Plant problems

Why Are My Passiflora Leaves Curling?

Q: Why are my passiflora leaves curling?

Passiflora (passion flower) leaves curl most commonly in the UK because of scale insect infestation, glasshouse red spider mite in hot, dry conditions, waterlogging of the root zone, or cold damage in winter. Passiflora caerulea (blue passion flower) is the hardiest and most widely grown species in UK gardens; a vigorous, tendril-climbing evergreen or semi-evergreen vine from South America that produces its spectacular, intricate blue and white flowers with their distinctive corona of blue-tipped filaments from June to October on established plants. In a warm, sheltered south or west-facing position against a wall or fence, Passiflora caerulea is reliably hardy in most of southern England and can grow very vigorously, covering a large wall within a few years. Scale insects (principally brown soft scale, Coccus hesperidum, and woolly vine scale, Pulvinaria vitis) infest the stems and leaf undersides of passiflora in sheltered, warm wall conditions; heavily infested plants produce honeydew, attract sooty mould, and the leaves curl, yellow, and drop. Red spider mite (Tetranychus urticae) thrives in the hot, dry microclimate against a south-facing wall in summer; infested leaves develop a fine, pale, stippled appearance on the upper surface, curl at the margins, and drop early, with fine webbing visible on the undersides in heavy infestations. Waterlogging kills the roots of passiflora rapidly; cold damage to the top growth in hard UK winters is very common, with the plant dying back to the crown and regenerating in spring.

Q: Is passiflora caerulea hardy in the UK?

Passiflora caerulea (blue passion flower) is the hardiest species of Passiflora commonly grown in UK gardens and is reliably hardy in most of England, Wales, and mild coastal areas of Scotland and Ireland. It is rated as hardy to approximately -10 to -12°C at the root zone in well-drained conditions; the top growth is much less frost-hardy and is typically killed or severely cut back in a UK winter, even in milder areas, but the plant regrows vigorously from the crown and base each spring. In the mildest parts of the UK (coastal Cornwall, Devon, the Isles of Scilly, coastal South Wales, coastal Northern Ireland), the top growth may survive through winter virtually intact and the plant can build up a substantial woody framework of stems over many years; in these conditions it can reach 6 to 10 m tall and wide and flower almost continuously from May to November. In most of southern England and the Midlands, the plant dies back to the ground or to a short woody stub each winter and regrows to 2 to 4 m in a single season; this annual regrowth means the plant flowers reliably each summer despite appearing to die each winter. In colder areas (northern England, Scotland, and exposed inland positions), the roots may not survive severe winters; growing the plant against a warm south or west-facing wall and mulching the crown heavily in autumn significantly extends the plant's northern range. Other Passiflora species grown in UK gardens are less hardy than Passiflora caerulea: Passiflora x violacea, Passiflora antioquiensis, and Passiflora quadrangularis need cool greenhouse conditions in most of the UK, though they may survive outdoors in the mildest coastal gardens.

Q: How do I prune passiflora?

Passiflora caerulea is pruned in spring (March to April) once the extent of winter die-back is clear and new growth is beginning to show from the base and from buds on surviving stems. The most important timing rule is not to prune in autumn; cutting back in autumn removes the stems that may protect the crown from winter cold, and in a cold winter the stripped crown is more vulnerable to frost than one protected by a tangle of old stems and dead growth. In spring, once you can clearly see where the new growth is emerging, cut away all dead, brown stems back to live wood or to the base. On plants that have survived winter with live top growth, thin out crowded stems to leave a well-spaced framework and shorten the remaining live stems to about half their length to encourage branching and more flower buds. Passiflora flowers on the current season's growth, so cutting hard back in spring does not reduce that year's flowering; vigorous regrowth produces long, flowering shoots from June onwards. In mild UK gardens where the plant has built up a substantial woody framework, an annual light thinning after the last frost (April) removes congested growth and maintains airflow; renovation by cutting the whole framework back to 50 to 60 cm from the base can be done every 5 to 7 years to prevent the plant becoming an impenetrable woody thicket. After flowering in autumn, the orange fruits that develop from the flowers can be left on the plant for ornamental effect; they are edible but bland compared to cultivated passion fruit.

Q: Why isn't my passion flower blooming?

Passiflora caerulea most commonly fails to bloom in the UK because the plant is too young, in too much shade, or has been fed too much nitrogen. Young plants (1 to 3 years old) typically do not flower well even in ideal conditions; flowering increases significantly in the third and fourth year as the root system matures. Full sun (at least 6 hours of direct sun daily) is essential for good flowering: passion flowers in shaded positions produce vigorous leafy growth but few or no flowers. Nitrogen-rich fertiliser (lawn feeds, high-nitrogen general purpose fertilisers) applied to the root zone promotes leafy growth at the expense of flowers; passiflora flowers best in relatively poor, freely draining soil without supplementary feeding. In some years, a long, cool, or wet spring can delay and reduce flowering; warm, dry summers typically produce the heaviest flowering. A position against a warm south or west-facing wall concentrates heat around the plant and significantly increases both the number of flowers produced and the length of the flowering season. If the plant is growing vigorously in a good position but still not flowering after 3 to 4 years, investigate whether roots are restricted (a large pot or a very restricted bed may limit the root system to the point where the plant cannot transition from vegetative to reproductive growth). Passiflora caerulea, once established and in full sun, is one of the most free-flowering climbers in UK gardens and should need no special treatment to flower well.

Passiflora caerulea (blue passion flower) is the hardiest passion flower for UK gardens, a vigorous South American climber that produces its intricate blue and white flowers with their distinctive corona from June to October against a sunny wall. It dies back to the crown in most UK winters and regrows vigorously each spring; the most common leaf problems in the UK are scale insects in sheltered wall conditions, red spider mite in hot, dry summers, and waterlogging of the root zone.

Scale insects

Scale insects, principally brown soft scale (Coccus hesperidum) and woolly vine scale (Pulvinaria vitis), are the most common pest of passiflora grown against warm, sheltered walls in the UK. The flat, oval, brown or waxy scales cluster on the stems and leaf undersides; in heavy infestations they coat the stems almost completely. The scales feed by extracting sap, producing sticky honeydew that drips onto leaves and surfaces below; sooty mould grows on the honeydew, turning leaves black. Heavily infested leaves yellow, curl, and drop prematurely; the overall vigour of the plant is reduced.

What to do

Scrub scale clusters from stems with a stiff brush and a solution of insecticidal soap. Apply insecticidal soap or horticultural oil spray to all stem surfaces and leaf undersides in late spring (May to June) when the mobile crawler stage (newly hatched juvenile scale insects) is most vulnerable; the crawlers cannot yet be seen with the naked eye but are present when the white, fluffy egg masses of woolly vine scale first appear. Repeat the spray every 10 to 14 days for 4 to 6 weeks. The hard spring pruning that removes most of the previous year's top growth also removes a large proportion of the overwintering scale population on the stems.

Red spider mite

Glasshouse red spider mite (Tetranychus urticae) can infest passiflora growing against hot, south-facing walls in summer; the mites thrive in the hot, dry microclimate created by wall-reflected heat. Infested leaves develop a pale, silvery-bronze stippling on the upper surface as the mites puncture individual leaf cells to feed; in heavy infestations, fine silk webbing is visible on the leaf undersides and between leaves; the leaves curl, yellow, and drop early. Spider mite populations build rapidly in dry, hot conditions and can reach damaging levels within 2 to 3 weeks of initial establishment.

What to do

Increase humidity around the plant by misting the foliage with water on hot afternoons; red spider mite dislikes humid conditions. Apply an insecticidal soap or neem oil spray to all leaf surfaces, particularly the undersides, repeating every 7 days for 3 to 4 weeks. Introduce the predatory mite Phytoseiulus persimilis for biological control; this predator is very effective in the warm, sheltered conditions of a south wall in summer. Avoid conditions of extreme water stress, which increase the plant's vulnerability to mite attack: ensure adequate watering at the root zone during hot spells.

Waterlogging

Passiflora caerulea comes from the seasonally dry hillsides and scrub of South America and requires very well-drained soil; its roots rot rapidly in saturated, poorly aerated conditions. In UK gardens, the most common waterlogging situation is heavy or clay soil against a wall that receives little rain (because the wall creates a rain shadow) but then is saturated by periods of heavy rain or excessive irrigation; the roots are alternately dry and waterlogged, which stresses them severely. Symptoms of root rot include wilting despite apparently adequate soil moisture, leaf curl, yellowing, and progressive shoot dieback from the growing tips downward.

What to do

Plant passiflora in well-drained, even poor and stony soil; add coarse grit to clay soils at planting. Do not plant in low-lying, poorly draining positions. The root zone against a wall can become very dry in summer (rain shadow) and then flooded in winter; check drainage around the wall base before planting. Water only when the top 5 to 7 cm of soil is dry; passiflora against a south wall often needs summer watering but needs almost no water in winter.

Cold damage

Passiflora caerulea is root-hardy to about -10 to -12°C in well-drained conditions, but the top growth is killed in most UK winters except in the mildest coastal areas. In cold winters, the shoots die back from the tips and the leaves curl, brown, and die; the plant then appears completely dead from October to April in colder UK gardens. This die-back is entirely normal and should not cause alarm; the plant regenerates from the crown and root system in April and May and can reach 3 to 4 m of new growth in a single season.

What to do

Do not prune in autumn; leave the dead stems to protect the crown through winter. Mulch the crown area heavily with composted bark, straw, or bracken in late autumn to insulate the roots from frost. In spring (March to April), when new growth is clearly visible at the base, cut all dead stems back to live wood or to the ground. A south or west-facing wall provides the thermal mass and shelter that most reliably allows the crown and low-growing stem framework to survive UK winters in colder areas.

Frequently asked questions

Why are my passiflora leaves curling?

Passiflora leaves curl most commonly because of scale insects (brown soft scale or woolly vine scale on the stems and leaf undersides in sheltered wall conditions), red spider mite (fine stippling and webbing on leaves in hot, dry summer conditions), waterlogging of the roots in poorly draining soil, or cold damage causing die-back of the top growth. Passiflora caerulea is very robust and regenerates freely from the crown after winter; most pest problems are manageable and the plant recovers quickly from damage.

Is passiflora caerulea hardy in the UK?

Yes, Passiflora caerulea is hardy in most of England, Wales, and mild coastal areas; it survives to about -10 to -12°C at the roots in well-drained conditions. The top growth is typically killed in UK winters but regrows vigorously from the crown each spring, reaching 2 to 4 m in a season. In the mildest coastal gardens, the top growth survives and the plant builds up a large, long-lived woody framework.

How do I prune passiflora?

Prune in March to April when new growth is visible: cut all dead stems back to live wood or to the ground. Never prune in autumn. On plants with surviving top growth, thin congested stems and shorten remaining stems by about half to encourage branching. Passiflora flowers on the current season's growth, so hard spring pruning does not reduce flowering. The spring pruning also removes much of the overwintering scale insect population on the old stems.

Why isn't my passion flower blooming?

The most common reasons are too much shade (full sun for at least 6 hours daily is essential), too much nitrogen fertiliser (promotes leafy growth at the expense of flowers), or the plant being too young (flowering increases significantly from year 3 onwards). Passiflora flowers best against a warm south or west-facing wall in poor, freely draining soil without supplementary feeding; in full sun with these conditions it is one of the most free-flowering climbers available for UK gardens.