease problems.
Dealing with Sudden Freezes
Plants handle very cold winters with lots of snow cover better than milder winters punctuated by sudden or extreme temperature changes. A warm spell in late winter can cause serious damage if it encourages leaf and flower buds to develop. When the temperature drops again, the moisture-filled cells rupture, often killing the plant.
Freezing damage most commonly occurs in the fall or spring, when green wood (new growth) or blossoms are susceptible to sudden frost. The best way to deal with this unpredictable problem is to grow plants, shrubs, and trees known to be cold hardy in your region.
Dealing with Sunscald
Sunscald may sound like something that happens in hot weather, but it is a cold-weather problem, occurring in winter and early spring. It is often evident on young, thin-barked trees planted where daytime temperatures are high, such as beside a wall that reflects the sun’s heat. Tender bark on the south facing side of the trunk or stem warms much more than the north facing side. For this reason, sunscald is sometimes called “southwest disease.”
On a relatively warm day, bright sun is absorbed by dark-colored tree trunks and start the sap flowing. If a severe freeze occurs that night, the bark may split. The wound may extend 1 to 6 feet down the side of the trunk and be an inch or more wide, an obvious invitation to pest insects and fungi. Minimize sunscald by watering thoroughly before the ground freezes, and by wrapping trunks of vulnerable trees with a commercial tree wrap product. Another way to guard against early-spring sunscald is to spray the bark on the south side of young trees with white latex paint in the fall. The light color reflects the sun’s rays and lowers bark surface temperatures by at least 10 degrees.