From now until February, keep Christmas cactus in a sunny location, with evenly moist soil and low night temperatures (but not freezing). In February, keep it cool, from 50 to 60 degrees, all the time and reduce watering. As days grow longer in March, give it more sunshine and water. In April, you can start the summer schedule of fertilizing every 2 weeks.

Many houseplants are dormant now in response to the colder weather and short days. Water only when they really need it. Soil surface should be dry to the touch before watering. Do not water cacti and succulents unless they begin to shrivel.

Don't succumb to the temptation to feed your indoor plants just because they don't seem to be growing. Winter is a time of rest for many plants. In their semi-dormant state, they need less fertilizer. Most foliage plants can go four months -- November to March -- without feeding. Flowering plants may need feeding every two weeks when in bud and bloom, but even these require smaller amounts between November and February.

If plants are spindly and pale, inadequate light may be the cause rather than a lack of nutrients.

The basic rule for feeding: when in doubt, don't. Fertilizer that the plant does not need and cannot use accumulates in the soil and burns the roots and may kill the plant.

Keep an eye out for insect pests. Pick off scales with fingernails or lift off with tip of nail file. Use a cotton swab dipped in alcohol to remove mealy bugs. Take plants to kitchen sink an wash with mild soap and water solution, and rinse. Cover soil surface with aluminum foil to prevent splashing soil from pot.

Remember that your holiday gift plants will last much longer in bright light and cool -- 60 to 65 degrees -- temperatures.

Impatient gardeners make a big mistake in starting seed too early. If held too long indoors, seedling plants outgrow their pots and become spindly and weak. By all means, order seeds early from the enticing description in the seed catalogs that arrive with the post-Christmas mail, but delay planting indoors until about six weeks before it will be safe to set plants out in the garden.

For Alice R. Freedman and others of Silver Spring who have inquired by letter and telephone, local sources of Wonderlite are: Greensleeves Plant Store, Vienna, Va; Bittersweet Hill Nursery, Rte. 424, Davidsonville, Md; Tropica Stores, in Bethesda, Landover and Crystal City.

Mail orders are accepted by the producer, Public Service Lamp Corp., 410 W. 16th St., New York, N.Y. 10011.

Jory Halston, Washington: A friend gave me a Never-Never plant. Does it have another name? Does it get flowers? How shall I take care of it?

A. The Never-Never plant is Ctenanthe oppenheimiana tricolor. It is related to the Prayer Plant.

Ctenanthes come from the jungle floor of Brazil and they love humidity, filtered sun and moist soil, so be guided accordingly in caring for your plant. A north window or curtained east window, a pebble tray to increase humidity and regular watering will keep it growing well. The average home temperature will suit it.

The Never-Never plant can grow to be three feet tall, but, short or tall, it is a striking addition to the indoor garden, especially in a group of all-green plants. Its long leathery leaves are striped white over green and silver; the wine-red of the undersides glows through the upper surface giving a pinkish cast. The leaves grow in tufts and on my plant are held almost horizontally.

I have not found any reference citing whether Never-Never plant will flower in the house as Prayer Plants do. The botanical description indicates that the flowers are crowed on a spike. The name, Ctenanthe, is derived from Greek words meaning comb and flower.

Carolyn Cole, Alexandria: I am doing a biology project on hydroponic gardening. Could you refer me to a local organization engaged in hydroponic research so I can get the latest developments? I am finding it difficult to locate information on its use.

A. I suggest consulting the reference section or card catalog of your school library or local public library under the hyproponics heading. There are numerous books, both popular and technical, on this subject. Research has been conducted at a number of state agricultural experiment stations but I do not know of an organization with which you could make a personal contact locally.