Christmas gift ideas for the indoor gardener are varied and plentiful. Garden centers, florists and other shops offer a wide choice of usual and unusual items.

Hardware, tools and appliances can be bought early and hidden until the gift-giving day arrives. If you are buying plants, it is wise to place your order with a florist or plant store early for delivery or pick-up on or near a specific date.

When buying plants, for the indoor gardener who has a special plant hobby or for a young person newly enthusiastic about plants, consider a specimen plant and a membership in a plant society.

Here are a few ideas:

Begonia 'Tiger Kitten' and membership in the American Begonia Society.

A paphiopedilum or phalanopsis orchid (which are beginner's species); inquire at Kensington Orchids, 933-0036, about plants and membership in the orchid society.

Miniature Sinningia 'Dollbaby' or Streptocarpus 'Constant Nymph' and membership in the indoor light gardening society.

A bonsai or a plant in training for bonsai.

All the societies listed have local chapters. Names and telephone numbers for local contacts for these and other plant societies can be obtained from the American Horticultural Society, 768-5700. The American Horticultural Society is the national organization of gardeners - professional and amateur, indoor and outdoor. Membership is open to all and includes several publications as well as a variety of activities and services for members.

Membership in a plant society is a gift that keeps giving all year long.

Some other suggestions may help you in your shopping expeditions.

The indoor light gardener will welcome a thermometer and humidiguide to monitor temperature and humidity, a timer for lights, a light meter, a gift order for fluorescent tubes or other equipment.

For the gardener who likes to display plants artistically throughout the house or on the patio, choose a fine example of local pottery. Many plant shops now handle signed products of local artists.

Aids for work-a-day chores are always needed. Small tools, pot labels and stakes, a plastic spray bottle for misting (old ones tend to drip after long use). From House in Bloom is a new 'all-in-one indoor gardening aid' called Plantool. Made of 20-gauge tool steel and rustproof, it scoops, rakes, prunes, cuts.

With little effort and no expenditure except your time, recycle some plastic and aluminum containers. Indoor gardeners are always inventive in using leftover containers for propagating, repotting, mixing soil or some spur-of-the-moment emergency.

An amaryllis bulb in its own container, already in bloom or ready to start growing, will delight a shut-in, as will a dish of paper white narcissus or planted crocus pot.

And of course, books, books, books! The gardener's pursuit of knowledge about plant origins, culture and legends is spurred by a continuing flow of new books, temptingly displayed at book stores.

Make it a merry Christmas for indoor gardening!

Ferns in Winter

Winter is a stressful time for ferns indoors. Special attention to their care will keep them fresh and green. Probably most important to their health is the relationship between temperature and humidity.

The air in a house or apartment is often hot and excessively dry. As temperature increases, relative humidity decreases. The resulting dryness is injurious to most ferns. You can increase humidity around plants by setting pots on a tray of pebbles which are kept moist or a tray of damp sand. Misting, with caution, will increase humidity, but remember that fungus growth is accelerated by over-moist conditions - a special risk for ferns with finely dissected fronds on which droplets of water are likely to collect.

Temperature requirements depend somewhat on the origin of the species. Most warm climate ferns grow well in the average winter warmth of the home. You should learn to know the preference of the species you have.

If it is difficult to maintain a high humidity-temperature relationship during the winter, keep your ferns in a cool room - 65 to 75 degrees. Avoid cold drafts from windows or doors and hot air from heating ducts.

Size and type of pot and humidity of a room influence the amount of water used by the plant. Some ferns require more water than others. No hard and fast rule can be given for watering.