Coleus are one of the rare plants that are grown almost exclusively for colorful foliage. In this regard, they're like crotons, but they're smaller and perhaps somewhat easier to grow inside. Coleus are truly in their glory in masses—their leaves are available in green, purple, orange, red, yellow, and in a striking array of patterns. Coleus are also fun plants to propagate; new plants grown from seed will be new creations. Although I've given directions to grow them year-round, coleus are often grown as annuals and discarded once they become leggy.
Light: Bright light, avoiding direct midday sunlight. Too much sun will wash out the colors in their leaves.
Water: Keep soil continuously moist throughout the year, but reduce watering in winter. High humidity is preferred.
Temperature: Above 60ºF is preferred in the summer. In winter, above 50º is best.
Fertilizer: Feed in spring with slow-release pellets or weekly during growing season with liquid fertilizer.
By cuttings or seed. Cuttings will be identical to the parent plant, but newly seeded plants will be variable. Plants grown for propagation, however, generally do not look as good as ones grown exclusively for their foliage. The energy of flowering usually saps the plant of some vitality, which is why many growers pinch off flowers.
A large coleus will reach only 2-3 feet. They grow rapidly in the spring, but many people don't overwinter them, so they never bother repotting the plant. If you choose to grow coleus for more than one season, you might consider trimming the plant back after the winter, refreshing the soil, and keeping it in the same pot. Alternatively, go up one pot size.
There are actually about 60 species of coleus, all native to Asia and Malaysia. However, virtually all of the coleus available are derived from the single C. Blumei species, crossed with a few other species. Hybridizing work within this group has been extensive—there are literally hundreds, if not thousands, of cultivars. Buy a coleus for its leaves and don't worry too much about its parentage.
Growing coleus indoors is definitely possible, providing you give it enough moisture, heat and humidity. If the plant goes into flower, snip off the unremarkable flowers to encourage vitality, and pinch off growing tips to encourage bushiness. Coleus tend toward brittle leginess, so they are best used in displays with other coleus or with other plants. If the plant starts to lose its leaves, it's probably too dark or cold. If the color washes out, it's probably getting too much sun.