A number of evergreen trees and shrubs suffered serious damage during the winters of 1976-77 and 1977-78 due to abnormally cold weather. Their foliage transpires (gives off moisture) also during the winter months, and when the roots are in frozen soil they cannot replace the moisture that is lost and desication occurs.
There have been many inquiries about the value of anti-transpirants or anti-desiccants in preventing such injury. Anti-transpirants are designed to reduce the loss of water by the foliage by clogging the pores.
"I have come to the conclusion that anti-transpirants are not worth beans in reducing winter injury to ornamentals," says Dr. Francis R. Gouin, University of Maryland ornamental horticulturist.
"If winter injury was due primarily to loss of moisture, it would be possible to grow camellias, southern magnolias and Chinese hollies in upper New York state and in Canada. We could accomplish this by simply spraying them thoroughly with a good anti-transpirant in the fall and possibly once or twice during the winter months.
"But we all know from experience that these species have northern limits. Anti-transpirants can in no way protect plants from minimum winter temperatures and the more we study winter hardiness of plants, the more we begin to appreciate plant hardiness zone maps.
"True, we can often grow plants in colder zones than those recommended by selecting or creating suitable micro-climates. However, when we experience winters like 1976-77 and 1977-78, we discover that micro-climates are also subject to surrounding environmental changes such as abnormally low temperatures and many borderline plants don't make it.
"Last fall I used anti-transpirant (Vapor Gard and Protect 400w) and also water on Japanese privet. Pyracantha coccinea 'Lalandei' and loblolly pine for winter protection. The materials were used according to manufacturer's recommendations. The foliage was thoroughly sprayed over and under until run-off.
"In mid-April and mid-May this spring the plants were evaluated visually. There were absolutely no differences between plants treated with tap water and those treated with either of the anti-transpirants. Neither of the anti-transpirants prevented desiccation of the foliage. The foliage turned brown in midwinter regardless of treatment. By mid-May, most of the brown leaves on the privet and pyracantha had fallen and the new spring growth appeared normal on all plants regardless of treatment. Winter injury was severe with the loblolly pines in both treated and non-treated areas.
"On the positive side, I am convinced that anti-transpirants are a definite asset in summer transplanting of evergreens and deciduous plants. Landscape contractors and nurserymen have seen for themselves the benefits of anti-transpirants when digging large shade trees in midsummer.
"Tree thoroughly sprayed with a good anti-transpirant just prior to digging are slow to wilt. This is a good indication that anti-transpirants do restrict the movement of water vapors out of the foliage. When anti-transpirants are combined with hardening-off or conditioning, such as placing the plants under mist for several days prior to shipping, the survival rate of large shade trees has been increased considerably.
"Many vacationing gardeners have discovered that anti-transpirants can reduce the need for house plant sitters while they are away.
"Watering a house plant well and spraying the foliage thoroughly with a good anti-transpirant eliminates the need of watering for one to two weeks.
"Christmas tree dealers have learned that spraying trees with anti-transpirant just prior to cutting helps maintain freshness in the sales yard much longer.
"Anti-transpirants have also been found effective in reducing salt damage to evergreen plants growing along highways that are salted periodically during the winter months."