Growing Pawpaws in SE Minnesota: Twenty-One Years of Trial and Error
Purpose
I live in southeastern Minnesota USA, in USDA plant hardiness zone 4b. I started growing pawpaw trees back in 2003. Since 2008, I have been reporting on my progress in bits and pieces to various growers, gardeners' exchanges, and extension programs. I was featured in the Sept-Oct 2022 issue of Northern Gardener Magazine.
I grow my trees on a ⅕ acre suburban lot and have about thirty fruit-producing trees. I grow pawpaws because they fascinate me and because I like the fruit, which varies in flavor from tree to tree, some cloyingly sweet, others with a banana-mango flavor—sometimes with overtones of pineapple, lemon, or coconut.
I lack horticultural training, and possess, at best, an interested layperson’s level of familiarity with botany in general. But what I do works, and it’s time I write up what I’ve learned more systematically than I have in the past.
This report is specifically for horticulturalists and gardeners who know what a pawpaw (sometimes spelled paw paw, paw-paw, or papaw) is and want to grow them, but who live north of their native range, USDA zones 5 to 9.
Background
Pawpaw trees, Asimina triloba, like all members of the magnoliid clade, branched off the flowering plant or Angiosperm limb of the evolutionary tree before bees had established themselves, and their inconspicuous, green and purplish, yeasty-smelling flowers are pollinated by other insects, like beetles, flies, and ants.
To me, pawpaws look like transplants from an equatorial rainforest. Their relatives in the custard apple family, Annonacea, are all tropical. Pawpaws alone among them thrive in temperate climates. Pawpaws are true Americans, though — the largest, in fact, of any native American fruit. Their fruit has been eaten since time immemorial by indigenous peoples and it supplemented the diet of early explorers and colonists.
Pawpaw fruits, though, are rarely seen on supermarket shelves. They ripen within a few weeks of each other. They don’t keep well, and they bruise. As a result, big-box grocers can’t make money on them. If you are ever lucky enough to eat one, you or a friend likely picked it.
The Challenge
The long and short of this report is that yes, many pawpaw specimens can survive zone 4b winter temperatures. Some might even manage 4a or 3b.
The challenges growers face, though, stem not just from the cold itself, but also from fall/spring temperature variations and periodic hard freezes the plants experience as they are dropping into, or coming out of, dormancy. Under these conditions, many specimens take extra damage — from the loss of many buds to death of the crown.
Of those that can tolerate these conditions, only a subset (maybe two thirds) produce fruit that ripens reliably during our short growing season. To fully mature, the fruit needs at least 150 frost-free days. For the quantitatively inclined, the threshold is 2500 growing degree days (base=50). All cultivars I know of need that much at least, and although we accumulate more than 2500 GDD in a typical year, that accumulation isn’t complete until sometime in September, when the first frost looms and I’m worrying about whether my fruit will make it to the finish line.
Despite the cold winters and short growing seasons, many pawpaw specimens thrive and produce fruit in USDA zone 4b. The only practical way to know which ones is to plant and replace, plant and replace, until you end up with a workable orchard.
Getting Started from Seed
If you are in a hurry, it is not necessary to grow from seed.
I like growing from seed, though, because at this point (2023) I have my own supply of fruit and can therefore be sure of where my seeds came from. My seeds get collected in September or October (assuming we haven’t had a frost by then), from mature plants that I hand-pollinate in April or May. I generally only save the seeds of cold-tolerant plants that produce large, tasty fruit that ripens early enough for me to harvest and eat it, and that possesses just a single row of seeds.
If you are just starting and you want to grow from seed, you can purchase seeds from a northern grower, collected from plants known to tolerate cold winters. If you obtain seeds directly from fruit, clean them thoroughly (dish soap is sufficient). Do not dry them the way you would most other seeds. Store them at around 4 or 5 ºC (40 ºF) in a plastic bag with a small, moist section of paper towel. Leave them there for at least three and a half months.
There is no need to process them additionally (e.g., scarify them).
I usually place my seeds in my refrigerator’s dairy or cold cut drawer, where the risk of accidental freezing is low, and where I can forget about them until February. In February I remove the seeds from the refrigerator and plant them three-quarters of an inch (2 cm) deep in ten-inch (~25 cm) tree-seedling pots, in standard potting soil. The seeds send down a few inches of taproot before anything is visible above ground. When they are five or six inches (15 cm) tall, the seedlings are ready to be planted out. The taproot by then has normally reached the bottom of the pot. The whole process takes three or four months.
I have often given up on seeds and thrown them onto my vegetable garden along with the potting soil I planted them in, only to find them poking their heads up in late July or August.
Pawpaws lack the fine root hairs that most flowering plants possess. As a result, when you plant them out, most of the dirt tends to fall off. But don’t worry. If the area where you are planting them is moist and rich in organic matter, they’ll be OK…for the moment.
They also have no trouble growing under black walnut trees (which not all plants can do, on account of the juglandin such trees produce).
Although pawpaws tolerate both shade and hot summer days > 38 ºC (~100 ºF), and are unpalatable to deer and most parasites, they benefit early on from weeding, composting, mulching, and protection from ultraviolet light.
Regarding UV light: I usually put a cage of chicken wire around seedlings, wrapped in clear plastic. That or I just use a fifteen-inch tree tube (see photo). Although some seedlings are more sensitive than others, they all seem to tolerate full sun by the time they reach 40 cm (a little under a foot and a half) or have simply grown over the top of their tree tube.
Although they can grow in shade (in the wild, they are understory plants), pawpaws produce more fruit if they get at least a few hours of full sun.
Japanese beetles sometimes feed on pawpaws, especially if tastier hosts aren’t handy. If Japanese beetles become a serious problem, neem oil and diatomaceous earth can reduce their numbers to tolerable levels. Zebra swallowtail butterfly larvae also feed on pawpaws. But I have never seen one on any of my trees, and if I did, I would leave it alone. I like them.
Even under optimal circumstances and lots of love and care, northern gardeners will likely lose at least a few pawpaws in the first few years, often more. Out of the hundreds of seedlings I have given away to friends and random strangers who reached out, I would guess maybe a dozen survive. Most people don’t do everything I tell them to. Even those that do lose many plants. Many never come back, discouraged. I reassure those that do return, and I give them more.
Other Ways of Getting Started
Gardeners looking to jumpstart their pawpaw-growing project may want to order more mature dormant plants. The challenge with dormant plants is that they typically ship from a milder climate, and, by the time the plants are completely dormant and arrive in USDA zone 4, the ground is likely to be unworkable. Another issue with this approach is that you may receive specimens that are, despite being bare of greenery, only partially dormant. Although being partially dormant would not be a problem in a climate comparable to that of the origin nursery, such plants may suffer when moved to zone 4.
One solution to this problem is to order in the spring. Just keep in mind that, because the ground can’t be worked until relatively late in zone 4, and because pawpaws are slow to leaf out anyway, you may not see strong growth until well into the summer. And at that point, one has to wonder whether it makes more sense just to purchase and plant fully leafed-out specimens.
Transplanting fully leafed-out specimens in the summer is something I have tried exactly five times. What I did in each case was to order a healthy three- or four-year-old specimen and set it out in August — in time to get settled in for the fall. Even though pawpaws send down a deep taproot that may not develop properly in container-grown specimens (or that will be partially severed if field-grown), I have had some luck doing things this way — with two of the five plants still surviving. The main challenge when it comes to summer planting is finding a reliable grower who will ship strong, non-dormant plants that are packed sufficiently well to escape serious damage during shipping.
Whether you plant nursery-supplied specimens in the summer, dormant ones in the spring, or set out your own seedlings whenever they are ready, keep the trees watered and weeded until they go dormant in the fall.
Winter Dieback
After planting, you may notice several inches of dieback when the trees leaf out in the spring. Hardy specimens will recover quickly from damage. I own several specimens that suffer little or no dieback at all now, depending on the winter. Specimens old enough and strong enough to flower well in the spring seem to suffer less damage than younger ones. Older specimens also tend to ease into dormancy earlier than younger ones, ceasing new growth by August (as opposed to vigorous young specimens, and some root suckers, which may continue strong growth until the first frost hits, in late September or early October).
You can tell when a pawpaw is done growing for the year because it sets a stunted, brown terminal bud on all its branches. These buds have a distinctive look that all pawpaw aficionados recognize. The buds say, “I’m finished now. Time to ripen fruit and think about next year.”
Although there exists variation between specimens, pawpaws are slow to break dormancy. In Minnesota, the flowers often don’t open until early or mid May, and the leaves come later. The lateness helps protect the trees from late frosts.
But even before they fully break dormancy, our variable weather patterns in Minnesota can stress the trees. Insufficient summer and fall rain in some years also seems to weaken them as they head into dormancy in the fall, leaving them susceptible to damage both then and also later, in the spring.
Grafted Cultivars
When you’re starting, don’t bother with grafted cultivars, at least not at first. I’ve had no success at all with grafts, or with grafted cultivars specifically.
I’ve tried three cultivars:
- NC-1
- Pennsylvania Golden
- Davis
All scions died back down to their rootstocks within a few years, and I never saw flower buds. I’d have thought the NC-1 (a northern cultivar) might have been more cold-hardy, but there are many factors at work here, and I don’t know how the rootstock plays in. I recommend just purchasing select, vigorous non-grafted specimens.
I often remove specimens that don’t taste good (e.g., that are cloying or have a bitter aftertaste), or that damage too easily. If you are in this for the long haul, try to be dispassionate.
Pawpaws in my yard don’t produce significant numbers of flowers until they are at least six feet tall (about 2 meters). Flower buds are easy to discern. They are rounder than leaf buds. You’ll recognize them when you start to see them after four to six years of seeing only leaf buds on a given tree.
The year after I started to see the first flowers on my trees (2013), I pollinated them using a male-stage flower from a Pennsylvania Golden specimen. I chose that particular cultivar because, even though its taste isn’t top-notch, it ripens early. I wanted to increase the chances that the early ripening trait would be passed on to anything I grew.
Other Propagation Methods
Pawpaws are challenging to propagate by means other than growing from seed and transplanting.
Rooting pawpaws, for example, is difficult, even with hormone-infused rooting powder. Pawpaws also require skill to graft. I have watched both Tom Wahl and Sheri Crabtree graft. I have all the equipment and have tried many times to do it myself, with no success. As I’ll explain in more detail later, grafts always fail for me within a few years, both mine and others’.
Pawpaw root suckers are also tricky to propagate. They typically lack well-developed root systems. If your timing is good, you can sometimes sever their connection to the main trunk once the sucker stands between one and two feet tall but has not yet grown a deep taproot. After severing, you can then wait for the sucker to strengthen, uprooting and replanting it once it has started to grow. If the area where you plant it is rich in organic matter and moisture, it stands at least a chance of establishing itself. I know this is possible because I have a neighbor, an amazing horticulturist who lives two houses north of me, who managed it.
I would not recommend this technique for most people.
The main way pawpaws reproduce in the wild is by vegetative self-propagation, specifically, by suckering. The resulting clonal patches can cover large areas, but because the clones are all genetically identical, they don’t always produce fruit. There has to be a genetically different pawpaw in the area.
If you don’t mow around your trees, they will convert your entire yard into the fabled pawpaw patch.
Pollination and Fruiting
After your plants are five or six years old, you may begin to see small purple flowers emerge early in the spring. Don’t allow the plants to fruit initially. Wait until they are at least seven feet tall. Until then, pinch off the flower buds in the spring. Tom Wahl of Red Fern Farm in Iowa (USDA zone 5) tells me that allowing pawpaws to fruit too early can retard growth. But once your plants reach an appropriate size and are flowering profusely, hand-pollinate them.
To hand-pollinate them, check for fully open flowers. If you see lots of pollen when you peer inside a flower, it is in its male stage.
The flowers are dichogamous, having separate female and male phases, and protogynous, meaning that the female parts, the pistils, mature first. Male flowers therefore come last, and they are typically darker colored and have a wider, more open corolla than their female-stage predecessors.
To pollinate, swab the inside of a male-stage flower with a brush then walk over to another plant and, with the same brush, swab the inside of any female-stage flowers you see. My full procedure is actually a bit more elaborate than this. I knock pollen from my favorite trees with a brush into a custard dish and then walk around, periodically dipping the brush back in, swabbing female-stage flowers on all my trees as I go, using a ladder as needed to reach them.
Don’t overdo pollination because it’s easy for trees to become overloaded with fruit. For some specimens, that can lead to broken limbs. In my yard, plants that produce the best-tasting fruit seem to take the most limb damage, and although I would like to eliminate this latter trait, with only thirty or forty trees and limited time and space, accomplishing this has posed challenges.
Note: If you have only one flowering plant, you’ll need to ask a friend in a milder climate to send you a flower. Pawpaws do not self-pollinate well, if at all. As described earlier, I did this in 2013. A friend with an orchard mailed me a flower from one of his Pennsylvania Goldens.
I had also done something similar the previous year, the first year I had ever seen a pawpaw flower bud. I clipped a flower from a healthy wild pawpaw at East Wind Community in southern Missouri, where my son lives (USDA zone 6). The flower was picked on March 23. Spring arrives earlier in Missouri than in Minnesota, so it was easy finding a mature flower, even though everything was still dormant back home. I took the flower back to Minnesota and put it in the refrigerator.
Two weeks after putting the flower in my refrigerator, I removed it, a bit mushy, moldy, and with a startled pawpaw peduncle borer, Talponia plummeriana, wriggling around—which I squashed. Due to warm March weather that year, our largest (then nine-foot) pawpaw’s flowers were already opening (early April), and I swabbed them with pollen from the Missouri flower.
Two hard frosts then followed on April 10th and 11th (~26º F), plus another less severe frost on the 13th. In the aftermath of these hard frosts, perhaps weakened by a late summer and fall with relatively little rain, three of our five still living pawpaws died back almost to the ground, but luckily not the one I’d pollinated. I had no realistic expectation of any fruit and didn’t even think to look for any.
On June 10th I happened to be double-checking for dieback. I was shocked to find eleven fruits developing.
Harvesting
Pawpaws don’t change color much when ripe. They sometimes get yellower and start to smell sweeter when they’re ready. They also get softer, so if you are patient, you can squeeze each fruit to see if it’s ripe. The best way to check, though, is to walk up to a mature tree, shake it hard and see what falls off.
I am not joking. Truly, this is the best way.
Eat pawpaws raw by splitting them in half and scooping out the custard-like insides with a spoon. I don’t care for the skin. Some people don’t mind it. Don’t eat the seeds.
I don’t recommend pulverizing or blending pawpaws. Eating pawpaws in this form makes some people sick. Chopping them coarsely is OK. A typical way to eat them, if you don’t eat them raw, is in ice cream. At the 2013 Ohio Pawpaw Festival, I had pawpaw beer. It was decent. In 2021, the Keepsake Cidery made a batch of pawpaw cider. I liked it, but that particular batch didn’t age well. I’ve heard of people making jam with it, but my take is that they are best eaten raw and chilled.
Pawpaws only keep for a few days after picking (after which they turn brown, mushy, and cloyingly sweet). For me they are an ephemeral late September or early October pleasure.
Future Work
By 2012 I had just the one (as of August) ten-foot tree producing fruit. I had another five-foot tree that suffered around eight inches of winter dieback. I had three more plants that died down to within a foot of the ground but that put on three to four feet of growth over the summer. That’s all that remained of the fifteen to twenty-some-odd plants I had previously put into the ground, starting in 2003.
In late summer 2013 my son and I attended the Ohio Pawpaw Festival. We participated in a tasting contest in which the judges sampled various fruits but then let the audience try them as well. We felt our best fruit back home was at least as good as the contest winner that year. We took away several dozen seeds from the festival, from several high-scoring entries, and I propagated a few. Two specimens survive from that effort, and one of these produces large, good-tasting fruit. They are about eight feet tall now.
Since 2012, I have been pollinating pawpaws by hand and saving seeds, using the process outlined earlier. I have three favorite trees that produce especially large, delicious fruit with just one row of seeds (some specimens have two rows).
As of 2023 now, I have raised multiple generations of plants and passed on hundreds of seedlings to other northern gardeners.
Nearly all specimens in my yard tolerate our winters well, because, as discussed earlier, I try to remove the ones that don’t. I agonize some over whether to keep plants with otherwise desirable traits that lose branches in heavy winds or under heavy fruit loads. I have a few of those trees on probation. Their fruit quality is just too good.
Some other trees produce smallish fruit later on in the season, and for me, this is a particularly undesirable combination. I only keep those trees, and trees producing fruit with a double row of seeds, if they are particularly strong or hardy. I save seed from them, but I do not pollinate using their flowers.
Some of my trees now overtop the lower eves of my house, and passersby occasionally approach me and ask what the large-leaved, exotic-looking trees in my yard are.
There is still room for more growth and a few more trees, and my story is not yet over. I’ve gained enough experience now, though, to at least offer fellow aficionados in USDA zone 4b some ideas about how to start, and, I hope, something for them to build on.
