The (Slightly More) Definitive Word on Pawpaw Trees

After the pawpaw question was raised at our last membership meeting, I did some online research into the propagation of the pawpaw tree. The pawpaw, Asimina trilobas, is an understory tree native to the eastern United States and parts of Canada, growing best in hardiness zones 5 to 8, so we are on the southern edge of its preferred geographic area.

Much of the research on pawpaws is being done in the Midwest, with a major research effort at Kentucky State University through their Cooperative Extension program. Their pawpaw planting guide starts with a disclaimer, “Very little scientific research has been done on Pawpaw. The advice given here is based partly on research and partly on the experiences of many Pawpaw growers.” Most of the information I found online from Kentucky State University is from the early 2000s.

So, do you really need to plant two pawpaw trees to produce fruit? According to the Kentucky State University experts, you need to plant two trees for cross-pollination, from two different cultivars or seedlings. The pawpaw flower cannot be self-pollinated because the stigma ripens before the pollen. The botanical term for this is protogynous (from the Greek roots for first and woman). By the time the pollen is shed, there is no place for it to go. Also, pawpaw trees usually require pollen from a genetically different tree to be fertilized—they are self-incompatible. If the trees that are being planted are from grafts, they will not be genetically different. If they are from seedlings, they most likely will be different. Pawpaw trees may produce many suckers, forming clusters of cloned trees with poor fruit production.