Passiflora aka Passionflower

Passiflora are fast-growing climbing vines that can reach 6-10 meters (20-33 feet) in height and similar spread when given appropriate support. P. caerulea typically reaches 10m, P. edulis 9m, and P. incarnata 6m. Growth is vigorous during the growing season, with vines climbing via tendrils that wrap around supports. In containers, restricting root growth can help control size and encourage flowering rather than vegetative growth.

Passiflora prefers daytime temperatures of 21-24°C (70-75°F) and cooler nights around 13-16°C (55-60°F). The temperature difference between day and night encourages blooming. Most species tolerate temperatures between 15-29°C (60-85°F) during the growing season. In winter, provide a cool rest period around 10-18°C (50-64°F). Hardiness varies by species: P. incarnata survives to -20°C, P. caerulea to -15°C, while P. edulis is frost-tender and needs minimum 10-16°C.

Passiflora thrives in moderate to high humidity, ideally around 60% relative humidity. Low humidity causes brown leaf tips and makes plants susceptible to spider mite infestations. Increase humidity by placing pots on wet pebble trays, using a cool mist humidifier, or misting regularly. Keep plants away from heating or air conditioning vents that dry the air. Good air circulation combined with adequate humidity helps prevent pest problems.

Feed Passiflora every 4-6 weeks from March to October with a balanced liquid fertilizer. Container-grown plants have higher nutrient needs than those planted in the ground. RHS recommends Phostrogen or similar liquid feed for potted specimens. For weak-growing outdoor plants, apply general fertilizer like Growmore in spring. Avoid fertilizing during winter dormancy. Over-fertilizing with high nitrogen can produce excessive foliage at the expense of flowers.

Passiflora produces its spectacular, intricate blooms from June through September. The distinctive flowers feature five petals and sepals with a prominent corona of thread-like filaments radiating from the center. Individual flowers typically open only in sunny weather and last just 24-48 hours. Blooms are produced on new growth, so adequate light and proper pruning are essential for flowering. Inadequate light is the most common reason for lack of flowers. Restricting root growth in containers also encourages better flowering.

The most commonly grown species include P. caerulea (Blue Passionflower), known for striking blue-white flowers and hardiness; P. incarnata (Maypop), the hardiest species with purple blooms and tasty fruit; and P. edulis (Passion Fruit), grown commercially for its delicious fruit. Notable cultivars include P. caerulea 'Constance Elliott' with pure white flowers, and 'Clear Sky' with large light-blue blooms. P. edulis cultivars like 'Black Knight' and 'Rainbow Sweet' are valued for fruit production. P. caerulea is often used as rootstock for less hardy species.

Passiflora can grow outdoors in USDA zones 7-11, depending on species. P. incarnata is the hardiest, surviving to -20°C (zone 5), while P. caerulea tolerates temperatures to -15°C (zones 7-10). P. edulis is frost-tender and only suitable for zones 9-12 outdoors. Plant in late May or early June after the last frosts in a sunny, sheltered south- or west-facing position. Protect from cold winds and consider wrapping stems with fleece in colder regions. Roots are often hardier than top growth and may regenerate in spring after frost damage.

Prune Passiflora annually in early spring before new growth begins. Since flowers are produced on new growth, pruning involves removing old flowered stems while retaining a framework of strong, healthy main stems. For renovation or overgrown plants, cut stems back to 30-60cm from the base every few years, though this may delay flowering for 1-2 seasons. Regular pruning keeps plants manageable and encourages abundant flowering. Avoid pruning in autumn or winter as this can damage plants before dormancy.

Repot container-grown Passiflora every 2-3 years in spring into a slightly larger pot. Use well-draining potting mix. Interestingly, passion flowers often flower better when slightly root-bound, so avoid overpotting. When roots become very crowded, move to a container just one size larger. For mature plants that have reached their final pot size, refresh the top few inches of soil annually instead of repotting. After repotting, water thoroughly and provide bright light.

Passiflora can be propagated by layering, cuttings, or seed. Layering is the easiest method and produces flowering-sized plants quickly. For cuttings, take 15cm softwood cuttings from young shoot tips in spring or semi-ripe cuttings in summer, including a heel of older wood. Root in moist compost in a heated propagator; expect rooting within 3 months with high success rates. For seeds, soak 12-24 hours in warm water, then sow in multipurpose compost at 20-25°C. Germination is slow and erratic, taking 1-12 months.

Yellow leaves on Passiflora typically indicate nutrient deficiency, watering problems, or disease. Nitrogen deficiency causes general yellowing, while potassium deficiency shows as scorched leaf edges. Overwatering suffocates roots and causes yellowing, as does underwatering. Fusarium wilt, a serious fungal disease, begins with yellowing leaves followed by leaf drop, branch splitting, and root death. Cold exposure can also yellow leaves. Check soil moisture and drainage first, then consider a soil test for nutrient levels. Yellowing with mosaic patterns may indicate viral infection.

Brown leaf tips on Passiflora typically indicate low humidity or underwatering. The dry air from heating or air conditioning causes leaf edges to brown and crisp. Increase humidity with pebble trays or humidifiers, and ensure consistent watering. Brown spots or patches may indicate bacterial spot disease (Xanthomonas), which starts as small round spots that enlarge and kill leaf tissue. Frost damage also causes browning. Ensure good air circulation to prevent fungal issues and avoid wetting foliage when watering.

Common pests include aphids, spider mites, whiteflies, scale insects, and mealybugs, which feed on sap causing leaf damage. Spider mites thrive in dry, stagnant conditions and leave telltale webbing. Nematodes can affect roots, particularly in P. edulis. Major diseases include Fusarium wilt (a deadly soil-borne fungal disease), cucumber mosaic virus (spread by aphids, causing yellow patches), and bacterial spot. Passiflora is notably resistant to honey fungus. Treat pests with insecticidal soap or neem oil.

Passiflora flowers are primarily pollinated by bees and other insects. The intricate flower structure with its prominent corona attracts pollinators. Flowers open only in sunny conditions and last just 24-48 hours, so timing is important. Some species are self-fertile while others require cross-pollination. For container plants or greenhouses lacking pollinators, hand pollination improves fruit set: use a small brush to transfer pollen from flowers open 12+ hours to newly opened flowers before midday. Passion flowers also serve as important larval host plants for butterflies.

Many Passiflora species produce edible fruit, with P. edulis (passion fruit) being the most prized for its delicious aromatic pulp with citrus notes. The fruit is eaten raw, juiced, or used in desserts and beverages. P. incarnata produces sweet yellow fruit with strawberry-pineapple notes. P. caerulea fruit is technically edible but has limited flavor. Beyond fruit, young leaves can be eaten raw or cooked, and flowers made into syrup. P. edulis seeds yield edible oil. Allow fruit to ripen fully (skin wrinkles) before consuming.

Passiflora incarnata has the strongest medicinal tradition, used as a sedative, antispasmodic, and antidepressant. It treats insomnia, nervous tension, anxiety, and irritability. The plant is not recommended during pregnancy and can potentiate central nervous system depressants like alcohol. P. caerulea contains higher levels of harmine, an MAO inhibitor. Other species have limited medicinal use. Always consult a healthcare provider before using Passiflora medicinally, as it can interact with medications and cause sedation.