University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Upcoming Winter Weather and Plants

November 29, 2001

With winter on the horizon, a variety of forecasts are made as to precipitation and temperature expectations. While it is difficult to predict the actual weather winter may bring, predictions can be made as to the effect of various conditions on landscape plants.

November has been quite mild. For tree and shrub health, a gradual transition into bitter winter cold would be best, rather than a quick extreme temperature drop. Drastic fluctuations and prolonged periods of subzero temperatures can injure many trees and shrubs, particularly those marginally hardy for our area. Buds, twigs, and entire branches may be killed. Next season low temperature injury may show up as the lack of flowering, or a plant appearing to resume normal growth and then suddenly wilting and collapsing.

In addition to bitter cold, winds of winter may cause desiccation injury to plants. Above ground plant parts to dry out because water cannot be replaced from frozen soil. Evergreens of all types are most susceptible, including needle evergreens (yews) and broadleaf evergreens (rhododendron, boxwood). Most areas have had adequate rainfall this fall, which helps decrease injury potential, but winter conditions will dictate what damage may occur.

While opinions vary on the desire for snow, significant snow cover provides excellent insulation of the soil. This helps protect perennials, bulbs, ground covers, and strawberry plantings from alternating freezing and thawing cycles that can lead to soil heaving. This is the major reason winter mulches are put over perennials and related plantings. Straw and evergreen boughs are good choices for mulching beds in the upcoming weeks.

Finally, winter weather impacts pests. Subzero temperatures can help reduce some insects, such as those overwintering as egg masses on trees. Snow cover provides shelter from predators for pests such as voles (field mice), which do damage to lawns. Rabbits also tend to cause more damage to trees and shrubs when there is extensive snow cover.


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