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Q. We think we made a mistake by planting garlic in early May when we put in onion sets. A neighbor said he had heard that garlic should be planted in the fall. The tops are still green and the bulbs are not filled out.

A. Although garlic can be planted in either spring or fall, our garlic-growing friends (commercial growers) plant in late September or early October. They begin to harvest in early August as soon as the tops turn brown.

A good rich, mellow, sandy loam is best for garlic growing. We've tried planting them in the spring, but the bulbs are always small. Fortunately, our friends always give us some of theirs. They have no problems with it coming through the winter, whether it's a mild one or temperatures drop well below zero.

Q. We planted a Japanese tree lilac five years ago and it is supposed to bear large, white, fragrant panicles of flowers. The nurseryman said it was a 2 -year-old tree when we bought it. Why have we had no blooms?

A. We also have a Japanese tree lilac (Syringa reticulata) about the same age and do not expect it to bloom until it is 8 or 10 years old.

The penalty for buying smaller, younger specimens is usually a longer wait for blooms. However, these trees should be used more, since they are attractive and not difficult to grow. They tend to form either a large bush or a small tree.

The trees are slow growers and reach a height of only 17 to 20 feet in 20 years and stop growing upward at about 25 years. They are extremely hardy in most parts of the country, and their tolerance to cold extends to southern Canada (excluding the high altitudes of mountainous areas).

Q. Would you help settle an argument? Do fireflies eat leaves of flowers and vegetables? We have seen them on our zinnias, and these plants are getting holes in the leaves. Also, what causes these insects to glow? We notice some of them are almost wingless.

A. Fireflies are not considered pests of any crops. On the contrary, larvae and some other stages of lightning bugs eat snails, slugs, earthworms, and larvae of other insects. The larvae also produce a glow light. Males are the ones that fly; the females are almost wingless. The flashing is to attract the opposite sex. The light is practically heatless, and the possibility of man's duplicating it has intrigued scientists for years. It is caused by the oxidation of luciferin, in the presence of an enzyme called luciferase.