Winter mulching of plants is an important process where perennial plants are concerned. Annuals die every year, so mulching them for the winter is not necessary. Different materials can be used to mulch plants for the winter, some of which gardeners may already have on hand without need to spend additional money.
Winter mulching of plants helps conserve moisture in the roots of tender perennials as the weather dries out. It also serves to protect tender plants from the extremes of frost and thaw as the climate cycles over the course of the winter. Extremely warm thaws can trick plants into coming out of their dormancy. When the next freeze occurs, tender new growth can be severely damaged or even killed. Winter mulch prevents this from happening.
Winter mulch should be applied after plants have gone dormant for the winter. Applying it sooner prevents plants from fully going dormant for the winter. Mulch helps keep soil temperature constant. Concerned gardeners should pay attention to their local weather forecasts. Perennial plants should undergo two to three hard freezes before gardeners apply mulch. Hard freezes occur when temperatures slip below 25 degrees Fahrenheit.
Winter mulch can be made of straw, dead leaves or even old evergreen needles and branches. Gardeners should use whatever they have available to insulate their perennial plants over the winter. It is not necessary to purchase wood chips or other mulch from garden centers unless other options are unavailable. Snow forms a sort of mulch as well, but since it is impossible to know exactly when snow will fall, gardeners should not count on it in their calculations.
Winter mulch is not applied in order to protect perennial plants from freezing. Instead, it is applied to help retain moisture and to keep soil temperature constant through winter's freeze and thaw cycles. Applying mulch too early will prevent perennials from the freeze they need in order to go into full winter dormancy, according to Kansas State University Research and Extension horticulturist Dennis Patton.
Most perennial plants need a 1 to 2 inch gap between the mulch and the plant crowns/stems. Allowing this gap helps guard against the possibility of damage to tender stems and crowns as the mulch decomposes. One exception is grafted roses, which should be mulched with six inches of soil that are then covered with straw or dead leaves.