Known as the "Indiana banana" in the Midwest but simply as the pawpaw in other regions, this tree's claim to fame is producing the largest fruits of any tree native to the United States. Hardy to USDA zone 5, pawpaws can be grown from seed in virtually any home garden, provided the gardener has ample patience. Seed requires special care in order to germinate, and it can be nearly a decade after germination before the tree produces its first fruit.
About the Pawpaw Tree
The pawpaw tree (Asimina triloba) is a deciduous, understory tree of the southeastern United States, though its original range includes all of the United States east of the Great Plains and north to Ontario. Native Americans valued the tree for its fruit, a pale pink to greenish oblong fruit similar in texture and flavor to papaya. In fact, the pawpaw is the only temperate-climate member of the custard-apple family (Annonaceae); its relatives include tropical fruits such as the cherimoya, sugar-apple and ylang-ylang.
Fruit Set and Production
Drab, purplish-brown flowers appear on pawpaw trees in April or May, after which the tree leafs out. Trees are not self-fertile, and in the home garden, best fruit set is achieved through hand-pollination; native beetles and flies that are the trees' usual pollinators are inefficient and unreliable at best. Fruits take the entire season to ripen and are usually ready to eat beginning in late August.
Seed Appearance and Information
Enclosed within the soft-skinned, custard-like flesh of the pawpaw fruit are three to six brown seeds. The shiny seeds look very similar to enlarged, flattened kidney beans and are mahogany colored. Surrounding fruit flesh can be cleaned off easily, after which seeds should be stored in moistened peat moss. Seed intended for planting should never be allowed to dry out; this quickly kills the immature plant embryo within.
Seed Stratification and Germination
Grown from seed, pawpaw trees take anywhere from five to eight years to reach fruit-bearing size, and young trees are extremely slow-growing. But for growers with time to spare, producing pawpaw trees from seed is usually more successful than producing from transplants or grafts. Pawpaw seed needs a long stratification period, during which the seed is exposed to cold temperatures. Pawpaw seeds should be stratified either in soil outdoors or in the refrigerator at 32 to 40 degrees F for 90 to 120 days, after which they should be planted in a moist, sterile potting medium or sown directly into the ground. Because pawpaw seedlings first form a long taproot, up to 10 inches long, potted seeds should be placed in deep, specially designed sapling containers to give the developing taproot adequate room to grow.
Growing Pawpaw Seedlings
Seedlings emerge in late summer of the following year, usually sending up the first above-ground shoots in July or August. New saplings cultivated indoors grow best at temperatures of between 75 and 85 degrees. Once sprouted, new pawpaw seedlings should either be transplanted directly to a shaded location in the ground or potted up to a larger tree container. Yearling pawpaw seedlings cannot withstand direct sunlight, and will quickly succumb to burn if not provided with adequate shade. Older specimens, at two or three years old, can be grown in full sun, and copious sunlight is preferred for heavier fruit set.