The yeild from many city and suburban gardens is disappointing because of the soil condition. Soils without organic matter and nutrients will not grow good crops. Each summer and fall gardeners rake up and get rid of tons of fallen tree leaves, old sod, lawn clippings and other plant material, when these materials could be composted and used to improve their soils.

Compost also makes a desirable mulch for use around ornamental shrubs and other plants. Mixed withthe soil, it restores bacterial life, improves its water-holding capacity, provides mineral nutirents and eliminates compaction which keeps roots from respiring properly.

There's a step-by-step system for turning the material into a valuable natural resource.

When building a compost pile, remember that a pile too small will lose heat rapidly and dry out too quickly. Studies have shown that a compost pile of less than 3' x 3' x 3' is too small. It should not be more than 6 feet high when finished. It can be enclosed with chicken-wire fencing or slat fencing to conceal it and protect it from the wind.

Decay of the materials is brought about by microbes which need the right temperatures, adequate oxygen and not too much moisture. If the soil stays soggy, air is excluded, decomposition slows down and offensive odors may occur.

Decomposition of the material is similar to the burning of fuel. In both cases heat is released. The heat inside a compost pile may rise to 150 or even 175 degrees for several days. Most plant disease germs, weed seeds and insect and worm larvae are killed, usually within 30 minutes, by a temperature of 140 degrees.

Shredding speeds composting. Most materials can be shredded by running over them several times with a rotary mower. Shredding increases their surface area and their susceptibility to microbial invasion.

To build the pile, put a layer of leaves two feet deep on the ground inside the enclosure. Mix other materials with the leaves if they are avialable. A small amount of good surface soil mixed with the leaves will speed decay.

Sprinkle 5-10-5 fertilizer over the layer of leaves. Wet thoroughly. On top of the leaves put a 2 inch layer of soil. Add two more layers, each two feet deep, and fertilize and moisten each one. Q: How can you tell when Irish potatoes are ready to dig? A: Potato tops usually turn brown when the tubers reach maximum size. However, the tubers are large enough to eat before the tops die back. Try a few. When they're large enough to satisfy you, they're ready. Well-matured potatoes usually are of better quality than immature ones, and they keep much better in storage. Q: The other day a branch from our large oak tree blew down and turned out to be infested with borers. We are worried about the rest of the tree. What can we do? A: One possibility is the branch was badly damaged by wind or whatever before it became infested with borers. Borers seldom attack trees with a good sap flow because it could destroy them. Two or three years of low rainfall are likely to make a tree more vulnerable to borer attack if it's not watered. Improper pruning, wounds caused by lawn mowers and wind damage, all provide sites for adult female borers to deposit eggs. The best way to prevent borers is to maintain plant vigor. Q: My geraniums bloom well but have a lot of discolored leaves. What causes them? A: They usually indicate root injury due to over-watering, under-watering or poor drainage. Leaves discolored and smaller than normal indicate a need for fertilizer as well as a water problem. Most varieties do best in full sun, however, many bloom well and perhaps have more attractive foilage with sunlight during the morning and light shade in the afternoon. Q: The roots of a large oak near the house are pushing up the bricks of a 20-year old walk that passes near it. Is it safe to cut back the roots under the walk? A: It may or may not be safe; it depends on how much the tree needs those roots to keep it from toppling over and to give it moisture and nutrients. Any tree surgeon or experts can make an examination and give you an opinion. The health of a tree is in direct proportion to the extent and effectiveness of its feeder roots. The damage might not kill the tree, but it might so debilitate it that it would become an easy prey to insect and diseases. It takes a long, long time to replace a big oak tree. Q: The leaves of my rhododendron are turning yellow. Could this be due to an iron deficiency? I transplanted it two years ago from a shady spot to one that gets full sun. A: The yellow leaves do not necessarily indicate an iron deficiency. To make sure, have your soil tested. If a rhododendron is planted even an inch too deep, it could be in serious trouble. Even if planted all right, the plant could have settled due to decay of organic matter in the soil mix. Q: I have a dozen Colorado spruce on my lawn, about 25 years old. They're losing their bottom limbs and many needles are brown. Could it be due to air pollution? A: The Colorado blue spruce has a life expectancy of a hundred years or more under normal conditions. After 20 years the lower branches may die and after 35 to 50 years the top of the tree may become thin. As they get older, therefore, Colorado spruce may lose most of the values for which they were planted. Drought, inadequate fertilization, too much shade, air pollution and spruce spider mites can cause these trees to become old before their time. Q: What is the white powdery substance on the leaves of my zinnias, and what should I do about it? A: It probably is powdery mildew, a fungus disease to which some varieties are very susceptible while others have some resistance. The disease can be prevented by spraying every 10 to 14 days with Benlate or Karathane. However, spraying this late in the season probably is not worth while. Q: What is meant by gibbing camellias? One of my friends told me she is gibbling hers. A: Gibberellic acid, available at many large garden centers, is applied to the vegetative bud located next to the flower bud to cause the bloom to mature earlier in the season. Some blooms may appear within 40 to 55 days after treatment. The idea is to have flowers mature before they are damaged by cold weather. Q: What causes my spruce tree to become brown inside while the outside needles are green and healthy looking? A: The dead zone is due to inadequate light, and usually is the result of shearing with hedge shears. At this point if pruning permits better light to reach the interior it does no good, because most of the dead zone is unable to respond. Q: Almost overnight the blooms of my bed of petunias and geraniums started to rot. Why? A: Warm rainy weather can cause development of several fungus disease. The Fungus Botrytis can rot blooms overnight. The disease is much less severe with plants in full sun and not crowded and if dead flowers and leaves are removed daily. Q: My neighbors catch their grass clippings in a bag and remove them. I have been letting mine stay on.Is all right to do so? A: When left on the lawn, grass clippings provide substantial quantities of fertilizer as they decay. However, removal of the clippings is believed to reduce chances of bluegrass becoming diseased. Q: I want to grow cherry tomatoes indoors this winter in clay pots.Will ordinary garden soil be satisfactory? A: It's better to use a special soil mix. Plants absorb most of their water needs from the soil. The small volume and shallow depth of the pot results in a soil water reservoir too small to maintain growth for more than a very short period. At the same time the soil is often too wet and aeration too poor for the plant to absorb even this inadequate supply of water. Potting soil sold at most large garden centers should take care of these problems. The pot should be at least a six-inch one. Q: How can I prevent Irish potatoes from sprouting when I store them for the winter? A: Put your potatoes in a dark place. Try to keep the humidity at 90 to 95 percent and the temperature between 45 and 48 degrees. Potatoes stored at at temperature of 38 to 40 degrees will last even longer without sprouting.