FOLIAGE HOUSE plants (those that rarely if ever bloom) are popular Christmas gifts, partially because of their adaptability. They can adjust to environmental conditions better than most other plants and can last a long time with basic care.

Three factors are vital: light, water and temperatures. Humidity is desirable but not essential.

The importance of adequate light cannot be overemphasized, according to Dr. Charles A. Conover, director, University of Florida Agriculture Research Center, Apopka, who is the author of more than 100 research reports on growing foliage and flowering plants.

Without ample light, the plant cannot produce sufficient food for good growth. The plant must utilize stored food and deterioration of plant quality occurs until reserves are exhausted and death occurs.

Light intensity controls to a considerable degree the rate of food production; generally, the more light, the more food production. (Many foliage plants, however, are native to tropical rain forests and are injured when placed in full sun.) Desired light levels are obtained near windows with other than a northern exposure.

When natural light levels are not adequate for foliage plants, they should be supplemented with artificial light sources, such as flourescent lighting, Conover says.

Light duration is also important, since the total amount of light received is a product of intensity and duration. The longer a plant is lighted, the more food is produced.

Foliage plants can grow indoors within a fairly wide range of temperatures. The most desirable temperature range is 70 to 75 during the day and 65 to 70 at night. In general, plants require a lower night temperature than day temperature, although this does not appear to be critical for foliage plants.

Watering generally causes the most confusion but is relatively simple, Conover says. Foliage plants are adapted to regions where soil is moist but not continually saturated with water. Never allow the soil to become completely dry between waterings, and when watering, apply enough water to thoroughly wet the entire soil ball.

If the pot has drainage holes, water the plant until water comes out at the bottom. Wait about 20 minutes for excess water to drain and empty the saucer.

Containers without drainage holes should have a layer of coarse gravel in the bottom to allow a space for excess water. A good way to check these containers for excess water is to lay them on their side in a sink or use a dip-stick inside a hollow pipe.

When foliage plants are used for interior design purposes, little fertilization is required, since it is desirable to keep the plants from growing excessively. A lot of new growth is not wanted since the plants may soon out-grow their location. In mosat cases, four applications of fertilizer a year will be sufficient unless considerable new growth is desired.

Foliage plants grow best with high humidity. However, proper care in watering, temperature control and adequate light levels will do much to overcome the adverse effects of low humidity.

Dust that accumulates on the foliage can be removed by syringing or wiping the leaves with a soft moist cloth. Don't fold, crease or rub leaves too hard, as they may be damaged.