Pawpaw

What is a pawpaw?

The pawpaw is a deciduous fruit tree from the custard apple family, Annonaceae, a family that is otherwise almost entirely tropical. Its relatives include the cherimoya, the soursop and the sugar apple. The pawpaw is the family's northernmost outpost: a tree of the temperate deciduous forests of eastern North America, at home in river valleys and moist woodland from the Gulf Coast to southern Michigan and Ontario.

Its fruit is oblong, green to yellowish green, and often hangs in clusters. Inside is a soft, pale yellow to orange flesh with two rows of large, brown, bean-shaped seeds. The taste is usually compared with banana, mango and vanilla custard. In German it is called Indianerbanane, Indian banana.

Origin and growth

The pawpaw grows as a small tree, according to Kentucky State University seldom taller than about 7.5 m. In full sun it forms a narrow pyramid with drooping, large leaves; in shade it branches more openly. In the wild it often spreads by root suckers and forms clonal patches in the understorey. It has a long taproot and fleshy, brittle roots with few fine root hairs, which makes transplanting difficult.

The dark red to purplish flowers appear in spring before or with the leaves. They are protogynous and self-incompatible, so a second, genetically different tree is needed for fruit. They are pollinated by flies and beetles.

Requirements

The pawpaw is hardy in USDA zones 5 to 8, down to about -26 °C. It needs a winter chill to flower, estimated at 400 to 600 hours for southern selections. It prefers slightly acid to neutral soil (pH 5.5 to 7) that is deep, fertile and well drained; heavy or waterlogged soil does not suit it. Its native climate is humid: Kentucky State University names at least about 800 mm of rain a year, falling fairly evenly with most of it in spring and summer. Young trees need consistent soil moisture, especially in their first two years.

Fruit, use and harvest

Pawpaws ripen from late summer into autumn, over several weeks. Ripe fruit yields to gentle pressure and has a strong fragrance. It keeps only a few days at room temperature; refrigerated, firm fruit can be stored for considerably longer. The flesh is eaten fresh with a spoon or used in desserts and ice cream. Skin and seeds are not eaten. Because the fruit contains annonacin, a compound shown in laboratory studies to be toxic to nerve cells, moderation is advisable.

In the food forest

In a food forest the pawpaw is one of the few fruit trees that fits naturally into the understorey and small-tree layer. Young trees need shade, which nurse trees can provide; older trees bear more as they receive more light. Its deep taproot and preference for humus-rich, moist soil make a thick mulch layer essential. Deer do not eat its leaves. In North America its leaves feed the caterpillars of the zebra swallowtail butterfly. Because it needs a pollination partner, it belongs in the plan as a small group rather than a single tree, ideally within a plant guild of taller trees and moisture-retaining ground cover.

In the Mediterranean climate

In Europe the pawpaw is still an experimental fruit. A 2021 review found scientific literature on its cultivation in nine countries outside North America, among them Italy and Romania. The best-documented European trial ran in Vienna, where 13 varieties were tested at Schönbrunn from 2003; the trees bore from about their eighth year, with yields and ripening times varying by variety and year. The Royal Horticultural Society notes that it needs long, warm summers to grow into a tree and fruit well, which the Mediterranean provides.

The difficulty in the Mediterranean is not heat or cold but water. A tree from humid forests with summer rain meets months of drought, strong light and dry wind. Irrigation, deep mulch and afternoon shade are therefore likely to decide success. Whether a mild Sardinian winter gives enough chill for reliable flowering has to be shown on site. The pawpaw is not on the EU list of invasive alien species; within a garden it can spread slowly by root suckers.

Propagation and care

Seed must never dry out or freeze and needs at least three months of cold, moist stratification before it germinates. Seedlings bear after five to eight years, grafted trees sometimes after three. Because of the taproot, pawpaws are best raised in tall containers and planted out young, in spring. Overloaded branches can break, so heavy crops are thinned.

How Terra Humana understands it

The pawpaw is something of a reversal at Sa Medada: a tree of a tropical family that comes from a cold-winter climate and must now learn to live with a dry summer. Terra Humana sees it as a candidate for the shaded, moister places of a growing food forest, where it may thrive under taller trees. Whether it can do so on a Sardinian slope is one of the questions the coming summers are meant to answer.