LAST SUMMER dry weather caused considerable damage to vegetable gardens, trees, shrubs and flowers in many areas. The quantity and quality of the yield from vegetable gardens was much less than it should have been. Many, perhaps a majority, and particularly new gardeners, watered their vegetables but did it improperty applying too little or too much.

Watering too little of too much is happening again this year in some areas, according to a rather extensive survey.

When soil is nearly dry the plant begins to wilt because the roots are unable to replace the moisture that evaporates from the cells (transpiration) and the plant is in trouble.

Sprinkling for 5 or 10 minutes does very little good; as a matter of fact, it may actually have a harmful effect. It could cause plant roots to come to the surface for water There they will suffer even more unless they are constantly watered.

Cabbage and spinach may have root systems 6 to 10 inches deep, beans about 12 inches, sweet corn about 2 feet, and tomatoes and asparagus 3 feet or more. However in gardens with a clay hardpan not far below the surface, tomatoes and other plants have a root system less than 1 foot deep.

Tomatoes and sweet corn need about 1 1/2 inches of water weekly; cauliflower, lettuce, beets, turnips, potatoes and onions do best with about 1 inch of water every week or 10 days; and sweet potatoes, watermelons and pumpkins suffer less from drought than most of the others.

If too much water is applied or drainage is poor, it is likely to prevent oxygen from reaching the roots and the plant is in serious trouble.

Because roots do most of the absorbing, the moisture should be available to them about 6 inches deep. In sandy soil, a half inch of water will soak down to 6 inches; in clay soil it will take from 1 to 1 1/2 inches of water to soak down 6 inches when the soil is dry.

If you use a sprinkler, set out 4 same size cans within the sprinkling areas. Turn on the water for 30 minutes. Pour the water from all the cans into one can. Measure water depth with a ruler. Divide by 4 to get the average. Then adjust your watering time accordingly (if measurement is a quarter inch, run sprinkler for 60 minutes to deliver a half inch).

If the water is applied faster than the soil can absorb it, there will be runoff. To avoid this, reduce the flow of water, and also put a small mound of dirt around each plant to hold the water.

The best time to water is early morning or late afternoon. From mid-morning until mid-afternoon the hot summer sun and drying winds will rob you of part of the water you are applying.

Q. I have a chance to get some municipal sewage sludge. Is it safe to use it in my vegetable garden?

A. It now appears that the heavy metals in some sludge may be hazardous to human health, according to University of Illinois specialists. Gardeners who have applied it to their vegetable gardens in the past but have left it on the surface are advised to mix it thoroughly with the soil to a depth of about 8 inches to help dilute the available cadminum. Gardeners are also advised not to grow leafy green vegetables in areas where sludge has been applied within the previous three years.

Q. When should broccoli be planted for fall harvest?

A. The variety "Premium Crop Hybrid" an All-America winner, matures in 58 days and should be planted at least that long before the average date of the first frost. It will survive moderate frost.

Q. The leaves on two of my dwarf apple trees have been turning black and falling. What is wrong?

A. Apple scab has been rather bad this year. Usually it causes black spots on leaves and fruits, but lately the foilage has completely blackened and some of the fruit is deformed. The fungus overwinters on fallen leaves; when spring comes, spores produced on these leaves land on newly emerging apple leaves. Rake up fallen leaves regularly being sure to destroy them or haul them away.

Q. What materials are best for compsoting?

A. From the house, fruit and vegetable peelings, shredded newspapers, wood ashes, eggshells, coffee grounds and tea bags; From the garden: grass clippings, hedge trimming, shredded leaves, animal manures.

Q. I'm planning to have a vegetable garden next year for the first time. Do you have any ideas on the best location for it?

A. Locate the garden near your home if possible; since vegetables should receive at least 8 hours sunlight each day, do not put it in a shaded spot; have your soil tested at the state university and find out how much lime and fertilizer to use; and select fairly level land.

Q. Why do my squash blossoms fall off?

A. Squash has male and female flowers on the same plant. Male flowers usually fall off because their main function is to pollinate. Female flowers should remain on the plant and produce the fruit. But if the female flower has not been pollinated, it very likely will fall off also.