Flowering houseplants can bring the warmth and cheer of a spring day indoors, even in the depths of winter. Most indoor flowering plants will need a sunny window and warm temperatures during the day, but cooler temperatures at night, so don't set them on a radiator or over a heating vent. Consistent watering and appropriate fertilizing and repotting according to each plants' needs will also keep your indoor plants flowering.
Gardenias (Gardenia augusta) need special care to grow and flower indoors, but their gorgeous white flowers which will fill your house with a heavenly perfume, set off by deep green glossy leaves, are worth the effort. Gardenias require an acid soil, according to the Texas A&M Extension. You can apply an acid fertilizer which is commonly sold in garden supply stores for azaleas, or incorporate your used coffee grounds into the gardenia container soil regularly. Gardenias need direct sun, but water and mist them frequently to maintain high humidity; they will drop their blossoms if they dry out or become too hot. Cooler night time temperatures, around 60 degrees Fahrenheit, will help prolong their blooming time. Gardenias can be moved outdoors to a shady patio during summer. A mid-winter rest in a cool, darker room for two or three weeks will also help re-invigorate the plant for a fresh round of blooming.
Geraniums (Pelargoniums X hortorum) have been favored flowering houseplants for generations. Their ruffled fan-shaped leaves come in varying shades of green, many with multi-toned striations; geraniums bloom in shades of white, pink, salmon and the classic bright red. The University of Kentucky Cooperative Extension recommends starting fresh plants from cuttings from your outdoor summer-flowering geraniums for indoor winter blooms, rather than bringing in plants which have been exhausted by blooming all summer. Geraniums start easily from cut leaves or ends of stems stuck in water or moist soil. Provide direct light--the Kentucky Extension recommends two to five hours of direct sunlight with bright reflected light all day--and temperatures around 70 degrees Fahrenheit. Water geraniums deeply until the potting medium is saturated, then allow them to dry out slightly between waterings. Promptly dead-head blossoms as they start to fade to encourage more blooms.
African violets (Saintpaulia spp.) have long been treasured, flowering indoor plants, both because they are available in an ever changing, seductively collectible array of leaf and flower shapes and colors, but also because unlike most flowering houseplants, they thrive in modest and indirect lighting conditions. Their dainty growing habit makes them an attractive accent to a desk or coffee table. According to the Penn State Cooperative Extension Service, African violets will grow and bloom under florescent lights or in an east or west window. Water African violets from below by filling a saucer under their pot with water, and add African violet fertilizer (available from garden supply stores) according to manufacturers directions. African violets are extremely easy to start from leaf cuttings stuck into damp peat moss.