Whatever their religious significance, there is no question that passion flowers are beautiful and strange, especially the species most commonly grown as a houseplant, P. caerulea. Passionflower vines have deeply lobed leaves with flowers that hang or peek out from the leaves. Some of the species have sweet and delicious edible fruit. Outside, passionflowers are grown on walls, fences, and trellises, where they are frequented by many varieties of butterflies. But make no mistake: Growing a successful passionflower is a bit like grabbing a tiger’s tail. They are robust, rampant vines under ideal conditions. and they may need frequent pruning to stay well behaved, even when grown as houseplants.
Light
Give these plants plenty of bright light, especially during the summer growing season. Full sun is preferable in the summer, with as much light as you can give during the winter.
Soil
When growing indoors, passionflower does well in an ordinary standard soilless potting mix based on peat moss.
Water
Keep these plants moist at all times during the growing season; you might have to water larger plants twice a day in the heat, especially if you move them outdoors for the summer. During winter, reduce watering but don’t let them dry out.
Temperature and Humidity
These plants can be quite warm in summer (household temperatures are fine) but like it a bit colder in winter months (down to 50 degrees Fahrenheit at night). Passionflower is fairly hardy, and even if they die back to the soil (such as may happen if you don’t move them indoors quickly enough in the fall) they will likely recover next spring. Passionflower does best with medium to high humidity, which can be hard to achieve indoors during the dry winter months. Misting or running a humidifier can help these plants.
Fertilizer
Fertilize the plants adequately during the growing season (about every month) with a controlled-release balanced fertilizer. When watering outdoor potted plants heavily in the summer, they may need to be fed more frequently. Feeding can be reduced in the winter.
Passionflower Varieties
There are several varieties of passionflower. In subtropical and tropical regions, these are used as butterfly and landscape plants, and collectors pride themselves on large collections.
For Indoor growing, by far the most commonly grown passionflower is the blue and purple Passiflora caerulea, which has a number of named cultivars.P. incarnata features blue flowers, with a more frilly appearance.Red passion flowers include P. manicata.
In general, the blue passionflowers are a bit more well-behaved in comparison to the red flowering species, which can be monstrously aggressive growers.
Pruning
Even grown indoor, passionflower may need to be pruned back when it begins to grow beyond its wire support. Late winter or early spring, while the plant is less active, is the best time for this trimming.
Propagating Passionflower
Passionflower is easy to propagate with leaf-tip cuttings. Take cuttings in the spring. Strip off a few leaves to expose nodes and bury the cutting in a moist seed-starting potting mix. Keep your seedling in a warm and bright place until new growth emerges. Rooting hormone is not necessary, as passionflower easily roots from cuttings.
How to Grow Passionflower From Seed
If you wish to start new passionflower plants from purchased or saved seeds, it’s best to first scarify the seed shells and soak them in water for a day or two. If you are saving seeds from a hybrid variety, remember that they will probably not “come true,” but will instead revert to the appearance of one of the parent species. Place the seeds on the surface of a pot filled with a damp potting mix. Don’t cover the seeds, as they need light to germinate. Place the pot in a sealed plastic bag and place it in a bright location. In 10 to 20 days, the seeds will germinate and sprout. Remove the plastic and keep the pot out of direct sunlight until there are true leaves. It’s best to grow the seedlings under a grow light during this time. The seedlings can be transplanted into larger pots when they are several inches tall with several sets of leaves.
Potting and Repotting Passionflower
Repot young plants every spring into a larger pot. Older plants can be stretched out every few years between repotting. To control their size, it’s best to cut your passionflower down in the fall, leaving only a few vines 15 to 20 inches long in the pot. Be aware, however, that plants trimmed in this way will still need to be repotted or at least refreshed.
Common Pests and Diseases
When grown indoors, passionflower can be affected by many of the same problems common to other houseplants, including scale, spider mites, and whiteflies. Neem oil or another horticultural oil or soap is the best way to control these pests indoors. Leaf spot, a form of fungal disease, can also occur if the plant is kept too wet. Remove affected leaves and treat the plant with a fungicide.
