Passiflora incarnata or passionflower is a perennial fast-growing vine from the Passiflora genus of around 550 species of plants and belongs in the Passifloraceae family. It is found growing wild near riverbanks, thickets, and near railroads and roadsides and is cultivated for both its fruit and outstanding purple-bluish blooms that open just for a day.
They grow almost 6–30 feet tall and around 3–6 feet wide the stems can be smooth or covered with downy hair, with palmate leaves of either 3 or 5 lobes measuring 2.4–5.9 inches. The flowers start blooming in July and are large and complex with conspicuous styles and stamens and are usually pollinated by several insects including carpenter bees and bumblebees as well as hummingbirds.
The oval fruit is about 2.5-3.5 inches long and 2 inches wide. It’s green at first, later turning yellow as it ripens. The fruits contain several seeds, each bounded by a fleshy covering containing edible juice that is consumed fresh or used as a flavoring in several processed food products. As with other plants in the species, the leaves are food for caterpillars of a variety of butterfly species, while the fruits are also eaten by wildlife. The roots can become dormant in winter, with growth resuming in May.
This is a low-maintenance plant that is usually trained to grow along fences and vertical arbors. In its native range of southeastern and central United States, the plant grows aggressively and can cover the floors of thickets within a few days under favorable weather.
The genus has been introduced for agricultural purposes in several areas of the world. When cultivating it for fruit harvesting, the plants must be spaced 36–60 inches apart from each other. It takes 1 or 2 years before they start bearing fruit that ripens in two or three months. The harvest depends on the age and size of the plant but an average of 10 to 20 fruits from each vine has been noted.
These plants like to grow under full sun and need 6 hours of exposure to direct sunlight. They will appreciate a bit of afternoon shade in very hot weather. Potted plants growing indoors need bright, indirect light.
These plants should have a deep, thorough watering when they’re first planted. After that, they will thrive being watered one or two times each week during their growing season.
They grow well under moderate to high humidity conditions. Keep the plants away from cold drafts in winter.
These plants enjoy warm weather and might need protection in cool regions during winter. They can grow all through the year in zones 7 to 11, however, in zones lower than zone 6, they will often die in winter unless they are brought indoors. Protected them from wind, as strong winds will damage their stems and burn their leaves.
These plants like well-draining, rich and moist soil, with a soil pH in the neutral to the acidic range. Adding compost will help supplement nutrients in poor soil and mulching plants growing outdoors will help the soil preserve moisture without the risk of becoming waterlogged.
Repot younger plants into larger pots every spring. Repotting older plants can be done every few years as their roots have already been established and are not spreading as rapidly as younger plants. To control the size of both the plants and the roots, cut down the plants in fall, leaving a few vines around 15 to 20 inches in length in the pot.
To successfully repot these plants, use rich potting soil and ensure the container has sufficient drainage capacity to keep the soil damp, but not allow the roots to get water-logged.
These plants are propagated by seeds, softwood cuttings, and tip layering (similar to air layering, but done in the soil). Softwood cuttings are usually used for propagation if you don’t like to wait for seeds to grow. Tip layering is an easier method of propagation as it involves the least effort on your part.
Take a 4- or 6-inch long cutting below a node and strip off all the leaves at the part of the cutting. Dust the cut end with rooting hormone. Prepare a container of well-draining soil and insert 1/2 to 1 inch of the cutting in the soil. Lightly water and keep the cutting shaded and warm and keep the soil moistened. Rooting will be done within 2 or 3 weeks, now transfer the cutting to a container or permanent location.
Select a healthy vine and remove any leaves and place the cleared portion of the vine on the ground or in a container filled with soil. Push it into the soil or cover it with soil to propagate. If the vine pops up, place a light rock on the soil to weigh it down or pin it to the soil with a garden pin. Once it has rooted and grown, separate it from the vine and transplant it.
While seedlings can be bought, these plants can be easily propagated from seed.
Collect the seeds in autumn when the fruit shrivels. Open the shriveled fruit and clean and dry the seeds before storing or planting them. Seeds germinate slowly, so start the seeds indoors by soaking them in warm water for one or two days to scarify them and discard floating unviable seeds.
Place the soaked seeds on top of a damp potting mix but don’t cover them as they require light for germination. Mist the soil to keep it moist. It might take 10 or 20 days for germination to begin. When sprouts appear, keep them away from direct sun until true leaves emerge. Harden off the seedlings for 10 to 14 days by slowly exposing them to outdoor conditions and extending their exposure to sunlight every day. Transfer them once they get large enough and have a few sets of leaves.
If you’re sowing them directly outdoors, wait until there’s no threat of frost and temperatures get to at least 55°F.
These vines need heavy feeding and benefit from regular applications of balanced fertilizer. Fertilize the plants in spring, repeating the process every 4 to 6 weeks until early fall. Plants growing in containers need more frequent feeding as they are watered more often and nutrients typically drain out from the soil.
Pruning is required just to keep the plant in check, to remove dead foliage and stems, and encourage healthy growth. In cool climates, the vines might die back in winter anyway, so they can be pruned down. These plants produce flowers on new vines, so prune them each spring before growth starts to flow through the season.
If you’re bringing a potted plant indoors in winter, cut the stems down, leaving the stems 1 to 2 feet above the soil before relocating them. In any case, they probably will become semi-dormant and look poorly, but they will perk up again in spring.
Provide these plants with some form of support for the vines—a trellis or even other plants.
Warmer and more humid conditions invite more pests that may attack these plants, including spider mites, scale, and whiteflies. Use insecticidal soap or neem oil to control infestations.
Leaf spot is a potential problem and is usually caused by a fungus. To treat the plants, remove infected leaves and treat the infection with a fungicide. Root rot is also a common issue in soggy soils that don’t drain well.
The leaves of these plants might become yellow for many reasons. Potted plants might wilt or turn yellow if they are under-watered or the weather is cold. Plants growing outdoors might develop yellow leaves due to a lack of nutrients.