Indoor gardens are a legacy of the Victorians, who brought back tropical exotics from adventures and built large conservatories to shelter them from the North Atlantic climate. The reliability of today's central heating makes caring for tropicals and other houseplants easy if you create the proper indoor habitats to help them thrive.
Most tropical plants need more light than they can get in the average home, especially during winter when the sun dips farther south. Most native habitats provide filtered light, meaning that setting them in a hot southern window will broil them. Texas A and M University's Horticulture department recommends mixing fluorescent and incandescent lights to provide light at both ends of the spectrum for no more than 16 hours a day for optimum light. By all means take houseplants outside during the summer, but keep them in dappled shade so they won't become accustomed to higher light levels.
Most plants like moist soil, but few like to sit with their feet in water. Poinsettias prefer to let soil dry between watering, but cyclamens begin to go dormant if soil gets too dry. Find out what your plants prefer. "Sprinkling" from the top doesn't wet soil uniformly; it leaves salts on the soil surface and encourages surface mold near plant stalks. Water houseplants by plunging them into a sink full of tepid water, then set them in another sink to drain completely before returning them to their saucers or containers. Properly hydrated, friable soil should drain water within a few seconds. Always aerate city water or let it sit overnight to vent treatment chemicals such as chlorine before using it on houseplants.
Indoor atmospheres tend to lock in pollutants and organisms, making indoor plants more likely victims of molds, diseases and pests. One source for these scourges is the soil in which they live. Houseplant soil should be light, moisture-retentive--and sterile. Purdue's "Ag" extension suggests baking soil in a 180-degree oven for 20 to 30 minutes, and cleaning tools in a ten-to-one solution of water and bleach. Before bringing plants indoors from "summer camp," always shower them with water or insecticidal soap and plunge and drain them, to discourage pests and soil-borne diseases from coming back with them.
Use clean, porous pots for best results; they can always be put in cache pots. At the very least, provide drainage holes in containers. Repot plants to slightly larger pots in spring when they outgrow containers. Use fresh, newly-sterilized potting soil, and trim any roots that have grown out of the old soil to stimulate new, even top growth.
Use indoor plant fertilizer or mix a half-strength concentration of your garden fertilizer for your houseplants. Most plants need a dormant period during the winter, so begin withholding fertilizer gradually in late summer. Stop fertilizing in September, but continue watering plants as usual. Begin fertilizing in spring when plants start growing again. Always follow label directions, and never allow fertilizer to contact foliage.