These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.
Snow, Cold & Landscape Plants
December 16, 1999
Even though we have advanced halfway through December, significant snows and bitter cold have stayed away so far. There is plenty of winter left for this to change, but how does snow and cold affect landscape plantings?
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. So far in December, we have been seeing the soil surface freeze at night but then thaw with the mild days. If you have not yet mulched perennial beds, it would be suggested to do it soon. Straw and evergreen boughs are good choices.
The mild weather so far has made it easy on trees and shrubs. For the sake of the plants, a gradual transition into bitter cold would be best, rather than a quick extreme temperature drop. Prolonged periods of near zero or below zero temperatures can injure many trees, particularly those marginally hardy for our area. Buds, twigs, and entire branches may be killed. In spring, typical 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 in winter may cause desiccation injury to plants. Above ground plant parts to dry out because water cannot be replaced from frozen soil. Since fall has been rather dry, this injury is likely. Evergreens of all types are most susceptible, including needle evergreens (yews) and broadleaf evergreens (rhododendron, boxwood).
Commercially available anti-transpirants can be sprayed on susceptible plants in late fall (temperatures above freezing) to help prevent drying out. As mentioned over the past few weeks, adequate watering of plantings throughout the fall is a key to preventing this damage.
Another consideration concerning winter weather is the effect on pests. Sub-zero temperatures can be brutal on us but also on some insects. Gypsy moth, currently increasing as a problem in our area, is favored by mild winters because it overwinters as egg cases susceptible to damage in subzero temperatures.
Voles, which can damage tender bark of trees and shrubs along with tunneling
across the surface of lawns, cause more problems when there is snowcover
to provide shelter from predators. Rabbits also tend to cause more damage
to trees and shrubs when there is extensive snowcover.