Climate:

Pawpaw inhabit the eastern woodlands of North America. They are found in ravines & on lower slopes, especially around streams. These lower, moist & shaded regions can be small & isolated. They are hardy zones 5-9 & can tolerate temperatures from -20 to 95+ °F. I've found conflicting information on this plants water tolerance, though. Some sources say pawpaw can't have wet feet & their wet soil must drain well. Others claim it can tolerate periodic flooding along waterways.

Some pawpaw plants grow in drier sites, or locations with different lighting. There is a difference between surviving & thriving. For fruit, you want a thriving plant. A 1985 study found that pawpaw throughout their varied range grow the tallest with the thickest trunks in shady moist locations.

Pawpaw tolerates black walnut allelopathy, wet soil as long as it drains, & some drought once established. 

Habits:

Pawpaw like to create colonies. They often create clones through root suckers. This means that even in some large pawpaw groves, the plants are all genetically identical clones. Isolation & cloning are thought to impact pollination & fruit yield. Many pawpaw thickets produce few or no fruit. Ridges like those found all over the Ozarks can prevent genetically different plants from coming into contact through pollinating insects. 

Castlewood State Park along the Meramec river is a good place to see large colonies of pawpaw. Although, there are many public parks in our area where you can see these beautiful trees.

Family:

Pawpaw are members of the Annonaceae family. Common name being the Custard apple & soursop family. They are distributed throughout the tropics of the americas. As you know, St. Louis is far away from the tropics. Plants in the Asimina genus are the only Annonaceae members that grow in temperate regions. There are 7 other members of the Asimina genus, but they only grow in southern states or Florida. Our pawpaw is the most cold hardy of the entire family.

Ecosystem:

Pawpaw are host plants for insects like the Zebra Swallowtail & Pawpaw Sphinx Moth. Zebra Swallowtail are a large & showy native that completely depends on the pawpaw. These 2.5-4" butterflies don't stray far from their host trees.

In 1980 researchers found that 57/64 insects found on pawpaw flowers were flies (Lagrange & Tramer, Ohio Academy of Science). Pawpaw are considered to have carrion flowers that draw in scavenger insects through their color & faint smell.

Pawpaw grow well with other lowland trees like Black Walnut, Sycamore & Black Gum.

The fruit is beloved by many humans, mammals & birds.

If you want fruit from your pawpaw, there are a few important things to know. The internet has a lot of confusing & very inaccurate information. Pawpaw have a low fruit rate &  more research still needs to be done on cultivating these plants. You need two genetically different pawpaw plants. They begin to flower around age 4-8. AND, it helps to know your way around a stamen.

Pawpaw are monoecious with perfect flowers, but can't self-pollinate. Each flower goes through a female phase, followed by a male phase. Flowers are around 1 inch & burgundy with 3 outer & 3 inner petals. Inside is a bumpy yellow mound that sort of looks like a lemon half with a green stem in the center. The green 'lemon stem' is the female structure, while the yellow becomes the male structure afterwards. Once flowers completely open, there are about 4 days that the female ovaries can receive pollen. If they don't, they fall off. About 11 days latter the flower is ready to produce pollen. Remember the yellow lemon bumps? They grow out, darken, become fuzzy & produce powder like pollen. Beetles & flies, including house flies, pollinate pawpaw. Although, some would argue that pawpaw reproduction was managed by Native American stewards. Trees will flower for 3-4 weeks in April or May. Flowers open in stages. I think this is what contributes to inaccurate information, because you can find flowers in their male phase & flowers in their female phase on the same plant. Plants with flowers that go through phases of female then male like this are known as protogynous.

In the 70's a group of researchers studied pawpaw fruiting in central Illinois. Out of 19,095 plants, only 0.4% produced fruit in 1976. The next two years, they studied the effect of hand pollinating pawpaw flowers. 4% of trees in 1977 produced fruit & 17% was achieved in 1978. That's a big enough jump, that I certainly plan to experiment with hand pollinating these unique trees. (Lagrange & Tramer, 1980)

Fruit grows green, then turns slightly yellow when ripe. Black spots on fruit can be caused by sunburn or wind. The flavor is compared to tropical fruits & banana. The texture is custard like. They have thin skin & don't transport very well. Although widely enjoyed in the past, it's thin skin prevents it from being a commercially available food today. It has a history of use raw, cooked or even as medicine.

Once the flower completes it's male phase, fertilized ovaries start to separate in the center of the flower. One flower contains multiple ovaries that can result in fruit clusters. Eventually the flower parts fall off, leaving any fertilized ovaries. Fruit matures mid August to late September. 

There are two major hypothesis about how such a tropical relative developed cold tolerance down to zone 5. One is that extinct, large mammals like giant sloths & mastodons ate pawpaw fruit & dispersed the seeds. The second is that pawpaw were cultivated by. native americans.

There is a history of meso-american agricultural technology moving throughout the americas. Corn is one example. Since colonization, foods developed by indigeonous farmers have become world wide staples: potatoes, tomatoes, chocolate, peppers, sweet potatoes, vanilla, peanuts & many more. The National Museum of the American Indian estimate 60% of the worlds current diet derives from these plants. More recently, lidar technology has led archaeologists in the Amazon to discover a large, ancient civilization. Previously, it was believed that the Amazon Rainforest was too dense to support a large city. Now researchers are looking into the possibility of the rainforest being a byproduct of ancient agriculture. I share these things to illustrate how advanced agriculture of the ancient americas was. It is entirely possible our pawpaw was intentionally developed by humans. This could explain how a tropical fruit relative became cold hardy.

The first written record of the name 'pawpaw' was in 1541. A Portuguese officer had made his way into the North American South. When he encountered Asimina triloba, he thought it resembled the tropical papaya fruit... One of many colonial misidentifications. In other parts of the world, papaya is still called pawpaw. In the St. Louis region, we use the term pawpaw to refer to our beloved native fruit.

In 1806, Lewis & Clark are known to have enjoyed pawpaw fruit. They were on their way back to St. Louis from their famous expedition. Pawpaw love to grow in river bottoms like those alongside the Missouri River. Lewis & Clark were returning at the perfect time of year & would have encountered many pawpaw groves with ripe fruit. This was a welcomed sweet treat after their long journey.

Thanks to a group of St. Louis students, the pawpaw became the official state fruit tree in 2019.

Today there is a lot of interest in foraging & growing these plants. Because of this interest, their low fruiting rate is being heavily scrutinized. I imagine the pawpaw's interesting history will only continue to accumulate.