When harsh winter winds beat against evergreens, or there is an unseasonably warm, sunny day, moisture evaporates out of the leaves. Because the ground is frozen, water cannot come up from the roots to replace what is lost. This dehydration is a major cause of winter burn, which causes die-back in evergreens, especially the broad-leaved ones. That is why I have become a fan of antidessicants.
An antidessicant (anti-transpirant) is a spray that coats the leaves and prevents or diminishes the loss of moisture. On the other hand, it limits the uptake of carbon dioxide. So this is not something to use indiscriminately. But for plants that are vulnerable to winter burn or are at the edge of their hardiness zone, I have found them to be beneficial.
I apply them in late fall, usually in December, before the extreme cold and dry winds of mid-winter. Wilt-Pruf (www.wiltpruf.com) is a brand you can find at nurseries and garden centers to apply yourself. I currently pay my arborists to spray a large group of shrubs each year. The Care of Trees (www.thecareoftrees.com) is a regional company that offers organic and eco-friendly plant care. I find that their employees do care about trees and plants and work carefully and respectfully when pruning, spraying, etc.
While my many Rhododendrons are technically hardy in this Zone 6 location, they have suffered severe winter burn some years. The west wind that crosses my property can be very destructive in winter and dries out the broad-leaved evergreens. Though they naturally defend themselves by curling their leaves in extreme cold, this is not always enough. Since I began spraying them with the antidessicant, they have come through the winter in much better shape. This is important because the stress of winter burn is an invitation to other ailments.
I have also taken to spraying many of my Hydrangeas—Nikko Blue and Blue Wave (H. macrophylla), Oakleaf (H. quercifolia), and Serrata (H. Serrata). These deciduous shrubs are also rated hardy for my location, but several flowerless (and miserable!) years taught me that the cold, wind and frequent freeze/thaw cycles of our winters can destroy the flower buds which are formed the previous season. I tried several years of surrounding the hydrangeas with burlap enclosures. This worked to ensure good blooming, but what a nuisance and eyesore it was! The antidessicant spray is far easier, invisible, and, so far, equally effective. Preferably, the Hydrangeas should be sprayed after they lose their leaves for better coverage.
At right is the delicate bud on a Hydrangea macrophylla 'Blue Wave.' that has to survive the winter.
I do not need to spray my Limelight Hydrangea (H. paniculata ‘Zwijnenburg’Limelight) because it blooms on new growth from the current year. So it is worth checking whether your hydrangea blooms on new or old growth to see if it is susceptible to winter damage.
Finally, since I have just planted a precious Magnolia grandiflora this season (see earlier post), and it is marginally hardy here, I will have that sprayed, too, for insurance.Tags: freeze/thaw cycles, The Care of Trees, evergreens, broad-leaved evergreens, burlap, winter damage, Rhododendrons, Nikko Blue, Blue Wave, Hydrangea quercifolia, Hydrangea serrata, Hydrangea paniculata, Hydrangea Limelight, Hydrangea macrophylla, Wilt-Pruf, antidessicant, winter burn, Winter Read More