Native Range and Climate

Pawpaws (Asimina triloba) are native to the United States, east of the prairies, and are generally found in the humid subtropical (Cfa) and hot-summer continental (Dfa) climate.  Only the earliest ripening pawpaws – such as Allegheny, Summer Delight, and Pennsylvania Golden – should be attempted in the warm-summer continental climate (Dfb) further to the north.

Within their native range, pawpaws tend to receive an average of 3" to 5" of rainfall per month throughout the year.  While they have been grown in mediterranean and semi-arid climates, they may require occasional irrigation during spring and summer if you wish to get them to fruit (or even survive).

Young trees (1 or 2 years of age) may require shade or filtered light, since exposure to full sun can damage or kill them.  Mature trees prefer full sun, but they are capable of producing some fruit in heavy shade.

Flowers

Pawpaws can bloom for up to 4 weeks, but each individual flower lasts for ~10 days.  Without hand pollination, fruit set can be low, since bees do not pollinate the flowers, flies and beetles do.  Male and female blossoms may easily overlap in the north, but I have heard of some incompatibility between earlier and later blooming trees in the south.  Unfortunately, there is very little information on varietal bloom times.

The flowers are originally female.  The petals will be partially green and burgundy in color when mature, and they will have a sticky pistil in the center with a bright green, plastic-like appearance behind it (the stamen) that shifts to a light tan color as it ages.  This should last for at least a few days (not sure how long), but then they revert to male and start to produce pollen.  At this stage, the stamen becomes a darker tan color and fluffs up like a lion's mane around the (now obsolete) pistil.

Harvest

Harvest season can last for up to 3 weeks (depending on the variety), and different people may prefer pawpaws in different ripening stages, since it can have a fairly dramatic affect on the flavor.  For the previous two reasons, as well as the available information being quite limited, it is fairly difficult for me to give the many different varieties a proper ripening label.  Regardless, I still have enough information for it to be of some use.

Weight

Common descriptions of some pawpaw varieties often imply that individual fruit generally weigh 227g to 340g+ (1 pound = 16 ounces = 454 grams), but this is somewhat misleading.  Many of these varieties typically produced fruit that weighed an average of 240g or less (sometimes much less), based on trials held at the University of Kentucky and Missouri.  Additionally, the average weight of a pawpaw appears to vary greatly based on the current (or even the previous year's) weather as well as the age of the tree.  Basically, consider the average weight of a variety, including those I give, to be a fairly rough estimate.

Pests and Disease

There are no serious pests or diseases that affect pawpaws, but out of those known to cause some damage, the pawpaw peduncle borer (Talponia plummeriana) is the most significant.  The adult moth is about 6mm in length^[1], while the larva is 5mm.^[2] Most years, they will thin out the flowers for you as they feed on them^[3], but some years, they may destroy enough to ruin the crop.^[2] The larva also feed on the roots, twigs, stems, and fruit (primarily around the seed).  Only 1-2 percent of the fruit have been observed to be affected, with no sign of it getting worse as the years progressed.^[3] Of those that were affected, only 1-5% of the flesh was damaged.^[1]

Pawpaw scionwood with dark channels through the pith might contain pupating larva, which may help spread the moth to other locations.^[3]

The asimina webworm moth (Omphalocera munroei) can be a nuisance in some locations, but they aren't a serious threat to anything other than the seedlings.  Their larva primarily feed on leaves, but they may girdle stems as well.

This doesn't really belong in the "pest" category, but caterpillars of the aesthetic Zebra Swallowtail butterfly (Eurytides marcellus) feed exclusively on the leaves from the Asimina genus.  They may cause problems for seedlings as well, but not to the extent of the asimina webworm moth.

Acetogenins

Acetogenins are possible neurotoxins with a link to atypical parkinsonism.  They are present in the entire pawpaw tree, but at a much lower rate within ripe fruit.  Furthermore, some varieties – such as Potomac, Sunflower, and Wabash – have lower concentrations than the others.  There are, however, over 50 different types of acetogenins, and the first correlation made between acetogenins and those who suffered from the affliction were not eating pawpaw, they were eating soursop (a relative of the pawpaw) and drinking a tea made from their leaves.  Acetogenins, or at least some of them, may also have some benefits.  They were demonstrated to be pesticidal, anti-tumor, anti-malarial, anti-viral, and anti-microbial.

Family: Annonaceae

Asimina triloba (pawpaw) is the only species within the entire Annonaceae family that can be grown within the warm-summer humid continental climate (Dfb).  Almost all of the others are either tropical or deeply subtropical.  Some of the pawpaw's best known relatives are the custard apple, cherimoya, soursop, and ylang-ylang, but they belong to another genus.  There are quite a few other Asimina species native to the southeast, one of which grows as far north as Virginia (Asimina parviflora), but there doesn't appear to be much interest in them, at this time.