Passiflora caerulea
Common Name: blue passionflower 
Type: Vine
Family: Passifloraceae
Native Range: Brazil, Argentina
Zone: 7 to 9
Height: 10.00 to 25.00 feet
Spread: 3.00 to 6.00 feet
Bloom Time: Seasonal bloomer
Bloom Description: Blue
Sun: Full sun to part shade
Water: Medium
Maintenance: Medium
Flower: Showy, Fragrant
Attracts: Butterflies
Fruit: Showy, Edible

Culture

Blue passionflower likes loose sandy or gravelly soils and does best when planted against a brick wall that retains heat during cold winter weather. Too much manure or compost will result in lush vegetative growth and poor flowering. This species will flower in a small pot, but it prefers plenty of root space and will do better in a roomy container. In Zone 8-9, the ideal location is against a warm south-facing old brick wall where an overhang prevents excessive drenching by heavy rains. Go light on fertilizer and water deeply, but infrequently; passionflowers should be encouraged to reach deep into the earth for water. When motivated to do so, they are capable of developing amazing root systems to sustain them though droughts and freezes. This vine is not winter hardy in the St. Louis area, and, if grown there, must be placed in an extremely protected southern location with the caveat that it may not survive the winter. Passiflora incarnata has much better survivability in St. Louis.

Passionflowers love high humidity, but they are subject to fungal diseases if they don’t get good air circulation in the greenhouse. Blue passionflower does better overwintered in a cool greenhouse where it can go semi-dormant as opposed to in a hothouse where it will be tempted to put too much energy into weak off-season growth. In either case, it is important to keep the soil on the dry side in the winter. Blue passionflower may be wound around a hoop support to keep it within bounds so that it may be grown as a houseplant in a sunny south-facing window.

Passafloras flower on new growth, so they may be pruned early in the growing season. It is best to cut some stems back nearly to the base, rather than just trim the tips. The terminal buds may be pinched out to encourage branching. Always keep some green foliage on the plant to keep the sap rising and encourage rapid regrowth. The roots may be weakened and become subject to fungal infection if too much top growth is removed at once. Don’t try to train passionflower to be too neat and compact; branches allowed to hang loose and droop a bit will be the ones most inclined to flower. Blue passionflowers will regrow from deep roots after even severe freezes. They have been known to survive temperatures as low as 5° F when the ground was frozen over two feet deep. It is nevertheless important to keep the soil as warm as possible, especially in the winter greenhouse.

Noteworthy Characteristics

Passiflora caerulea, commonly called blue passionflower, is a twining vine that can grow to 30 feet. The shiny leaves are usually lobed with five parts, but they can have as few as three lobes or as many as nine. They are evergreen in tropical climates, but deciduous where winters are cool. The white and purple-blue flowers which appear in summer may be as large as 4 inches across. They are followed by egg-size deep orange fruits from late summer through fall.

Genus name comes from the Latin words passio meaning passion and flos meaning a flower for the flower's symbolism of the crucifixion of Christ.

Specific epithet means dark blue.

Problems

Passionflowers are subject to a wide array of pests and diseases, but most of them have minimal impact on well grown plants. Butterfly larvae are the exception; caterpillars readily devour the foliage of healthy mature plants. Passionflowers and butterflies come together as a package deal. If you are going to grow passionflowers, and not turn into a pesticide-wielding fiend, you simply have to develop a philosophical attitude about butterflies and experiment to find strategies for sharing the foliage with them. If you are clever and lucky, you can figure out how to pick off just enough caterpillars to have flowers, fruit and butterflies, too.

Garden Uses

Blue passionflower is typically grown in tropical gardens or greenhouses for the exotic beauty of its flowers. This species is widely cultivated for its value as a parent plant in Passiflora breeding programs. The fruits are also edible. They aren’t very tasty raw, but they have a vaguely blackberry-like flavor and can be substituted in blackberry pie recipes.