You’ve removed late-autumn weeds, layered on the mulch, pruned appropriately, possibly even covered or wrapped your plants – so why do some still die in the winter, despite all your well-meaning efforts?
Many plants die during winter because they dry out, or desiccate. As temperatures drop, the ground freezes and plant roots cannot take water from the soil, no matter how much snow may fall. This causes the plant to use stored water from the leaves and stems as part of the transpiration process, during which water exits the plant through the leaves. If the sun is shining or the wind is blowing, transpiration increases and more water exits the leaves. If no water is available and transpiration continues, the plant will soon die. Because evergreen plants do not drop their leaves, they are especially susceptible to this death.
Preventing Desiccation
How can you help your plants stay well-hydrated through the frozen drought of winter? The first step is to remember healthy plants in the summer survive the hardships of winter far better than sickly or stressed plants. Through the spring, summer and fall, you should always be on the lookout for signs of pests, diseases and damage, and take all necessary steps to keep your plants thriving.
Second, be sure to water well even when temperatures begin dropping below freezing. Later, if the ground thaws, water before the ground refreezes. Water slowly to provide a deep drink without waterlogging the roots, however, so they are not damaged by ice.
The third step is to use an anti-desiccant, also called an anti-transpirant, to reduce the moisture loss from the leaves and needles. Because broadleaf evergreens such as boxwood, aucuba, holly, rhododendron, many laurels, Japanese skimmia and leucothoe do not drop their leaves, they are especially vulnerable to winter death. Using a product such as Wilt-Pruf to reduce transpiration by protecting the pores will save many broadleaf evergreens.
When using any horticultural product, be sure to check the label and follow all instructions properly. Some conifers such as cedar, cypress, juniper and pine may benefit from these products. However, be sure to read the instructions to prevent burning specific conifers. Also, do not use on “waxy” blue conifers, such as blue spruce, which already have an oily protective film on the nettles.
Here are a few reminders to get the best protection from an anti-desiccant:
- Plan to apply when day temperatures begin dropping below 50⁰ Fahrenheit. Apply when temperatures are above freezing on a dry day with no rain or snow anticipated within 24 hours. This allows the product to thoroughly dry. Spraying in freezing temperatures will cause plant damage.
- Do not spray conifers until thoroughly dormant, generally in late winter. This prevents trapping moisture in the needles which could burst when frozen.
- Generously apply to dry leaves and needles. Don’t forget the undersides. Spray from several angles to ensure complete coverage.
- Because the anti-desiccant will break down in light and warmth, reapply in late winter on a dry day when temperatures are above freezing for at least 24 hours.
Beyond Winter Drought
Other than protecting your landscape evergreens from winter drought, there are other uses for anti-desiccants. Many gardeners use it to protect newly transplanted shrubs from drying winds and sunshine as they settle in. It also provides protection to tender bulbs going into storage. A quick spray in early winter protects rose canes and hydrangea stems. Spraying onto live or cut Christmas trees and carved pumpkins slows the drying process, making them last longer for greater holiday enjoyment.
