P. alato-caerulea (hybrid passionflower); P. caerulea (blue passionflower); P. coccinea (red passionflower, red granadilla); P. edulis (purple granadilla); P. incarnata (wild passionflower, maypop); P. jamesonii; P. quadrangularis (giant granadilla); P. racemosa, also called P. princeps (all called passionflower)
Bearing spectacular flowers, passionflowers make striking house plants when trained on supports. Outdoors in warm climates, the tendril-bearing vines grow 20 feet or more and provide an eye-catching cover for a fence or trellis. The open petals and sepals of the flower frame a crown fringed with filaments that in turn enclose a column bearing the reproductive parts. The flowers appear from late spring to early fall, depending on the species. In the tropics some species bear edible fruit, but they seldom develop in temperate climates.
The hybrid passionflower has three-lobed leaves and bears purple, blue, pink and white 4-inch flowers. Blue passionflower, which grows rampantly unless regularly pruned, can be used as a ground cover; the blue, white, purple and pink 3- to 4-inch flowers have a dark crown surrounded by paler petals and sepals and the leaves have five to nine lobes. Red passionflower bears scarlet flowers 3 to 5 inches wide, the vivid petals and sepals encircling a purple, pink and white crown; leaves are oval. The purple granadilla, with 2- to 2 1/2-inch white and purple flowers, has three-lobed leaves with toothed edges. The hardy wild passionflower, with fragrant 2-inch white or pale lavender flowers, has three-lobed toothed leaves. The fragrant giant granadilla has white, pink and purple flowers up to 3 inches wide and oval leaves. P. racemosa has deep red petals and sepals and a purple crown banded in white; its leaves may be lobed or unlobed.
HOW TO GROW. As house plants, passionflowers grow best with four hours or more of direct sunlight a day and night temperatures of 55° to 65° and day temperatures of 68° or higher. Plant in commercial potting soil and provide a climbing support. Keep the soil evenly moist. Feed the vine every two weeks with an all-purpose fertilizer applied at half the strength recommended on the label. When growth slows in the fall, stop fertilizing and let the soil dry slightly between waterings until new growth starts. In January cut the plants back to 6 inches to force new growth.
Outdoors, most passionflowers are hardy in Zones 9 and 10. Hardy to Zone 5 with protection, wild passionflower loses its leaves in colder regions, but is evergreen farther south. Plant plassionflowers in full sun near a support. They will grow best in a deep, moist, well-drained sandy loam that has been enriched with compost or leaf mold. Prune the vines heavily in fall or early spring to remove deadwood and to control rampant growth. Propagate additional plants from cuttings 4 to 6 inches long, taken at any time during active growth. Germination of seed is slow and uncertain.