Mountain laurel, azaleas and rhododendrons may suffer serious injury from prolonged low temperatures during the winter when the soil freezes rather deeply. The roots are unable to absorb moisture from frozen soil, the foilage continues to give off moisture and desiccation occurs.

The plants can be helped considerably by reducing the moisture the plant gives off, or transpires. This can be done by making a windbreak of burlap or plastic attached to 2" x 2" posts around the sides of the plants, and shading the plants from the sun's rays with burlap attached to the tops of posts. A two- or three-inch mulch of woodchips also helps.

There have been inquiries about the value of anti-transpirants or anti-desiccants in preventing injury. Can they reduce the loss of moisture by the leaves?

"I have come to the conclusion that anti-transpirants are not worth beans in reducing winter injury to ornamentals," says Francis R. Gouin, University of Maryland ornamental horticulturist.

"If winter injury were 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," he says.

"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 these plants from minimum winter temperatures, and the more we study winter hardiness of plants, the more we begin to appreciate plant hardiness zone maps."

Bark splitting on young newly planted shade trees can be prevented by wrapping the trunks with treated paper or burlap, or painting the stems and lower branches with cheap white latex paint, according to specialists.

The white paint reflects the light and mnimizes rapid temperature fluctuations.

The best way, in fact the only really good way, to prevent damage from extreme cold is to use plants that won't be damaged by the low temperatures. A lot of gardeners gamble with this, and many lose.

Each plant variety has its own degree of cold hardiness, which depends on its genetic makeup. One variety may be hurt if the temperature goes below freezing while another may be able to survive -20 degree F. when fully hardened (cold-acclimated).

Another kind of winter injury is caused by plants' failure to harden in time for winter weather and their tendency to break dormancy in late winter when mild weather occurs and is followed by freezing weather. Q: Can leeks be grown indoors during the winter? A: It's much better to plant them outdoors in early spring. They continue to increase in size until late fall.They can be left in the ground and harvested fresh during winter and early spring in areas where temperatures do not go much below zero. The edible part of the leek is the steem, which is blanched by covering it with soild to keep it white and tender. Q: We want to plant three or four maples in our yard. Which ones have the best fall color? A: Sugar maple, Norway maple and red maple provide excellent shade and brilliant colors of orange, yellow and red in fall. The silver maple is not recommended: The wood is brittle and when the tree reaches a certain size it can be damaged during wind and ice storms, and the root system often causes problems with sidewalks, drives and septic tanks. Q: I've heard that it harms a peach tree to prune it in midwinter. Is it true? A: A lot of damage can occur to peach trees when pruning cuts are made during November, December, January and early February. This is caused by the sap's freezing and thrawing, the spread of diseases and some reasons still unknown. Wait until early spring -- or even until they are in bloom. Q. Last spring it planted honeydew melon seed. The vines that came up were vigorous and had many blossoms, but when the melons developed the vines shriveled and died. What could have caused it? Most likely it was due to a bacterial wilt disease that's spread by striped cucumber beetles. Weekly sprays with sevin should provide adequate protection. Directions on the label should be followed closely. CHRISTMAS GREENS: The Christmas Greens Exhibition of the National Captial Area Federation of Garden Clubs will be at the Botanic Garden Conservatory, Maryland Avenue and First Street SW, through this Sunday, 9 to 5, open to the public, no charge. Exhibits will provide ideas for Christmas decorating with demonstrations at 11 and 1 each day on how to make holiday decorations.