Many apple and peach trees and grape vines have a tendency to bear too much fruit. The tree or vine can nourish and properly ripen only a certain quantity, and too big a crop results in delayed ripening and low quality fruit.

To prevent too much fruit, thinning (removing some of the fruit) is a standard practice among commercial fruit growers. It not only results in increased size of the remaining fruit by also improves color and flavor.

Most peaches should be thinned soon after the so-called June crop. This usually occurs a month to six weeks after bloom. It's generally recommended that the peaches should be spaced six to eight inches apart.

A large mature apple tree can produce between 50,000 and 100,000 blossoms, most of them attached to spurs. If all 50,000 or more blossoms were to set fruit, the tree would produce as many as 800 bushels of apples, each one quite small.

Even the fruiting of 20 percent of the blossoms would be prohibitive, resulting in no blossoming the following year while the tree replenished its reserves.

It takes about 30 leaves to furnish one apple with the carbohydrates it needs to mature. Within five or six weeks after full bloom, the apples lagging behind in nutrition die and fall from the tree in what is called the June drop.

Thinning should take place soon after the June drop. You'll have to guess how much to remove, but if the tree is in poor health, plan to leave only enough for each apple to have about 40 leaves to provide its nourishment.

Weather conditions and insects also can reduce the apple crop -- hail storms strong winds that whip the apples into the branches, causing scratches and bruises.

During the last month on the tree the apple develops its characteristic coloration. When picked, it's sweet because of the sugars it has converted from starch. Its tartness comes from the acids, especially malic acid, involved in respiration metabolism.

One effect of too big a crop of grapes is that the fruit is not as large, sweet and tasty as it could be. Another effect is poor bud formation for the following year.

Grapes are different from most fruits in that they do not mature and improve in quality after harvest. They must develop all of their sugar and fine flavor while still on the vine. The best way to determine when they are fully ripe is to pick a few and taste them. Q: What is the secret of growing eggplant? I've been trying for years without success. A: Eggplant is a close relative of the tomato and thrives under similar conditions. They need full sun; don't plant them near trees, tall shrubs or on the shady side of tall growing crops. They bear throughout summer and fall, so don't plant them where they interfere with late-planted crops. Plant them three feet apart in the row, and give each one at leat 12 to 25 square feet of space. Q: I have a silver maple in my back yard about 60 feet from the sewer system. Will its roots spread to the sewer system? A: Its roots do spread and can clog sewers and lift pavements. Only time will tell whether your tree is far enough away not to cause damage. Q: We have mushrooms growing in our lawn. They look like those sold at the store.Can they be eaten? A: Many poisonous kinds grow side by side with edible ones, and there's no simple test to distinguish one from another. By far the best policy is not to eat them. Q: Last fall we removed a limb from our dogwood tree. This spring the sap keeps dripping from the wound. We applied a dressing, but it did not stop the sap. Can you suggest something that will help? A: Application of a wound dressing will not help -- in fact, it will not adhere if applied when the wood is wet. The bleeding does little harm -- it's mostly water -- and will stop when the tree is well covered with foilage. Q: I've just received some literature about the organic way of gardening. It says commercial fetilizer should not be used. What's the scientific point of view about this? A: Robert L. Carlus, Michigan State University professor of nutrition, wrote: "If the soil is low in nitrogen or nitrogen is not applied, crops grown the 'organic' way are spindly and stunted, yields are low -- and both the people and their livestock are emaciated due to low productivity."

"Q: Do you recommend watering the vegetable garden at night to keep the sun from scalding the leaves? A: Watering vegetables during the day does not harm the leaves, but watering in late afternoon or at night will promote development of some diseases. The best time to water is early morning. Late afternoon is all right also, if the leaves have time to dry before dark. Q: Will burying the runner from our grapevine produce a new vine? A: Yes, simply cover a portion of new shoot with soil, leaving the growing tip exposed. Roots will form on the covered portion. Cut the rooted portion off next spring and transplant it. Q: My geraniums growing outdoors bloom fine, but they get occasional yellow leaves on them. Is there a way to stop it? A: Yellow leaves on geraniums usually indicate root injury due to over-watering, poor drainage or under-watering. Leaves discolored and smaller than normal may indicate a need for fertilizer as well as a moisture irregularity. Most varieties do best in full sun, although many bloom well and perhaps have more attractive foliage with sunlight during the morning and light shade in the afternoon. Q: What causes leaves on a birch tree to become wrinkled and discolored? A: Usually it is caused by aphids (plant lice) feeding on the leaf tissue. They may be seen on the underside of the leaves by opening the leaf so the wrinkled area lies flat. They can be sprayed with mathion to get rid of them. w Q: Are the Irish potatoes you buy in the grocery store suitable for planting? A: Generally not. Many of the potatoes sold in the grocery store have been treated with a sprout inhibitor. It is best to buy certified seed potatoes. Q: When is a good time to fertilize my strawberries?" A: After they finish fruiting in the spring apply four pounds of 8-8-8 fetilizer per 100 feet of row. Scatter the fertilizer over the tops of the plants and brush it off with a broom. Q: Is it true that cold weather last winter means fewer insects in our garden this summer? A: Very unlikely. Some insects, such as blueberry maggots, codling moths and bedbugs, need an amount of quite cold weather to emerge from the larva stage. Otherwise, they would have to wait for years until they get cold enough. Q: I have two apple trees that attract many bees. How can I keep them sprayed without harming the bees? A: Apple trees should not be sprayed with an insecticide while they are in bloom. When the flowers are gone, the bees no longer visit them and spraying can be done without harm to them. Q: My old rose bushes are having some yellow leaves. The yellow leaves do not have black spots, and the bushes look healthy and bloom nicely. What do you think could be wrong? A: Spider mites could be responsible; they are particularly bad during hot, dry weather. Use a magnifying glass and take a look at the undersides of the leaves. Or hold a sheet of white paper under the leaves and thump the branch hard. If mites are present they should fall on the leaves. Spraying the plants regularly with water from the garden hose should provide fair control. Q: If I put mothballs around the shrubs in front of the house, will it keep dogs and cats away from them? A: Mothballs have questionable value as a repellant for dogs and cats. The mothballs are poisonous and should not be put anyplace where children may get at them.