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Last summer our cabbage, broccoli, and cauliflower were infested with green cabbage worms which were so thick in the broccoli that I couldn't even dislodge them when washing the broccoli to eat. I don't want to use toxic chemicals on the plants. What do you say? There is an excellent microbial insecticide called Bacillus thuringiensis, harmless to humans, pets, and all wildlife except the larvae of moths and butterflies which chew on your plants.

It appears to destroy all lepidopterous larvae which ingest it, thus eliminating the larval stages of the cabbage looper, gypsy moth, tomato hornworms, and dozens of other harmful pests All you do is apply the spray to the foliage where the larvae are feeding.

We are hopeful that we can educate the public to demand such pesticides, which do not damage the environment. This insecticide is available under such trade names as Dipel and Thuricide.

We are attempting to grow some plants indoors so that we can set them out later in our garden. They sprouted fine, but now are about 3 inches tall and getting very spindly. They also look pale, even though we have fertilized them. Someone told us that fluorescent lights would take the place of the sunlight which is lacking in our northeast window where we have the plants. We have the lights hanging from our ceiling about 3 feet above the plants. You have the fluorescent lights too far above the plants. Try suspending them on chains or ropes so they can be lowered to about 5 inches above the plants, then raising the lights gradually as the plants grow taller.

Plug-in fixtures with a cord long enough to be adapted to adjustable heights are available.

We have found it helps to have one ''daylight'' and one ''natural'' shade fluorescent tube in each 2-tube fixture. ''Daylight'' tubes furnish more blue and violet rays; ''natural'' tubes furnish excellent orange and red rays. All are necessary to good growth.

These rays will be visible to the eye only as slight tints in the light emitted.

We are fairly new gardeners and have been pleased with the results. However, last year our summer squash started producing well, then just started wilting, one by one. What happened and what should we do? There were mounds of wet sawdustlike stuff near the base of the plants. The ''frass'' you speak about at the base of the plants indicates you had squash vine borers. A wasplike moth lays eggs at the base; in 6 to 15 days they hatch and enter stems.

In cooler areas of the country they lay eggs in late June; in warmer areas late April or May. Adult larvae enter the soil to overwinter, hence one precaution is to gather and destroy the vines right after harvest. But this season you can keep an eye out for reddish eggs and destroy them.

If you see the frass, slit the stems lengthwise and stab or remove the borers with a knife or wire. Mound moist soil over the wounds and the vines will reroot. However, dusting the vines just as they start to run will usually kill the larvae as they hatch.

Keep dusted with Rotenone (especially after rain) for about a month. Rotenone is accepted by both organic and chemical gardeners.