Limited interior space, combined with reduced light and humidity, make it difficult to sustain many plants indoors during the winter. Fortunately, many tropical forest natives and a few common garden plants can thrive in an indoor winter environment to provide greenery and a few bright flowers through the winter.
Because flowering plants need so much light to flourish, very few make reliable winter-long bloomers. The African violet has a centuries-long history as a potted plant that blooms through the darkest winters. This plant tops the University of Missouri's list of flowering houseplants. Amateurs need not be intimidated; the nearly 15,000 varieties are so similar that one set of cultural practices fits all, according to the African Violet Society of America. African violets do better inside--where temperatures are constantly near 72 degrees F and the moisture level is consistent--than they grow outdoors anywhere but their native tropical mountains. A bright window with indirect sunlight or 600 foot-candles of combined florescent and incandescent light will encourage continual blooms through the winter.
Foliage plants that are natives of the forest floor where sunlight is scarce make good guests in winter pots. The peace lily, or spathiphyllum, is one of the plants studied by NASA that might be used to fight indoor pollution because it absorbs volatile organic chemicals (VOCs). VOCs like benzene and formaldehyde tend to build up in tightly sealed modern buildings. Spathiphylla come in several sizes and tolerates low light even better than most indoor tropical plants. With a little light and a monthly dose of half-strength fertilizer, they begin sending up white "spaths"--their version of a flower. Let them spend summers in complete shade outdoors to develop a dark green tan.
Many of the plants grown as annuals in a garden are actually tender perennials. The University of Vermont Extension recommends taking cuttings of many varieties including impatiens, begonias, geraniums and coleus as starts for next year's garden. Alice B. Russell, a North Carolina Extension Specialist, recommends scented geraniums and Martha Washington geraniums (Pelargonium graveolens and P. x domesticum) as good indoor varieties. If kept near a sunny window or provided extra light, both geraniums will bloom through winter and provide cuttings in late winter for more summer plants. Repot compact plants in fresh, clean soil and check for pests; a good shower with water or insecticidal soap should clear up most problems. The scented Pelargonium species, called "citrosa" or "mosquito plant," will also grow well in a sunny window if cut back whenever it becomes leggy and, like P. graveolens, will provide a summery scent for winter days.