One of the most serious problems of foliage house plants during late fall and winter is overwatering. In most homes, temperatures are much lower then than they are during summer and early fall.

When temperatures drop to 55 degrees to 60 degrees at night and 60 degrees to 65 degrees during the day, houseplants go into a rest period: they don't grow and use very little water. If they continue to get as much water as they were receiving previously, the soil becomes saturated and there isn't enough oxygen in the soil for the roots to survive.

Many people believe small amounts of water should be applied frequently because they've been told to keep the soil uniformly moist. This is wrong: when the soil is in a constantly moist condition, there usually isn't enough air in the soil for the roots.

Instead, specialists recommend that whenever the soil is dry enough, water should be applied until it comes out the drainage hole at the bottom and not applied again until the soil is dry enough to require it. Room-temperature water should be used, and the saucer should be emptied about 15 or 20 minutes later. Cold water will seriously damage the roots, and if the pot stands in water for long the roots may not be able to get oxygen.

If the pot has no drainage hole, it's hard to tell how much water to apply. In general, a container that holds a quart of soil will probably require half a pint of water to moisten it adequately without causing an accumulation of water at the bottom of the pot.

Small planters or dish gardens rarely have drainage holes, but because the soil is usually rather shallow, they dry relatively quickly. Sometimes the soil can be watered and about five minutes later the container turned on its side on the kitchen sink so that excess water can drain out.

The key to success is letting the soil get dry. With large containers, when the soil is dry at the surface it still may be moist enough in the lower regions. The soil will dry more rapidly in a clay pot than in one that is impervious such as plastic or metal.

The soil in the lower regions will be the last to dry out, and if the soil is not dusty at the top when the water is applied, it may become waterlogged, and the roots severly damaged. Q. I received a beautiful bonsai, a pine for Christmas and have been keeping it on my windowsill facing south. Now I am told it will not survive if kept indoors in a heated room during the winter. Is this true? A. Pine trees, except those that grow in the deep south and in tropical forests, won't survive unless their chill requirement is satisfied during winter months. The gradual shortening of days and lowering of temperatures in the fall cause acclimating or hardening for winter. lBefore they can break dormancy and resume growth in the spring, they must experience several hundred hours of temperatures below about 45 degrees F. That's why your bonsai may not survive if kept in a heated room this winter.

Perhaps you can find a cool place indoors where the plant can get good light during the day and also adjust to the lower temperatures and get its chill requirement. Q. I saw a flower arrangement with poinsettia bracts. Do they need special treatment for use this way? A. Normally they will last 14 days at room temperature after being cut if the green leaves are removed (not the colored bracts). Stems placed in boiling water for 30 seconds will hold up for about five days with the leaves attached. They can be used successfully in foam materials as well as in plain water. Q. I have tomato, cucumber and squash seeds left over from last year. Will they be all right to use this spring?

A. When dried and kept in a glass jar at room temperature, tomato seeds are good for about six years, cucumber seeds for about five years and squash seeds for about four years. They keep longer when they get little moisture from the air. Q. We want to plant several trees in our big back yard, including some that are attractive to birds. Which ones are best for that? A. Snowdrift crabapple is city tolerant and its fruit attracts birds in late October and early November. Redbud crabapple will provide food in late winter and early spring, when birds' food supplies are limited. Flowering dogwood fruit ripens in early autumn, and birds often eat it before it falls to the ground. Winter King hawthorn provides food during February and March.