On a hot, dry day a shade tree in the proper place does a better job of reducing the temperatures than a tent or umbrella would do. A single healthy city tree may carry the workload of five average-size room air-conditioners running about 20 hours per day, according to Forest Service research.

One of the best things that can be done to keep the tree healthy is to fertilize every year and water it during prolonged dry weather. It helps the tree to cope with air pollution, diseases and insects.

Young trees should grow faster, middle-aged trees look better and old trees may live considerably longer.

One of the best times to fertilize the tree is in November after the leaves have fallen. The fertilizer should be applied when grass blades are dry. After the fertilizer has been distributed, it should be washed off the grass blades immediately using a lawn sprinkler or a spray nozzle on a hose; if it stays on the blades, and the grass gets wet from rain or dew, it can burn the grass.

Nitrogen is the nutrient most often lacking in the soil and the first to limit plant growth. Nitrogen fertilizers can be safely added to the soil annually at the rate of six pounds of actual nitrogen per 1,000 square feet. Sixty pounds of 10-6-4 would provide the necessary 6 pounds of nitrogen.

The fertilizer can be applied to the soil surface with a spreader under the spread of the branches, keeping at least a foot away from the trunk of the tree. Measure the area to fertilized to find out how much to apply.

The numbers 10-6-4 tell what the fertilizer is: 10 percent nitrogen, 6 percent phosphorus and 4 percent potash.

Nitrogen is the nutrient that regulates the amount of new growth a tree makes. A tree with a limited nitrogen intake usually has smaller leaves than one that gets more nitrogen, and its leaf color tends to be light green. The color turns to yellowish green as the deficiency becomes more acute.

A tree with a liberal supply of nitrogen usually has a dark green foliage color. If the nitrogen is available to the roots before growth starts in the spring, it may stimulate the leaves to grow larger.

On the other hand, if leaf growth has advanced to a considerable degree, the available nitrogen may simply stimulate the tree to grow for a longer period of time.

The leaves of the tree produce its food by the process of photosynthesis. Chemical fertilizers simply represent some of the raw materials needed. The food provides the energy required by the tree to carry on its life functions. Q: I've been told to mulch my strawberry patch. What is the reason for doing it? A: Alternate freezing and thawing may have the strawberry plants out of the soil. Mulching will prevent it. In late fall when plants are fully dormant and the soil is cold, apply a three-inch mulch of pine needles or straw and leave it on until the plants begin to yellow in the spring. It will also conserve moisture. Most of the berry roots are in the upper 10 inches of soil, and dry weather at harvest time can reduce yields 50 percent or more. Q: I have some great big pumpkins and would like to save the seeds. Is it possible? A: yes, but it isn't a good idea: Chances are they will not come true if planted. Q: I've tried several times to grow parsley from seed, and the seeds never come up. How do you make them sprout? a: Parsley seeds are slow to germinate, so be patient with them. Plant the seeds indoors in Jiffy-7s (available at garden centers), keep the soil moist, and when they sprout, plant the pot and all outdoors, after the weather gets warm enough. Seeds barely covered should germinate in about 10 days. Q: Wild mushrooms are my favorite food. Can you tell me of a good book that describes and illustrates them? A: Mushrooms of North America, by Orson K. Miller Jr., published by E.P. Dutton & Co., 359 printed pages, a comprehensive guide to finding and collecting edible mushrooms, 422 species described, 292 photos in full color. Your bookstore can order it for you; it costs $19.95. Q: There is a deep round hole in the trunk of my dogwood tree about the size of a 50-cent piece. Is it due to borers? A: Almost certainly it is due to decay caused by poor pruning. When a branch is removed and a stub of one or two inches is left, healing is very slow and decay-causing organisms have time to become established. As decay progresses, the dead stub falls out, leaving the hole. The best thing you can do for the tree now is water it regularly during prolonged dry weather and fertilize it once a year in late fall or early spring. Q: We planted six rose bushes last spring and they did beautifully. What do we need to do to help them get through the winter? A: Roses need very little winter protection except in the north, where temperatures go well below zero for long periods of time. The best that can be done for the roses is to mulch them to prevent the soil from freezing too deep. Q: I'm enclosing two leaves from my viburnum plant. Would you believe they came from the same plant? A: A plant can have two kinds of leaves: sun leaves and shade leaves. Plant growers became aware of this when they started moving larger trees indoors. Sun or high-light leaves are found on the exterior and top of the plant, and they can't function well unless they get sunlight. Leaves that are in the shade of other leaves have a different internal structure, and if exposed to continous sunlight they cannot function. Q: We planted cauliflower in the spring. It grew fine but the heads never amounted to anything. Can you offer any suggestions? A: The curds or heads of cauliflower are made of tight flower-bud clusters, and when hot weather sets in they just go to seed, failing to develop a usable head. The curds also can be damaged by frost. Q: We have a lot of snap-bean seeds left over. Can we save them to use next spring? A: The seeds can be stored and used next spring. The best place to keep them is in a fruit jar with a screw-top lid, which keeps moisture out. When seeds are well dried and sealed in glass they should remain viable for several years. Q: I have a Chinese evergreen (aglaonema) and Dracaena (corn plant) that need to be repotted. When is the best time, and what kind of potting soil should I use? A: The best time to repot these foliage plants is just before the growing season, so that new root growth will soon penetrate the fresh soil. Usually that's in the spring. These plants make little or no growth during the winter months. For those that need repotting, if the plant has been in a 5" pot, change it to a 6" pot. The potting soil sold at most garden centers is adequate. Q: When our Concord grapes started to turn purple the birds started taking them, so we picked them and took them indoors. Now they have little taste. Why? A: Grapes have to ripen on the vine to have sweet flavor. Once picked, they will not get any sweeter. Q: I collect pine cones year after year for decoration and year after year they last only a very short time. What is the secret of taking care of them? A: The cones should be in good condition when you collect them. Collect mature cones while they are green or light brown and let them ripen or dry out in full sunshine. They will also open fully if placed in a warm oven for several minutes. They can then be preserved by spray painting them with clear shellac lacquer or clear varnish. Q: We are going to plant two red maples in late November. Should we mulch them immediately or wait until the soil gets cold? A: Mulching immmediately will keep the soil in the root zone warm much longer and permit a lot of new root growth before freezing weather. It will also conserve moisture and prevent the soil surface from crusting, which makes water percolation into the soil more difficult. Q: How do you prune Bourbon roses? I planted one a year ago and now it has five seven-foot canes. A: The Bourbons, such as the silvery pink Zephirine with its heavenly fragrance, should be pruned as little as possible. Remove dead wood and the less desirable of two canes that shade each other. Each healthy cane should receive as much sunlight as possible. Q: Are castor bean plants effective in keeping moles away? A: Moles feed almost entirely on grubs and small insects. The best available control for moles is the spear-type mole trap, which can be purchased at many hardware stores. Follow the instructions for use that come with the trap. Also try to get rid of the grubs in the soil. If you do the moles will go elsewhere to feed.