Mulch offers many benefits to plants during the growing season and it is equally important to mulch plants over the winter.
You may think that the purpose of winter mulch is to keep your plants warm but it is actually just the opposite. Mulch should be applied after the ground freezes, usually around Thanksgiving. Its purpose is to keep the ground frozen rather than allowing it to freeze, then thaw on a warm day, then freeze again. The freeze/thaw cycle can damage the roots of a plant or even heave it out of the ground. This exposes their roots which will be killed by the cold. It is especially important to mulch young trees and shrubs and newly planted perennials over their first winter since they are not firmly established in the ground.
The recent warm winters make mulching even more important as we cannot count on consistent cold temperatures to keep the ground frozen. In the past, a blanket of snow provided the best mulch, but the snow cover is no longer constant throughout the winter so we have to provide the mulch ourselves.
Any plants that are overwintered outdoors in containers should be mulched thickly. Not only is the top of the container exposed to the sun, but the sides, especially if they are dark in color can really warm up on a sunny winter day.
A 2- to 6-inch layer of organic mulch placed around perennial flowers, trees and shrubs is best. For trees, it should be spread all the way to the drip line, the circle covered by the outermost branches, as small feeder roots may extend this far. Do not lay mulch right up to the stems or trunks of the plants. This just encourages mice and moles to snuggle up under the mulch and make a winter snack of the plants.
Winter mulch should be of a material that doesn’t pack down with the weight of snow or heavy rain. Hay, straw and pine needles are good. Evergreen branches cut from your Christmas tree make a great mulch Leaves will pack down unless something waterproof is placed on top of them. If you use wood chips or bark as a landscape mulch, replenish them now and make them do double duty as a winter mulch. Not only will you get the benefits of winter mulch, you’ll be that much further ahead in your spring chores!
A final benefit of winter mulch is that it prevents the soil from warming too rapidly in the spring. When the soil warms too quickly, shrubs and trees are fooled into leafing out and blossoming too early, thereby exposing themselves to frost damage.
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