Stop the burn
Did you notice browned areas on your evergreens at the end of last winter? You may still be able to do something to prevent a repeat performance of this condition, winter burn, which happens when evergreen leaves lose too much water in winter.
No need to worry about deciduous trees and shrubs in winter because, without leaves, they lose little moisture.
Stop leaves from losing water
Antitranspirants, also called antidesiccants, are materials that slow water loss from plant leaves. (“Wilt-Pruf” is a common brand, but there are others.) Sprayed on leaves, these materials help plants when their roots can’t take up enough water to replace that lost from leaves.
Evergreens sometimes find themselves in this thirsty predicament in winter, especially when bright sun, wind and temperatures above freezing suck water out of the leaves, yet the soil remains so deeply frozen that roots can’t absorb sufficient moisture.
To protect a plant in winter with an antitranspirant, spray the leaves in late fall and then again toward the end of winter. Spray only when temperatures are above freezing, and wash out the sprayer with warm, soapy water immediately after application.
Antitranspirants can also help preserve the foliage on evergreen branches cut for vases and on Christmas trees. Because they actually coat leaves, antitranspirants have also reduced the incidence of certain diseases, such as downy mildew on zinnia, and black spot and powdery mildew on roses.
Leaves have to breathe
I’m not recommending dousing your winter landscape in antitranspirant sprays. Some cautions are in order. Those same pores through which leaves lose water also draw in carbon dioxide for photosynthesis. Plants get their energy from the sun with photosynthesis, so they could be weakened by these sprays.
Unfortunately, antitranspirants are generally more hazardous to evergreens, which need them more, than to deciduous plants.
Never apply antitranspirants to blue spruces or other plants with bluish, waxy coatings on their leaves. That waxy coating is the plant’s own, natural antitranspirant. Spraying an antitranspirant washes away the wax and the blueness.
Minimize toxic effects from antitranspirants by reading the label carefully, noting cautions with respect to certain plants, and following directions as to dilution and timing.
Other greening measures
A few other measures besides or in addition to spraying an antitranspirant can help your evergreens avoid winter burn. If the soil is very dry in autumn, water. Stationing yourself in front of your evergreen spraying the ground with a hose-end sprayer won’t do it; the plants will need about 2 gallons for every square foot of estimated spread of their roots.
Mulching the ground in autumn also helps by conserving moisture in the soil and maintaining a warmer soil temperature to a greater depth. Roots are more active in warmer soil, and less frozen water means more water available to roots.
When planting an evergreen, site it to lessen chances of winter burn. Drying winter sunlight will beat down on evergreen leaves backed by a south-facing wall or reflected off concrete or other paving.
But also keep that antitranspirant handy in your quiver of techniques to avoid winter burn of evergreens.