The lovely passion flower (Passiflora spp.) is one of those plants that rarely fails to start a conversation on a walk through the garden. These stunning perennial vines can be grown in U.S.Department of Agriculture plant hardiness zones 7b through11, but be aware that most species are tropical in nature and will not tolerate sub-freezing temperatures. The eye-catching flowers come in a range of colors and sizes, and these interesting plants have many stories to tell.
The Passiflora genus comprises over 500 species, many of which are rare and endangered plants in rainforest habitats around the world. In addition, over 700 hybrids have been developed, and there are now passion flowers in almost every color of the rainbow and ranging up to 8 inches in diameter. The fascinating flowers produce copious amounts of nectar, attracting hummingbirds, butterflies, bees, bats and moths to do their pollinating. South America is the home of the greatest number of Passiflora species, though there is one native North American variety -- the maypop (Passiflora incarnata) which is hardy in USDA zones 7b through 11 and grows wild in the southeastern U.S.
Many varieties of passion flower produce edible, tropical-flavored passion fruit that comes in an astonishing diversity of size and color, as well. Some are eaten fresh with a spoon, though they are very seedy and most often used to flavor drinks and deserts. The giant granadilla (Passiflora quadrangularis) grows to the size of a football and is eaten like a vegetable in tropical countries. However, the classic passion fruit flavor comes from the purple passion fruit (Passiflora edulis) widely cultivated as a cash crop in Hawaii and other subtropical regions. Both species are hardy to about 30 degrees, growing in USDA zones 9 to 11.
Many insects seek to dine on the nectar produced by passion flowers, but others come to make a meal of the leaves. Incredibly, passion vines have evolved a defense mechanism to prevent their foliage from being decimated by pests. When an insect starts to chew on a leaf, a series of chemical reactions is unleashed, producing deadly cyanide that kills or wards off the majority of pests. For this reason, passion flowers are usually healthy and vigorous, making them a great choice as a low-maintenance landscape plant.
Butterfly Host Plant
Two species of caterpillars have co-evolved with passion flower plants and developed the ability to withstand the cyanide poisoning that all other insects succumb to. These are the larvae of spectacular butterflies -- the Gulf fritillary (Agraulis vanillae) and zebra longwing (Heliconius charitonius) -- that only use passion flower vines for their food source and reproductive needs. The butterflies feed on the nectar and pollen of passion vines and form their cocoon on the leaves. Then the caterpillars emerge to fatten themselves on the foliage, though fortunately their numbers never seem to overwhelm to the plant. Instead, they offer gardeners a window into the fascinating world of plant-insect cooperation.