Perhaps the finest ruellia for growing indoors is Ruellia macrantha, a 2- to 3-foot plant that bears rosy pink bell-shaped 2-inch blossoms in winter among 4- to 6-inch oval leaves. The two other species bear tubular blossoms; the 2-inch crimson flowers of Ruellia amoena bloom profusely year round atop wiry stems 18 to 24 inches tall; Ruellia makoyana, a trailing plant, is more often grown for its soft olive-green foliage, which has prominent silvery violet veins and purple undersides, than for its 1-inch, rosy red flowers, which bloom in fall and winter.
Ruellias do best in bright indirect or curtain-filtered sunlight, night temperatures of 55° to 65° and day temperatures of 68° or higher. Pot in a mixture of 2 parts peat moss to 1 part packaged potting soil and 1 part sharp sand or perlite. Keep the soil moist and fertilize every two weeks during the growing season; reduce water and omit fertilizer while plants are resting. Old plants tend to get straggly, so many gardeners grow new ones from stem cuttings in spring or summer. Watch for spider mites.