GARDENING : TIME IS RIPE FOR PRUNING IN THE NEW YEAR.

Byline: Joshua Siskin

In Los Angeles, January and February are the months for pruning most trees, shrubs, vines and roses. If you are not really the gardening type (and even if you are), you might wonder why pruning should be done at this moment and, more to the point, why pruning should be done at all.

Let's first address the question of why prune at all. Pruning allows light into the center of a plant. This means that there is more photosynthesis throughout the plant, from the interior branches to the canopy tips. More light means the production of more sugar in every area of the plant. Sugar is the only real plant food, after all; it provides plants with the energy necessary for growth. As a result of pruning, with sugar coursing through more sun-exposed, leaf-covered limbs, a plant is naturally healthier.

Another factor critical to plant health, but frequently overlooked in pruning discussions, is that of air circulation. Where the interior growth of a plant becomes too dense, sucking insects such as mealy bugs, scales, aphids, white flies and thrips take up residence. Thus, regular thinning out to reduce dense interior growth is essential.

There is also the question of hormones. Cutting the terminal or apical bud on any shoot means removing the source of hormones that inhibit lateral branching and ultimately more shoot tips, means more blooms in the spring - especially on roses and other terminal flowering species - than if the plants were left alone.

On deciduous fruit trees - plums, apricots, peaches and apples - pruning is necessary in order to produce fruit of decent size and quantity. When these trees go unpruned, they may produce an enormous number of small fruit - many of which will fall before ripening - one year and very few fruit the next.

Overall, the pruning process is one of invigoration. Deciduous fruit trees and roses, which use up an enormous amount of resources in a single growing season, require regular invigoration if they are to consistently live up to our high expectations for abundant crops of fruit and flowers.

As to the proper time of year to prune, I defer to the wisdom of Dr. Curtis Smith, one of the true horticultural luminaries of our time, who writes for the cooperative extension service of New Mexico State University. The first plants in the garden to be pruned should be deciduous fruit trees, followed by roses and then evergreens. The reason for this has to do with the depth of dormancy reached by these different plants. Deciduous trees, once they have lost their leaves, are completely dormant, and may be pruned at any time from leaflessness ``until their buds begin swelling in the spring.''

On the other hand, writes Smith, ``roses, especially hybrid teas, floribundas and others commonly planted, do not go dormant like deciduous trees; they are merely quiescent, waiting for appropriate weather conditions for growth. Because of their lack of dormancy and the fact that pruning can stimulate growth, caution is advised with regard to pruning dates. If a period of warm weather follows pruning, the rose may resume growth only to be severely damaged by cold weather that follows. Pruning two weeks to a month before the expected last killing frost in the spring helps avoid this problem.'' In Los Angeles, frost is generally not a problem after March 1, which would make late January or even February pruning appropriate.

Evergreens - from pine trees to azaleas - do not experience winter dormancy. Thus, they should be pruned just when the weather warms in early spring.

More tips for pruning roses come from George Howser and Tom Bonfigli, as reported in the Santa Rosa Press Democrat: ``Make final pruning cuts at 45-degree angles, -1/4 inch above dormant bud eyes; the 45-degree cut is important because excess natural sap will rise to seal the cut, pour down the cane and not interfere with the developing bud eye. The cut should be made so the new growth points away from the center of the bush. If a cane is more than 2 years old, remove it. You can tell an old cane by the gray or grayish-white color of the thorns. If the thorns are dark or another color, it may be best to leave that cane on for another year. Remove any blackened stubs or dead branches.''

Tip of the week: According to Sally Joy, of the American Rose Society, don't panic if you accidentally cut off a good rose stem while pruning. Put the cut steam in the ground and it should root. ``I get almost 100 percent take on cuttings during this time of the year,'' she said.