Growing The Exotic Passionflower in Your Garden
Passionflowers are some of the most spectacular of flowering vines, especially because of their large and unusual flowers. The passionflower has been immortalized in Tennyson’s poem, “Song from Maude”:
There has fallen a splendid tear
From the passion-flower at the gate.
She is coming, my dove, my dear;
She is coming, my life, my fate.
The red rose cries, "She is near, she is near;"
And the white rose weeps, "She is late;"
The larkspur listens, "I hear, I hear;"
And the lily whispers, "I wait."
Despite their exotic beauty, passionflowers are not commonly grown, and I suspect few people in the more northern areas of the US have ever seen one—a shame, since one kind is hardy enough to grow in most of the US, and most kinds are easily grown from seed.
I grew up familiar with passionflowers because my mother grew the hardy kind—and grew them as Tennyson describes, near the garden gate. They shared space on the fence with perennial sweet peas, and since both are late-summer bloomers, the mixture made a spectacular show that was continually abuzz with bumble bees.
This is probably because, “flowers have a unique structure, which in most cases requires a large bee to effectively pollinate. The size and structure of flowers of other Passiflora species is optimized for pollination by hummingbirds, bumble bees, wasps or bats, while yet others are self-pollinating.” according to wikipedia.
Most passionflowers are graced with a corona that creates a sunburst of delicate threads, which give the flower its exotic beauty. Many passionflowers are also sweetly fragrant. In fact, at one time my favorite perfume was Crabtree & Evelyn’s “Passionflower.” So the flower has been immortalized both in poetry and in the perfumer’s art.
The only real downside to passionflowers is that they are not good cut flowers. Individual flowers are on very short stems and last only a day or two—that’s if they don’t start to droop right after you put them in water.
I never asked my mother how she came to grow passionflowers, or how she came to be the only person in the whole town—or the whole region, I guess—who grew passionflowers. They should be far more widely grown and enjoyed.
GROWING PASSIONFLOWERS FROM SEED
Most species of passionflowers are easily grown from seed. As with many perennials, germination can be a little slow. I’ve found that about half of the seeds will germinate in two to four weeks at warm temperatures. Some of the more exotic species germinate over a period from one to sixteen weeks.
Since most species of passionflowers are natives of the tropics, warm temperatures help germination. They germinate best when treated the same way you would treat tomatoes—by keeping the seed in very warm conditions to promote germination.
If seeds prove stubborn, J.L. Hudson, who carries seeds for several varieties of passionflowers, says, “Often a day or so of 110 - 120°F may trigger germination.” This would probably be most easily accomplished by placing the seed tray in a hot car with the windows rolled up, for a day. Hudson also suggests nicking the seeds to hasten germination. Some sources suggest soaking seeds for about 24 hours before sowing to help germination.
I’ve never resorted to any of these methods. I could probably get a higher germination rate by nicking the seed and providing a period of high temperatures, but I find that plenty of seedlings emerge without any special treatment.
Passionflowers grown from seed will not bloom until the second year. They require rich, well manured soil and plenty of water to be at their best.
PURCHASING PASSIONFLOWERS AS NURSERY PLANTS
Passionflowers—both the hardy and tender species—are often offered as nursery plants in many popular seed and nursery catalogs. The most commonly offered passionflowers are the hardy Passiflora incarnata, or maypops, and the slightly less hardy Passiflora caerulea, or blue passionflower.
There are many hybrid forms of passionflowers available as nursery plants (from specialty nurserymen). In fact, there are said to be over 700 known Passiflora hybrids and cultivars in existence, although only a few are available commercially.
One of the most widely available hybrid passionflowers is “Incense,” a hybrid of P. incarnata and P. cinnicata. Like the hardy passionflower that is one of its parents, it is hardy to around 0° and can be grown outdoors in the same climate range—even to Zone 4 or 5, with a heavy mulch.
In the North, tender passionflowers must be brought indoors over winter.
There are two passionflower species that can be grown outdoors in many areas of the United States. The Passiflora incarnata is said to be hardy to Zone 4 or 5, with a heavy mulch, and the Passiflora caerulea is said to be hardy to Zone 6.
Maypops, Hardy Passionflower (Passiflora incarnata)
The hardiest—and one of the most beautiful—species of passionflower is the Passiflora incarnata, or maypop. According to my mother, this kind of passionflower was a cornfield weed in Oklahoma, where she grew up. She said it was often called “wild pomegranate” because of its delicious fruits. In fact, this “wild pomegranate” was cultivated by the Indians.
The way to enjoy the fruit of the maypop is to bite a hole in the soft rind of the ripe fruit and suck out the seeds, which are encased in a juice-filled membrane, like real pomegranate seeds. The name “maypop” comes from the fact that the fruits will pop like a balloon, if you press hard on them.
According to J.L. Hudson, of jlhudsonseeds.com, Passiflora incarnata is hardy to Zone 4 or 5, if given a heavy mulch. I’ve found it to be perfectly hardy without any kind of mulch in northern Zone 6.
The Passiflora incarnata is also the medicinal species of passionflower. Passionflower herb from P. incarnata is official in the European Pharmacopoeia and is used to treat anxiety, insomnia, nerve disorders, heart palpitations, restlessness, and epilepsy, as well as high blood pressure. It also has analgesic properties and is included in many pain formulas when discomfort is caused by muscle tension and emotional turmoil, though it does not have strong pain-relieving qualities by itself.
The suggested dose is usually three or four cups a day of a tea of the herb..
This variety of passionflower has a valuable place in the medicine garden. The Passiflora incarnata is the primary medicinal species, although some other species have some of the same active alkaloids. It’s best not to use other species medicinally unless you are familiar with their particular uses. Some species have no known medicinal value, and others are at least mildly poisonous.
The hardy passionflower is one of the most beautiful late-summer-blooming vines, producing profuse gorgeous flowers in good soil In my area—Zone 6—the fruit does not ripen, except during unusually long, hot summers, though it might be possible to ripen the fruit more reliably if it were grown on a warm south-facing stone wall.
This species of passionflower is easily grown from seed. Germination is a little slow, taking two to four weeks—and longer, for all seeds to germinate. For me, only about half of the seeds planted germinate—though perhaps all would, given enough time. In any case, a small packet of seeds will produce many plants, even if you are a little impatient.
Oddly, this passionflower is often described as having two-inch flowers, but I have never seen one whose flowers weren’t at least three inches in diameter. The thread-like corona is a delicate lavender.
When grown outdoors in temperate regions, passionflowers die back down to the ground in winter and are slow to emerge in spring, so don’t expect overwinterd plants to produce new growth until very late spring.
Blue Passionflower (Passiflora caerulea)
The blue passionflower is almost certainly the one Tennyson wrote about, as it is and was commonly grown in England as a garden flower. It is said to be hardy in Zones 6-9, and it may be hardy only in southern Zone 6. I overwintered one of these plants outdoors during this past winter (in northern Zone 6), but it is still far too early to know if it made it through the winter. I also overwintered two plants indoors, which I’m eager to set out, as soon as the weather settles. These plants overwinter quite happily in a sunny window.
The blue passionflower produces larger flowers than the hardy passionflower, and the foliage is also more attractive. The vine can grow 10 to 15 feet high.
This kind is also easy from seed. As with the hardy passionflower, germination can be a little slow and erratic (two to four weeks), but one seed packet will produce several plants. For me, the blue passionflower seems to give slightly better germination than the hardy passionflower.
TENDER PASSIONFLOWERS THAT CAN BE GROWN BY NORTHERN GARDENERS, IF YOU’RE WILLING TO OVERWINTER THEM INDOORS
There are literally hundreds of species of passionflowers—far too many to begin to describe them all. I have listed a few favorites below.
The tender kinds—which would be all other species besides the P. incarnata and P. caerulea—can be grown in large containers and overwintered indoors. The plants can be moved outdoors after all danger of frost has passed. They should be grown in full sun.
Passionflowers bloom on new growth, so it is often advised that they be pruned fairly hard early in the growing season.
While several varieties of passionflowers are grown for their fruits, Northern gardeners will find that their growing season is not long enough to ripen the fruit. But the vines will still produce lovely exotic flowers.
Passionflowers, by the way, make fine houseplants and will remain happy in a sunny window almost indefinitely—though they will generally not bloom indoors, unless in a greenhouse.
Purple Granadilla Passionflower (Passiflora edulis)
This passionflower produces two-inch flowers with a purple and white banded corona. This vine grows up to 30 feet in height, and hardy only to Zone 7. Northern growers will need to overwinter it indoors, for sure. In the South, it can be grown for its delicious three-inch purple fruit.
Germination is from one to sixteen weeks. You may need patience to grow this one.
Pink Banana Passionfruit (Passiflora mollissima)
This passionflower is hardy to Zone 8 and produces pink or rose flowers that are about four inches in diameter and up to five inches long. Three-inch-long edible fruits are produced in climates with a long enough season.
This is a fast-growing vine that gives quick cover. Grown outdoors in Zone 8 or further south, the vine can reach up to 65 feet in length.
The seed germinates in three to twelve weeks.
Fragrant Passionflower (Passiflora actinia)
This beautiful and unusual passionflower is known for its sea anemone-like flowers in blue, white, and burgundy. It is also known for being highly scented. The vine will grow up to twelve feet in a season. It is hardy to about 24°.
Fragrant Passionflower (Passiflora maliformus)
Another passionflower called “fragrant passionflower,” this one has richly colored greenish-white and purple pendulous flowers that are huge—four to six inches in diameter. The flowers, as billed, are very fragrant.
Giant Granadilla (Passiflora quadrangularis)
This passionflower, with its spectacular flowers, is hardy only to Zone 10. The vines can grow 15-20 feet in a year, once established. It has large, fragrant flowers with deep red petals and a centre crown that contains five rows of numerous white and purple rays.
Grown in the warm climate of Zone 10, it can produce very large fruits weighing up to nine pounds. Like other passionflowers, it grows well in pots that can be moved indoors over winter in cold climates.