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Volume 15, Issue 50 ~ December 13 - December 19, 2007

Keep Your Shrubs Watered in Winter

Chemicals can’t replace good old TLC

Now is the time of year when advertisements urge you to spray plants with anti-desiccants or anti-transpirants to protect foliage during the winter months. The theory is that these materials seal the surface of the leaves to keep in moisture. The concept may seem sound, but repeated testing has clearly demonstrated that it doesn’t work.

Plants control the amount of water leaves lose by either rolling their leaves — as is commonly seen with rhododendron, acuba and other broadleaf evergreens — or by closing stomates, which are small openings on the undersides of leaves. Stomates allow carbon dioxide to enter the leaf tissues and aid in photosynthesis. When an excess amount of water is lost to the atmosphere, the stomates are closed by guard cells.

Many researchers — I am one of them — have tested anti-desiccant products and come to the same conclusion: They do not work and have the potential to do more harm than good.

Stomates must function at all times to keep a plant healthy. Anti-desiccants actually cause leaf temperatures to rise above air temperatures due to the greenhouse effect created by the leaf coverings. If you were to examine microscopically the surface of sprayed leaves within two to three weeks following treatment, you would notice cracking and flaking of the anti-desiccant film. Even so, the chemical still traps in heat and raises leaf temperatures. Higher leaf temperatures means the leaves must increase their metabolic activity to transpire. Working harder in winter stresses the plants.

Anti-desiccants have nothing to do with increasing the cold-hardiness of plants, which is based on genetics. The best way to provide your plants with maximum winter protection is to keep them from drying out. Make certain that the soil is moist just prior to the ground freezing. Moist soil freezes much more slowly than dry soil.

So don’t waste money and time on chemicals: Just using some extra tender loving care will keep plants around until spring.

Ask Dr. Gouin your questions at All questions will appear in Bay Weekly. Please include your name and address.

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