For the indoor gardener the January lull after a busy holiday season is not necessarily a period of inactivity. There will be the routine day-to-day care of your plants, preserving the beauty of Christmas plants, and contriving time for new ventures in gardening.

Soon the days grow longer and anticipation sprouts along with new buds and leaves on indoor plants, signs of renewed growth in response to increasing length of the days. Give a quarter turn regularly to plants in windowsill gardens so that they won't grow lopsided from reaching toward the light. Don't let leaves touch cold windowpanes.

Long petioles on African violets may be an indication that plants are receiving insufficient light. Move them to a window with brighter light or closer to the fluorescent tubes.

Dust the large-leaved plants such as Ficus elastica, Ficus lyrata and Schefflera. Misting will also help to keep them clean, or you can take them to the shower for a gentle cleansing. Rinse small plants at the kitchen sink in a spray of tepid water. Cover the soil with foil or plastic film to keep it from washing out of the pot.

If you haven't done it before, provide for increased humidity by setting plants on a pebble tray deep enough to maintain an inch of water on the pebbles but not allowing pots to sit in water.

Care for holiday gift plants to keep them attractive as long as possible.

Azaleas - keep moist and cool; mist occasionally; pick off wilted flowers.

Poinsettias - keep evenly moist; place out of drafts but give fresh air and bright light.

Cyclamen - keep temperature no higher than 70 degrees - even lower is preferable; provide good light and humidity; don't get water in crown of plant when watering.

Kalanchoe - give full sun and moderate watering; let soil dry out between waterings.

Christmas pepper and Jerusalem cherry - bright light, plenty of water and cool temperatures. Low humidity will cause leaves to drop. The peppers are edible; the "cherries" are not. Save seeds to start new plants later.

Flowering bulbs - keep them cool; moving them to a cooler location at night will help to keep the flowers fresh.

Plant a pot of oats for the delectation of your cat. Seed germinates in a day or two. Provide good light to green the blades. When plants are 3 or 4 inches tall, present them to your favorite feline as a special reward or as a pick-me-up to survive the winter doldrums. Ask for "Judy's Wild Oats" at Flowers & Plants Etc., 1378 Chain Bridge Rd., McLean, or at your garden center. Too, I have had occasional success growing a tempting crop from leftover lawn grass seed.

In a small aluminum pie plate or tart pan full of vermiculite sprout some cress. It will be ready to use in a week. Snip off the tiny plants with kitchen shears to add a piquant favor to winter salads and sandwiches. You'll find Curly Cress listed in Park's and Burpee's seed catalogs.

Start an avocado tree. Wash the seed and remove the papery brown cover. With pointed end up, insert three toothpicks in the seed so that it will rest on the rim of a glass or jar. Suspend the seed, broad end down, in the jar of water with the bottom sitting in about 1/2 inch of water. Set the jar in a warm place out of direct sunlight. Remember to replenish water lost through evaporation. In a few weeks, roots will appear at the bottom and a leaf sprout at the top. After a number of leaves have grown and there is a mass of roots, plant the seedling in an 8 or 10-inch pot of any good growing mix, leaving half the seed above the surface of the soil. Water thorughly and place in full sun. As it grows taller it may need a stake to keep it upright.

Study the nursery catalogs that arrive in droves immediately after Christmas. Select something new to enliven your indoor garden in 1978.

New this year is White Dot, or Freckle Face, except the spots are white. The Latin name is Hypoestes.

Coleus is easily raised from seed; this year new color variations and fringed leaves are featured in coleus introductions.

Miniature roses avilable in great variety of color will launch your indoor garden toward new rewards of pleasure.

The Cape Primrose (Streptocarpus) and Miniature gloxinias (Sinningia) are increasingly available in garden centers and are recommended as a change of flowering plants for indoor gardens.

Happy new gardening year.