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Anti-desiccants stave off winter water loss in rhododendrons, mountain laurels

| Saturday, Nov. 17, 2012, 8:57 p.m.

Q: I wondered what you think of Wilt-Pruf and other products, specifically for use on rhododendrons and mountain laurels in the winter.

A: Anti-desiccants, like Wilt-Pruf and other brands, are meant to stave off water loss through the winter months and during times of stress. They work by “sealing” the tiny pores on a leaf's surface and thereby preventing water vapor from exiting through them.

Because their leaves are large and they remain intact through the colder months, the winter is particularly difficult on broad-leaved evergreens such as rhododendrons, mountain laurels, boxwoods, azaleas and hollies. The bigger leaves on these plants have many leaf pores, which makes them more prone to drying out in winter winds. This is especially true if we do not get any precipitation for long periods of time or if the ground remains frozen and water is unavailable to them.

Spraying broad-leafed evergreens like these with an anti-desiccant product will indeed help prevent the symptoms of dehydration, including leaf browning, winter die-back and curled leaves. Anti-desiccants are best applied to upper and lower leaf surfaces on a day where temperatures are above freezing and rain is not predicted for twenty-four hours. Read the label well before use, as these products cannot be used on certain plants without causing issues with leaf discoloration and leaf drop. Apply only to the plants specified on the label.

Because anti-desiccants break down as the winter progresses, a second mid- or late-winter application is a good idea. Choose a day that is well above freezing and when the weather is predicted to stay above freezing for a day or two.

If you don't want to go the anti-desiccant route, but are interested in protecting your broad-leafed evergreens from winter dehydration, be sure to keep all your trees and shrubs well watered through the winter months. This is especially true for newly planted or transplanted specimens. Add any necessary supplemental irrigation on warmer days when the top few inches of soil are less likely to be frozen and the water can soak in.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.

Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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