The pawpaw (Asimina triloba) is the largest edible tree fruit native to the United States and grows wild in 25 states, including Iowa. Pawpaws grow wild in the rich, mesic hardwood forests of 25 states in the eastern United States, ranging from northern Florida to southern Ontario (Canada) and as far west as eastern Nebraska and parts of Iowa. It is the only temperate member of the Annonaceae family, which includes the delicious tropical fruits, sweetsop, soursop, and atemoya. In Iowa they are found in the wild in the southwest and southeast part of the state, usually as an understory tree. On the east side of Iowa they are found as far north as Jackson and Dubuque County.
There is a debate on whether the tree is actually native to Iowa or was introduced by Native Americans and/or railroad workers. Perhaps it is more than just a coincidence that many of the populations are found within 100 yards of an existing or former railroad right away. One theory is that railroad workers brought fruit up from Missouri and southern Illinois. In the process of eating the fruit they spit out the seeds and started new populations.
Pawpaw is a small, deciduous tree that may grow 15-30 feet high and 8-10 feet wide. In the forest understory, trees often exist in clumps or thickets, which may result from root suckering or seedlings developing from fruit that dropped to the ground from an original seedling tree. In sunny locations, trees typically assume a pyramidal habit, straight trunk, and lush, dark-green, long, drooping leaves that turn gold and brown during fall. Pawpaws are relatively free of pests; deer do not eat them, although they can cause rubbing damage.
Leaves occur alternately, are obviate-oblong in shape, glabrous, with cuneate base, acute tip, and prominent midrib, and may be 10-15 inches long and 3-5 inches wide. Vegetative and flower buds occur at different nodes on the stem, with flower buds being basipetal. Vegetative buds are narrow and pointed, whereas flower buds are round: both are covered with dark-brown, thick pubescence.
Flowers emerge before leaves in mid-spring. Blossoms occur singly on previous-year’s wood and may reach up to 1.5 inches in diameter. Individual flowers are pendant on nodding, sturdy, with pubescent peduncles up to 2 inches long. Mature flowers have an outer and inner layer of three maroon-colored, three-lobed petals. Flowers are strongly protogynous and self-incompatible, and require crosspollination, although some trees may be self-compatible. Pollination is by flies and beetles, which is consistent with the presentation appearance of the flower: dark, meat-colored petals and a fetid aroma. Fruit set in the wild is usually low and may be pollinator -or resource- limited, but under cultivation, tremendous fruit loads have been observed in Kentucky and other locations.
This delightful dessert fruit tastes somewhat like a very sweet banana while the texture is like a cross between a melon and banana. Fruit are oblong-cylindrical berries that are typically 1-5 inches long, 1-4 inches wide, and weigh 1-19 oz. They may be borne singly or in clusters that resemble the “hands” of a banana plant. This highly aromatic, climacteric fruit has a ripe flavor that resembles a creamy mixture of banana, mango, and pineapple. When ripe, skin ranges from green to brownish-black, and the flesh ranges from creamy white through bright yellow to shades of orange. In Iowa the fruit generally ripen in September, although it can range from late August to early October. Shelf life of a tree-ripened fruit stored at room temperature is 2 to 3 days. With refrigeration, fruit can be held up to 2 weeks while maintaining good eating quality. Within the fruit, there are two rows of large, brown, bean-shaped, laterally compressed seeds that may be up to 1 inch long. The fruit can be eaten fresh or the pulp can be used for a multitude of uses including ice cream, bread, and wine.
A replicated trial of 28 accessions was initiated in 1999 in Louisa County near Columbus Junction and a smaller trial was started in 2000 in Nashua. Trial results have indicated that pawpaw fruit can be grown in the upper Midwest and certain accessions were shown to have better potential for production. Some impressive performers in the trial include “Pennsylvania Golden,” an existing cultivar that ripens early and had the largest number of fruit, but each fruit was relatively small (about 6 ounces). A recently released cultivar “Shenandoah”, features midseason ripening, large fruit (many over 10 ounces), and low seed count. A later ripening cultivar recently released as “Susquehanna” bore large fruit (above 10 ounces) and had low seed count. It appears at least 10 years of growth are needed for trees to achieve full production of fruit. Yields are still being determined but it looks like each tree could produce in excess of 10 pounds of fruit. In general, it appears growth rates and potential yield north of HWY 30 will be less than the more optimum conditions south of HWY 30.
Pawpaw that is unrefrigerated has a shelf life of just a few days but refrigerated pawpaw will last about two weeks. The biggest hurdle for commercialization is devising a way to handle the processing to produce pulp. Currently the main way to separate the pulp from the seeds and skin is by hand which is uneconomical on a large commercial scale. There is ongoing research on ways to separate skin and seed from pulp by mechanical methods.
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Article by Dr. Patrick O'Malley, 2015