Plant problems

Why Are My Pawpaw Leaves Curling?

Q: Can I grow pawpaw in the UK?

North American pawpaw (Asimina triloba) can be grown successfully in the UK, and it is one of the most exciting temperate fruit trees available to UK gardeners. Despite its tropical-looking foliage and its membership of the Annonaceae family (which includes the tropical cherimoya and soursop), pawpaw is native to the eastern United States and Canada, where it grows as far north as Ontario, and it is reliably winter-hardy across the UK. In the UK, pawpaw requires a sheltered, warm position with full sun; a south-facing wall is ideal, particularly in northern England and Scotland, where a long warm summer is needed to ripen the fruit. The flowers appear in spring before the leaves and are pollinated by carrion flies; in the UK, hand-pollination is recommended for reliable fruit set (the grower transfers pollen between flowers using a small brush, or hangs a small piece of meat near the flowers to attract native flies). The large, mango-like fruit (each one can weigh 200 to 400g) ripens in September and October in UK conditions in warm summers; in a cool summer the fruit may not fully ripen. Pawpaw does not fruit reliably when grown indoors; it needs an outdoor summer to build the energy reserves to flower and set fruit the following year.

Q: What does pawpaw taste like?

North American pawpaw (Asimina triloba) has a rich, tropical, custardy flavour often described as combining mango, banana, and vanilla, with a texture like very ripe mango or a very soft, creamy avocado. The custard-yellow or orange flesh surrounds two rows of large, dark brown, bean-like seeds; the flesh is sweet, fragrant, and melting when fully ripe. Pawpaw is the largest fruit native to North America and was a significant food source for Native American peoples and early European settlers; Lewis and Clark recorded subsisting on pawpaws during the Corps of Discovery expedition. Fresh pawpaw is best eaten within a day or two of picking (it bruises and deteriorates quickly), which is why it is almost never found in shops; home-growing is effectively the only reliable way to eat it fresh in the UK. The flavour has devotees who consider it among the finest fruit available and find it superior to imported tropical fruits; others find the intense sweetness and custard texture an acquired taste. Pawpaw ice cream and pawpaw bread (analogous to banana bread) are popular preparations in the American Midwest, where the fruit is celebrated at the annual Ohio Pawpaw Festival.

Q: How do I hand-pollinate pawpaw?

Pawpaw (Asimina triloba) flowers are protogynous (the female parts are receptive before the male parts release pollen, as in cherimoya) and require cross-pollination between flowers from different plants; a single isolated tree will not fruit. In the wild, the dark red, slightly fetid flowers are pollinated by carrion flies and beetles attracted by the smell. In UK garden conditions, hand-pollination is the most reliable method. Each flower passes through a female stage (stigmas receptive and sticky, anthers not yet releasing pollen) and then a male stage (anthers releasing yellow pollen). To pollinate: collect pollen from a male-stage flower on a small soft paintbrush and transfer it to the stigmas of a female-stage flower on a different plant. The two plants must be genetically different (grown from different seeds, or named cultivars); clonal divisions of the same plant will not cross-pollinate successfully. Alternatively, hang small pieces of rotting fish, meat, or shrimp paste near the flowers to attract native carrion flies; this works with varying reliability in UK conditions. Check the flowers daily during the flowering season (April to May in most UK locations) and pollinate whenever female-stage flowers are found.

North American pawpaw (Asimina triloba) is a member of the Annonaceae family (related to the tropical cherimoya and soursop) that is native to eastern North America and fully winter-hardy in the UK. Despite its dramatic, tropical-looking foliage and its reputation as an exotic, it grows as far north as Canada in the wild and is one of the most intriguing fruit trees available to UK gardeners. The large, paddle-shaped leaves are beautiful but vulnerable: late spring frosts and alkaline soil are the most common causes of leaf curl and yellowing on UK-grown pawpaw.

Late frost damage

Pawpaw's large, tropical-looking leaves emerge in spring before the risk of late frost has passed in most UK locations, and they are highly sensitive to cold once they have opened. A frost after the leaves have emerged causes the tips and margins to darken, the leaves to droop and curl, and the affected tissue to turn brown and papery as it dies. The damage can look alarming, but an established pawpaw tree will usually produce a second flush of leaves from dormant buds if the damage is not too severe. Young plants in their first two years are more vulnerable and may not recover from a hard late frost. The problem is most significant in northern and central UK gardens where late frosts are common into May.

What to do

Protect the emerging leaves with horticultural fleece during forecast frost periods in April and May. Position the tree in a sheltered spot that avoids frost pockets (cold air drains to low points in the garden; avoid planting in hollows or at the base of slopes). Remove frost-damaged leaves; the tree will produce replacement growth if the frosts were not repeated and the root system is intact. Young plants can be grown in pots and brought under cover when frost is forecast.

Iron chlorosis

Iron deficiency (lime-induced chlorosis) is a significant problem for pawpaw in alkaline or high-pH soils, which are common in parts of eastern, central, and southern England on chalk and limestone geology. In alkaline soil, iron becomes chemically unavailable to the roots even when it is present in the soil. The large leaves turn yellow between the veins while the veins themselves remain green (interveinal chlorosis); in severe cases the whole leaf yellows, browns at the margins, curls, and drops. Pawpaw grows best in slightly acidic to neutral soil with a pH of 5.5 to 7.0; in soils above pH 7.5 iron chlorosis is very likely to occur without management.

What to do

Test the soil pH before planting; if the soil is above pH 7.0, improve it by incorporating acidic materials (composted bark, sulphur chips, ericaceous compost) into the planting hole and the surrounding area. Apply iron chelate (sequestered iron) to established plants showing chlorosis; it is available as a liquid feed or granule and remains available in alkaline soils where standard iron fertilisers do not. Acidify the soil surface annually by mulching with composted bark and avoiding lime-based materials. In very alkaline soils, growing pawpaw in a large container filled with ericaceous compost and watered with rainwater avoids the problem entirely.

Drought stress

The very large leaves of pawpaw have a considerable surface area and lose moisture rapidly in hot, dry, or windy conditions. In a UK summer drought, or in a very exposed, wind-swept position, the leaves will wilt, droop, and curl as the tree struggles to maintain water balance. Young pawpaw plants (in their first two to three years) are particularly vulnerable to drought, as their root systems have not yet developed sufficient depth and spread to access moisture reserves in lower soil layers. Established trees are more resilient but still benefit from watering during prolonged dry spells.

What to do

Water young pawpaw trees regularly throughout their first three summers; apply a generous 10 to 20 litres of water per week during dry spells. Apply a deep mulch of wood chip or composted bark over the root zone to retain soil moisture. Choose a planting position that offers shelter from drying winds. Established trees in good soil rarely need supplementary watering in a typical UK summer; water during droughts of more than 2 to 3 weeks without significant rainfall.

Frequently asked questions

Why are my pawpaw leaves curling?

North American pawpaw (Asimina triloba) leaves curl most commonly in the UK because of late spring frost damage, iron deficiency (chlorosis) in alkaline soils, or drought stress. Late frosts after the leaves have emerged cause the tips to darken, droop, and curl; protect with fleece during forecast frost periods. Iron deficiency in alkaline soil causes interveinal yellowing, leaf curl, and drop; apply sequestered iron and improve soil pH. Drought stress on the very large leaves causes wilting and curling.

Can I grow pawpaw in the UK?

North American pawpaw (Asimina triloba) is fully winter-hardy in the UK (tolerating -20°C when dormant) despite its tropical appearance. It needs a sheltered, south-facing position in full sun; a south-facing wall is ideal in northern areas. The large fruit ripens in September and October in warm UK summers. Hand-pollination is recommended for reliable fruit set; you need two genetically different plants. It grows best in slightly acidic to neutral soil (pH 5.5 to 7.0) and suffers iron chlorosis in alkaline soils.

What does pawpaw taste like?

North American pawpaw has a rich, tropical, custardy flavour often described as combining mango, banana, and vanilla, with a texture like very ripe mango. The custard-yellow flesh is sweet, fragrant, and melting when fully ripe. It bruises and deteriorates quickly after picking, which is why it is almost never found in shops; home-growing is effectively the only way to eat it fresh in the UK. Pawpaw devotees consider it among the finest fruit available; others find the intense sweetness an acquired taste.

How do I hand-pollinate pawpaw?

Pawpaw flowers are protogynous: the female parts are receptive before the male parts release pollen. Cross-pollination between two genetically different plants is required; a single isolated tree will not fruit. Collect pollen from a male-stage flower on a small soft paintbrush and transfer it to the stigmas of a female-stage flower on a different plant. Alternatively, hang small pieces of rotting fish or meat near the flowers to attract native carrion flies. Check flowers daily in April to May and pollinate whenever female-stage flowers are found.