We've had success with growing pawpaws, (Asimina triloba) preceded by a lot of failures.
I'll share some of what we've learned in the hopes that you don't have to make the same mistakes.
Planting:
It seems that pawpaws do not like people messing with their roots. Best results are obtained with minimum tap root disturbance.
Bare root trees can survive, but it's not an ideal way to plant pawpaws. The large tap root (expect at least 5x the height of the tree when young) is not very difficult to damage. Desiccating/damaging the tap root is the easiest way to kill/stunt your pawpaw tree. In our
experience only 1/4 of the bare root trees survived and they were very slow growing for the next few seasons.
Potted trees, in shallow containers, can have many of the troubles associated with bare root trees, the tap root is easily damaged when transplanting and it is almost always twisted around itself due to the shallow soil depth in these containers.
Potted trees, in deep containers, give you a good chance of success. It's best if the root hasn't reached the bottom of the pot.
Seeds typically require a full winter of cold stratification, and often will take two seasons to germinate. Never let the seeds dry out. Germination success falls rapidly if the seeds dry for even a few days. Do not freeze seeds.
Trying to root suckers hasn't worked. Transplanting wild trees has also been unsuccessful for us.
In the wild, I've noted that pawpaw stands are strongly associated with
deer trails, and I suspect that deer eating the fruit is a primary dispersal and scarification method for the species.
Cleaned seeds, cold-stratified (three months refrigerated in a zip lock with a moist paper towel or moist sphagnum moss), sprouted in warm (warm room temperature 70-75f), wet, paper towels have worked best for us. The tap root grows quite a bit before any green is seen. This is normal and not a cause for concern, don't expect to see much above ground until mid summer. Handle the sprouted seed gently and avoid damaging the tap root. If seeds sprout too early to plant directly in the ground, plant in a container that gives that root plenty of downward room to grow and try to plant it in its permanent location before the root hits the bottom of the pot.
Plant several trees. Pawpaws do not produce much (if any) fruit from self-pollination, I suspect they are generally self-infertile. You'll increase your fruit yield dramatically with several, genetically different trees. If you plant named cultivars (often grafted and genetically identical), plant a few different cultivars to ensure pollination. If you plant from seed, you'll be fine as long as you plant several.
This is not a fast growing species when young. It appears to put much of it's
energy into root production, in the beginning. After the third year there is a notable increase in the growth of the tree.
Soil:
Neutral to slightly acidic.
Heavy soils are reportedly not the best, but our pawpaws thrive in heavy clay as long as it's not an area that gets waterlogged. Pawpaws don't seem to do well in wet soil. The trees that we planted in our food plot, heavily amended with lots of
compost dug in, grew faster than those planted in the yard and only top dressed with compost. But it should come as no surprise that these cool temperate native trees thrive in loose, rich soil, heavy with organic matter and with good drainage.
Location:
Young trees require some shade for the first two years. We recycled old tomato cages covered on the south side with tied-on pieces of old, worn-out, white, bed sheets. Shade is an absolute requirement if you don't want a large percentage of your young saplings to die off.
After they have become established, Paw Paws thrive in full sun.
Plant close to other pawpaws for best fruit production, spacing requirements vary, but 10-15 feet should be fine.
Some growers have commented about a putrid scent from the flowers. I've never noticed this unless I stick my nose directly inside a flower, but if you are very sensitive, take this into consideration for your location.
Fruit:
As noted earlier, having several, genetically different pawpaw trees, in close proximity, will significantly increase fruit production.
Expect a minimum of five years before the first successful (and usually only a small amount of) fruit production. Some trees may fruit a year earlier, but the fruit is likely to drop before ripening. Older trees will produce significantly more fruit if there are plenty of pollinators (flies) and other pawpaw trees nearby.
Although it varies by climate, Paw Paws ripen in fall. Color is not a good indicator of ripeness. Fruit color varies between trees and fruit can be green, yellow, brown or mottled and still be ripe. Firmness is the best way to tell if a Paw Paw is ripe. The fruit is hard and feels woody when immature, it has a noticeable "give" to it when it is ripe.
Unfortunately, whole pawpaw fruit does not store or transport well. It is easily bruised and the time between ripe and rotten is short. This isn't a problem here as we immediately eat every ripe one we can pick. (When people say "yummy!" they're not kidding) But there are many recipes available
online, if you have a bumper crop. Pawpaw ice cream is particularly delicious.
Pruning:
We don't. In full sun the trees have an attractive shape and are fairly small, perhaps 20-25 feet here in SW Ohio. The fruit is easily picked with a commonly available fruit-picking pole if it is too high to reach by hand. The kind with a small wire cup with a few 90 degree bent wire fingers is my favorite. If the fruit resists a gentle tug, let it ripen a bit longer. Until you get a feel for your particular tree's fruit, it's best to do the "squeeze" test to check ripeness.
As an under story tree the shape will be more open and fruit production will be reduced. However, the tree does produce even when semi-shaded. This less full crown is typical of wild Paw Paws growing along with other tree species, which are usually faster growing.
Pests:
Occasionally we've noticed a small caterpillar that eats the flowers, I suspect this is Talponia plummeriana. It can reportedly eliminate an entire crop, but I've never had that big of an issue with this pest.
Some butterfly larva seem to eat the young leaves, but again, they don't seem to do
enough damage to bother the trees.
Deer will eat any low hanging fruit that they can reach, and fallen fruit is eaten by many creatures.
Weather damage:
Shade young trees (first two years) from strong sunlight, which will burn and often kill young saplings.
Mound some mulch (I like pine needles for this), for the first few winters, if you live in a cold climate. It's not uncommon for the above ground portion of a young tree to die off in very cold winters, only to re-sprout, in early summer, from the robust root system. In our area (USDA zone 6a) this has happened to a few (not all) first year trees during a particularly harsh winter. Those trees were in the open, unprotected from wind, and had no mulch or other protection.
It is also not uncommon for harsh winters to kill the tips of small branches, but they recover easily from the nearest viable bud.
Diameter seems to be the most important factor for pawpaw cold resistance. Thin saplings and branch tips (about half of the thickness of a pencil) are likely to suffer in severe cold weather. Thicker diameter trunks, twigs, and branches rarely have a problem. We've had cherry trees split in half, through the trunk and most of the branches, during one hard winter, but the pawpaws only suffered the above mentioned damage to thin branch tips and yearling trees. (All of which survived)
Strong winds don't seem to bother pawpaw trees which tend to flex and bend rather than breaking.
Overall our pawpaw trees require very little care, once established. Although, I do admit that they are a bit finicky to get started. Since we compost everything we can, we occasionally top dress with well-aged compost if we have some to spare. We did winter mulch the young trees with needles from under out pines and shaded them with some materials we've re-purposed, but that's didn't take much effort. The trees have never known a commercial fertilizer or insecticide and are doing just fine without them.
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Even if that happens once every five years, what a soil builder! Does this affect the next season's fruit or growth?
