Mrs. Flavil Boyd, Washington: My ficus benjamina has been in a 17-inch pot for 10 years; it is about eight feet tall. It was moved from Chicago to Washington June 30. It is in a sunny corner - east and south windows, with no draft, no radiators. It has dropped and put on new leaves three successive times. Each try at new growth is less successful. I water it two or three times a month: the soil never dries out. There are white "midgets" walking, milling around under the pot and any leaves that fall into the pot. Help!

A. Ficus benjamina, as an indoor plant, is meticulous in its demands. If these demands are not met, the tree will rapidly drop its foliage - and die.

Ficus benjamina does not like to be moved and often will have trouble adjusting to a new environment. In a good location, it will eventually adjust. There must be good light, preferably through a window with morning sun, or bright, indirect light. There should be no drafts from heat vents or air-conditioning or opening and closing doors. Night temperatures of 65 to 75 degrees and day temperatures of 75 to 85 are ideal. Abrupt raising or lowering of temperatures will cause defoliation.

Leaves will fall from either too much water, or too little. The soil should be allowed to become moderately dry between thourough waterings.

In the case of this particular tree, the owner fails to mention how the plant was transported, whether it has ever been repotted in 10 years, whether, or how the tree is fertilized.

Transportation shock may have been more than the tree could stand. Cold, heat or wind all have adverse effects. Exhaust fumes in a closed truck are often lethal to plants.

This plant may need fresh soil. Removing several inches of soil from the pot and replacing it with fresh potting soil would be beneficial if it has not been repotted in recent years.

A general purpose houseplant fertilizer applied at six-month intervals is recommended. However, do not fertilize an obviously ailing plant.

he white "midgets" descirbed in your letter could be springtails, nuisance pests that sometimes become plentiful in moist situations where there is much organic matter. They chew on tender plant parts, particularly parts near ground level. Spray soil surface, pots and saucers with malathion. Do not spray the plant excessively and never spray in sunlight.

Shirley Krutilla, McLean: My dieffenbachia had quite a growth spurt. It is now about five feet tall with huge leaves and is top-heavy on a tall, thin stem. Can I repot it deeper in the soil, submerging the stem as one would do with tomato plants?

A. This is one of the most often repeated questions. Dieffenbachia, dracaena and aphelandra (zebra plant) are probably the worst offenders in growing tall and leggy, with a bare stem and a cluster of leaves at the top.

You can cut your dieffenbachia down to an acceptable size, rather than trying to grow it deeper in its pot.

Take a sharp knife and cut off the leafy top of the plant. Gauge the amount to be cut off according to the size or height you want in the new plant that will grow from this pruned section.

Dieffenbachia can be rooted in water. Add a pinch of charcoal to keep the water fresh, and change the water frequently. Keep it in bright light until roots form. Then it can be planted in your regular planting mix.

The stub of the plant that is left in the pot should send out new shoots if you give it your customary care of moderate watering and bright light. If the remaining cane is exceedingly tall, chop it down to soil level. Cut this stalk into three-inch segments, lay them horizontally half-submerged in a rooting medium, keep the soil barely moist (or cover with a plastic bag to retain moisture) and in about a month the new growth will begin to emerge.

Irene Zolnaski, Washington: I have tried many variations of watering and sun exposures, but my avocado tree still gets numerous leaves with brown, dry edges. Can you help ?

A. Lack of sufficient humidity is a possible cause of brown leaf edges and tips. The dry air of heated homes dessicates the leaves. Keep the plant out of direct sunlight most of the day and mist the leaves twice a day. Grouping plants helps to concentrate humidity around them benefits all in the group.

Brown leaves also can be caused by too much watering. Moreover, fluoride in tap water is also sometimes the cause of brown edges. Remove the brown leaves and try watering with distilled water for a while. If the new foliage remains green, continue to use distilled water for your avocado.