Something Rotten in Kentucky

Quick—What's the largest tree fruit native to the United States?

If you answered, say, "apple", "pear", or "peach", you're wrong. They're all too small and too Asian. If you said something like "the redwood", then you may have just missed the word "fruit" in the question.

The answer is a fruit few of us have actually seen, and even fewer of us eat on any regular basis: the pawpaw. I'm refering to the genus Asimina, by the way. Confusingly, outside of North America, the name "pawpaw" is applied to what Americans call a papaya (the name "pawpaw" is likely a corruption of "papaya", which itself comes from the Arawak word, "papáia".)

The pawpaw is the sole temperate member of the family Annonaceae, which features a number of other fruit species even less well known in this country, such as the atemoya, cherimoya, soncoya, sugar apple, soursop, and biriba. There are nine Asimina species native to the U.S., most of which are found only in the extreme southern areas of the country, mostly Florida. Two of them though, A. triloba and A. parviflora, are found in temperate regions, and it is A. triloba which has traditionally been viewed as the crop species.

A. triloba is a small, deciduous tree with large leaves, usually standing about 20 feet tall at maturity (though considerably taller specimens exist). The flowers are small and inconspicuous, appearing before the plant has fully leafed out for the year. Fruit are often borne in clusters of up to six fruits, but the exact number is highly depended on pollination. The fruit are roughly five inches long, and turn from green to yellow-black as they ripen. The flesh is white to yellow, and there are several large seeds in each fruit.

The texture and flavor have been compared to that of an overripe banana (hence the name "Poor Man's Banana") or to custard. I found it to be sweet and very distinctive, but not much like either bananas or custard. Pawpaws don't really keep well, bruising and decaying readily, a trait that has no doubt contributed to the lack of commercial production.

The thing I love about pawpaws, to be honest, is how some folks pollinate them. Like many fruit species, pawpaws are self-incompatible, and require another pawpaw of different genotype as a pollen source. Unlike most fruits with this problem, however, pawpaw flowers don't appear to appeal to bees. Some growers will hand pollinate, to assure a good crop, and while this is perhaps the most effective option, I prefer Plan B: rotten meat. It seems flies are the preferred agents of pollination for pawpaws, and what better way to draw a lot of flies to your pawpaw grove than a big heap of rotten meat. I may not be a fan of the fruit, but any crop that involves rotten meat in its standard culture is okay by me.

After years of mostly being ignored by academic research, the pawpaw is enjoying a bit of a renaissance. In 1993, Calloway stated the need for increased research efforts, particularly in expanding the germplasm resource, noting that only 19 cultivars were available. Calloway had instituted a pawpaw research program at Kentucky State University in 1990, which he handed off to Kirk Pomper in 1998. Thanks largely to the efforts of that program, there are now over forty cultivars available, and an ever expanding body of research on the breeding and cultivation of the species. KSU is still the only institution with a dedicated program for pawpaw studies, but the USDA maintains a germplasm program there and a handful of other universities maintain small projects supporting pawpaws, including Cornell. Interest in the crop is on the upswing, particular among hobbyists and backyard growers. Organic farmers are also interested in the native fruit because it can be grown without sprays (there are a few pawpaw diseases out there, but these are mostly minor and infrequent).

Pawpaws occur naturally all the way from Canada to south Florida, and thus should do well in most areas. So, if you're looking to add a little native flavor to your orchard, or an attractive ornamental to your yard, or just have a lot of old meat sitting around, maybe pawpaws are for you.

Update: It's been pointed out that the Kentucky State University program doesn't use the rotten meat strategy, and thus the title is probably inappropriate. But I can't think of another title, and I like this one, so it's staying.