Growing
pawpaw, Asimina triloba,
By Kim Willis These articles are copyrighted and may not be copied or used without the permission of the author.
Many people are unaware of this native fruit tree that produces large delicious fruit, although that fruit has become a bit controversial. When the Spanish began exploring the interior of the North American continent they reported on the fruit (1541) and that indigenous people seemed to be cultivating it in places. George Washington and Thomas Jefferson were both quite fond of the fruit and grew the trees on their plantations.
The paw-paw tree makes a nice, somewhat tropical looking specimen tree and when it’s needs are met it produces a crop of large, tasty fruit with a custard-like interior with the taste of banana and cantaloupe mixed. The trees are resistant to deer, insect and disease damage. The fruit does not store or ship well though, so it’s never became a commercial crop although with the current interest in unusual and local foods there are people exploring that idea. It is a good backyard fruit tree for some gardeners. But before you rush out and buy a half dozen paw-paw trees there are some things you need to know and think about. Keep reading.
Paw-paw description
The paw-paw is a small tree, to about 35 feet high, that is native to the eastern half of the North American from southern Canada down through northern Florida although it does not grow naturally close to the coast. The paw-paw prefers moist shaded woodland edges and rich river bottoms. The trees put out suckers or clones and often grow as a thicket of genetically identical small trees.
The leaves of paw-paw are long pointed ovals, 10-12 inches long and 4-5 inches wide. They appear at the ends of the branches arranged in a symmetrical spiral around the twig. The veins and mid-rib are prominent. When young the leaves are somewhat hairy with a rusty tinge beneath. When mature they are smooth and glossy deep green with a slightly drooping habit. If you crush a leaf it has an unpleasant smell that reminds me of the nightshade family. The leaves turn a rich rust tinged gold in the fall.
The tree has a light gray bark that’s sometimes marked with paler blotches or small bumps. There is a tough, fibrous inner bark that Native Americans had many uses for, they made nets, matts and ropes from it. There is some speculation the trees may have been cultivated for that use as well as the fruit. The wood of a paw-paw is light yellow and spongey. Like the leaves damaged bark has an unpleasant smell.
Paw-paws bloom in early spring, before the leaves have expanded very much. The 2-inch flowers of paw-paw are marron or purplish red and bell shaped, facing downward or to the side. They have both sex parts, but like the apple, they are not self-fertile. Paw-paw flowers also have a bad smell, although they are not as smelly as gingkoes. They smell like dead meat and the pollinators are flies and beetles.
Paw-paws are said to need cross pollination with another paw-paw that is not closely related and those who want to grow them for fruit should plant two varieties of trees fairly close together. The paw-paws in those stands of clonal trees probably don’t pollinate each other because they are identical genetically. However, there is some controversy about this. People claim to hand pollinate their paw-paws by moving pollen from one flower on the tree to the next and get fruit. It’s possible that like apples, some paw-paw trees may have a genetic adaptation that allows some individual trees to produce fruit when helped with pollination. A flower can’t pollinate itself because the male and female parts of each flower mature at different times.
Paw-paw fruit is oblong and plump, and often occurs in clusters of up to 3 fruits fused at the base. Fruits are green when immature, ripening to brownish yellow in early fall. When ripe the flesh of the fruit is pleasant smelling, unlike the rest of the tree. Unlike a banana you can’t peel back outer skin. The ripe fruit is soft inside and yellow and is generally scooped off the rind for use. There are numerous dark brown, hard shelled seeds inside about the size of a bean.
A caution here I’ll go into more deeply later. Many people are allergic to paw-paw fruit. It can cause a rash if handled or if eaten it can cause hives and severe vomiting if you are allergic. Use caution when consuming your first paw-paw fruit. Cooking the fruit seems to intensify, not lessen reactions.
Cultivation of the paw-paw
Paw-paws are winter hardy to zone 5. They like rich loamy, moist but not saturated soil. They tolerate pH variations from mildly acidic to mildly alkaline – about pH 6-8. Plant paw-paws where you can irrigate them when dry, especially when they are young.
Paw-paws can be tricky to establish. In nature the seeds drop down on the ground to sprout or suckers pop up under tall grasses, weeds and shrubs. It takes several years for the young tree to reach above the undergrowth and receive direct sunlight. At that point they can handle direct sunlight if the soil is moist and more fruit is produced in full sun. But young paw-paw trees must never be placed in full sun situations, they quickly die. Adult trees will also do well in partial shade, particularly in the south.
Paw-paws greatly resent transplanting, the roots are quite fragile. So it can be difficult for the gardener to place the tree where it’s shaded when young but will get more sun when it is older. Most people get around this by providing artificial shade and lots of moisture for young trees and gradually reducing the shade or allowing the tree to grow out of it. Don’t keep the tree in a pot for long either, it will have a harder time adjusting after transplanting into the ground.
I used tree tubes to get my paw-paws growing. The sides are translucent, and I put fine black netting over the top, which was removed when the plants reached the top of the 4 feet tube. When the trees were a few feet over the tube top I removed that. Shade cloth t-pees are sometimes used.
It is always best to buy small, potted paw-paw plants rather than bare root plants. The best time to plant them is early spring while they are dormant, and moisture is abundant. Larger trees- more than 3-4 feet high are extremely difficult to establish. Digging paw-paws from the wild is also hard to do successfully, a large root ball must be removed around the roots of small trees and the tree re-planted immediately. Rooting cuttings of paw-paw is only rarely successful.
Paw-paws can be started from seed. The seed must have a cold stratification period to sprout. That means keeping the seeds in a moist pot of soil in temperatures about 35 degrees for at least 9 weeks. Seeds don’t store more than a year and still maintain good germination rates and they must not be allowed to dry out too much in storage. It takes 6-8 years for a paw-paw to produce it’s first flowers when grown from seed.
Gardeners should remember that paw-paws need 2 varieties to produce fruit. There are many commercial varieties now; 'Allegheny', 'Mango', 'Mitchell', ‘Overleese’, 'Potomac', 'Prolific', 'Rappahannock', 'Shenandoah', 'Sunflower', 'Taylor', 'Wabash', ‘Wells’ and ‘Zimmerman’ are some cultivars. Some are better for a certain area than others. Ask your County Extension office if they can recommend varieties.
Paw paws don’t need much fertilization. For the first 2 years after planting don’t fertilize at all. Once the trees are old enough to bloom a fruit tree fertilizer applied as the label directs can be added in early spring when you see buds and again in late spring-early summer if you see fruit forming. Don’t fertilize paw-paws in late summer or fall as it tends to cause new growth that will not harden off before winter.
Paw-paws don’t need much pruning either. Fruit develops on new growth so a light pruning when the plant is dormant can stimulate more fruit production. Remove unruly branches to shape the tree, crossing and rubbing branches. You may want to remove any sucker trees that pop up around the original tree if you don’t want a thicket developing.
Fruit from the paw-paw is ready to harvest when it is deep yellow brown and soft. It will slip easily off the tree. Paw-paw fruit does not store well, a day or two at room temperature and a little longer in the fridge. The flesh can be frozen and the fruit is sometimes turned into jam.
That disagreeable smell of paw-paw leaves and stems is from toxins called acetogenins. Because of the toxins paw-paws are rarely bothered by insects or even animal pests. One pest that can handle the toxins is Asimina Webworm Moth (Omphalocera munroei) caterpillars. It looks a lot like other webworms, it’s a brown caterpillar with a black stripe up the middle and little white spots. It makes a fine web on leaves, pulling them together for shelter. It’s uncommon and rarely severely damages the tree.
Another caterpillar, that of the zebra swallowtail butterfly (Protographium marcellus), uses paw-paw as a larval food. The toxins in the leaves protect the caterpillars from predation. These caterpillars do not cause any major problem for the trees.
Usually deer and rabbits don’t bother the trees. However, I had a tree damaged by deer browsing one winter so the rule doesn’t always hold true. Others have said goats and mules will eat the trees. Maybe they get a whopping stomachache and never do it again.
Uses and cautions for paw-paw
Yes, the fruit can be eaten, and paw-paw plant parts were
once used medicinally in various ways.
However, paw-paws also contain some very potent toxins. A natural pesticide made from paw-paw twigs
is being tested and it seems to be quite effective. But before you experiment you should know
that natural does not mean safe. This
pesticide is not selective, it kills good and bad insects and it may affect
other animals such as birds and earthworms.
Humans handling it need to be very careful and wear protective
clothing. It remains to be seen if the
product will pass EPA tests.
Recently research has found that paw-paw fruit has a high concentration of annonacin, a chemical that causes damage to the nervous system. A tropical relative of paw-paw, Annona muricata (soursop,or graviola) which also has high amounts of annonacin, is known to cause a Parkinson-like disease in those who consume a lot of the fruit or use parts of the plants for medicine.
Many people are allergic to paw-paw fruit. But it is also thought that eating more than one or two fruits at a time in those not allergic may cause gastrointestinal problems. Baking the paw-paw in bread or otherwise cooking it seems to increase digestive problems. The fruit is best consumed raw. The seeds should not be swallowed. They are high in toxins and while most would pass through the digestive system, if they don’t they might cause neurological damage as well as other problems.
Many people love the sweet flavor of paw-paw fruit but it’s a food that should be savored in small quantities. There are lots of anecdotes about people becoming very ill after pigging out on the fruit. Use care the first time you eat the fruit; an allergic reaction may cause vomiting or more severe symptoms.
It is thought that native people may have cultivated varieties of paw-paw that had fewer toxins than others. We’ll never know. Perhaps they just knew the limits to consuming and using paw-paw. Plant breeders are trying to see if the annonacin levels can be reduced by selective breeding.
There are old herbal remedies for many parts of the paw-paw. However only the most experienced herbalists should experiment with the paw-paw because of it’s toxins. Do not consume home remedies containing twigs, leaves, roots or bark that you find in old books, some of these are actually made with different species of plants called paw-paw as mentioned before. Even if they are for American paw-paw they could be very dangerous.
Paw-paw is thought to be safe when used topically- a recent research study found a mixture of pawpaw, thymol, and tea tree oil was found to be quite effective in killing head lice. Paw-paw may be used to treat wounds but once again beware of an allergic reaction such as rash or hives.
There are some research studies being done using various paw-paw extracts to destroy tumors and other types of cancers. These use carefully calibrated standardized doses and are generally injected. Do not experiment on yourself.
Despite some drawbacks paw-paws make lovely trees for the landscape and if you are lucky, you’ll get to enjoy some unusual fruit. Plant a couple and just enjoy them.
We have a park along the river that paw paw grows abundantly. I have noticed that in areas adjoining the pawpaw patches are very brushy but the paw paw stands are relatively devoid of brush. I was wondering if you know if paw paw are allelopathic ?
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