Update, July 2023: Near as I can tell, none of these saved seeds germinated. So this ended up being a lot of work for nothing. This fall, I’m going to try something easier, such as tossing whole fruit into pots of soil and seeing what comes up the next year.
I have a couple of pawpaw trees in my back yard. Well, two big ones, pictured above. And then what amounts to a growing pawpaw patch all around them.
Near as I can reconstruct from old emails, these were planted in the spring of 2009, and they are:
- Stark Brothers Mango Grafted Pawpaw. This is a large-fruited, late-ripening variety with particularly tasty fruit. Here’s their ad.
- Edible Landscaping Select Pawpaw. This is just a normal, native-to-Virginia pawpaw, that the folks at Edible Landscaping selected for better-than-average fruit. This is a small-fruited, early-ripening variety. Here’s their ad.
I have, on occasion, eaten some of the Mango Grafted pawpaws, and they are delicious. I no longer eat pawpaws, though — see Post G24.
Propagating pawpaws
I’ve now been asked to supply some fruit to people who want to try growing pawpaws.
I naively said, sure, I’ll just pick up some of the remains of the rotting fruit that are still on the ground. I figured, seeds are tough, a seed is a seed. Just pick them up, let them over-winter, and plant them next year. Give it some time, and you too can have a delicious Mango Pawpaw.
But, as is my habit, I decided to do a little research. And the answer is nope. Everything I just said is incorrect.
First, from the Home Orchard Education Center, I learned one key fact: Pawpaws do not grow true to seed. They are like apples in that regard. Plant a seed from a Granny Smith apple, and you’ll get an apple tree. But it’s not going to be a Granny Smith. Same with pawpaws, apparently.
In particular, seeds from that delicious Mango Grafted pawpaw are not going to produce Mango Grafted pawpaws. The only way I could get more of Mango Grafted pawpaws would be to .. wait for it … graft a cutting from that tree onto some pawpaw rootstock. Which, I now realize is probably why grafted is part of the name. (Duh.)
Second, there’s a recommended process for saving the seeds. Apparently the seeds are fairly fragile, and require significant special treatment. (Which, to be honest, does not quite square with the dozens and dozens of little pawpaw trees I mowed down this year. Fragile or not, mine seem to be quite happy to sprout after falling on the ground and overwintering there.)
I’ve now started looking into what you’re supposed to do to save pawpaw seeds. And there’s quite a bit more to it than than just picking them out of some old rotted fruit and chucking them in a paper bag until next year.
By far the most surprising recommendation is that you’re supposed to keep the seeds moist. That’s a new on on me. Decades of growing stuff, and the advice has always been the opposite: Keep saved seeds dry. But for this one, nope, you have to keep it moist. “If seeds are dried for 3 days at room temperature, the germination percentage can drop to less than 20%.” (From Peterson’s Pawpaws).
That makes any that I gathered from truly well-rotted fruit suspect. They weren’t exactly dry, as we’ve gotten a fair bit of rain in the past few weeks. But they aren’t guaranteed to be moist, as would be the case for seeds from intact fruit.
Separately, you have to chill them. Commonly, they spend the winter in your fridge, inside something that will keep them moist. I see recommendations of keeping them on damp paper towels, moist sand/peat moss mix, moist sphagnum moss, moist potting mix, or some similar sterile medium. Inside a zip-lock bag seems to be the most common technique.
But you can also plant them outside, keep their planted area moist, and let the winter chill them for you.
Third, the common recommendation is to remove all traces of pulp and membrane from the seeds. Apparently, there’s something in the pulp that inhibits growth.
Finally, if you plant in containers, for eventual transplanting into the ground, those containers need to be deep, as these produce a long and fragile taproot. That much I already knew as these are reputed to be almost impossible to transplant out of the ground. I’ll be using my paper bag technique from Post G22-012.
References also say that a) the seeds need high (75F to 85F) temperatures to germinate, one source specifies a soil temperature of 70F to 75F, b) they typically take a month to germinate in any case, C) they can do with a 24-hour warm water soak to speed germination, and d) you don’t get much foliage for the first couple of years. All told, this seems like a project for somebody with more patience than I have.
One source — and only one source — says that wild pawpaw seeds need to be planted in soil taken from around the parent tree. Something about microbes. Not sure I believe that one. That same source — and only that source — says to store them inside in a paper bag for a couple of months, then moisten and refrigerate.
References vary on whether or not you can freeze them. Some say yes, some say absolutely not. I am dead sure that these would freeze over the winter, naturally, so I find it hard to believe that freezing them would kill them.
Finally, the “float test” to separate viable and non-viable seeds does not appear to work on pawpaws (reference). Which, to me, goes hand-in-hand with having to keep them moist. This is just not a normal seed.
In any case, here are a few internet references on what you are supposed to do.
The plan
At this point, given that I want to try this, my plan is to prep a large number of seeds for overwintering in the fridge, and give away bags of prepped seeds. If I do this again next year, I’ll know enough to collect the whole fruit before they rot, to ensure that the seeds do not dry out.
So, the plan is:
- Start with whole fruit where possible.
- Scrub the pulp and membrane off the seeds
- Give the seeds the recommended soak in dilute bleach solution.
- Bag them up in ziplock bags of moist potting soil.
Then they go into the fridge until next spring.
Edit: Addendum
These are now done and stored away in the fridge. All told, it took me maybe an hour and a half to process about 100 pawpaw seeds for storage over the winter.
I took the advice of several internet sites and “scrubbed” the seeds and pulp against a piece of hardware cloth, set over a bucket. This was the most time-consuming step, mostly because I didn’t quite grasp just how hard you had to scrub, to part the seed from the surrounding membrane. It went a lot faster once I decided to put more effort into it. And it was obvious when I had managed to get a seed out of its membrane jacket.
I soaked the mostly-clean seeds a few minutes, then cleaned off any remaining pulp one-by-one.
Five minutes in a weak bleach solution (10-to-1 dilution of standard laundry bleach), several rinses to remove the bleach, and the seeds got tossed into Ziplock bags filled with damp potting soil. And the bags got tossed into the back of the fridge.
The next challenge will be planting them in the spring. As I understand it, pawpaw seedlings really don’t like to be transplanted. They grow a long, fragile tap root before they even begin to break the surface of the soil.
Direct-sowing into the soil is preferred. But I’m planning to raise seedlings to give away in next spring. So I need to find or make some suitable containers.
You can find any number of very tall plant pots and containers specifically designed for growing tree seedlings. But it is far harder to find very tall biodegradable pots, so that you can plant the seedling without disturbing the plant roots. In particular, rumor has it that pawpaws can put out a one-foot tap root before you even see any leaves. So I was looking for slender biodegradable pots at least one foot tall.
The best of the bunch seemed to be the lightweight Zipset (r) plant bands, 14″ x 3″ (reference). These are more-or-less open-ended un-waxed lightweight milk cartons, and should degrade in less than a year. They seemed to have the exact right combination of size, stiffness, and biodegradability. They are cheap if bought in bulk, but the smallest quantity I could buy was a carton of 500. That was far too many.
Instead, I’m going with 17″ tall biodegradable fabric grow bags (reference). I can pick up 50 for $15. The big unknown there is whether or not they really will degrade once planted. I’ll bury a few this winter and dig them up before I decide whether or not to start my pawpaw seedlings in them.
In any case, at that price, the cost of the potting soil to fill them will far exceed the cost of the grow bags. So it’s not like the bags represent a big money gamble in the overall scheme of things. .
I decided against several varieties of home-made pots, just because I didn’t think they would be sturdy enough. I could, in theory, make a foot-tall paper pot, out of newspaper. Or use grocery bags, cut up and re-glued. Maybe wrapped with jute netting, for strength. And so on and so on.
But all of those seemed to be a risk, and none of them seemed to be worth the trouble when I appear to be able to buy usable containers for 30 cents apiece. After going to all this trouble, it didn’t seem very bright to take a gamble on the containers used to grow the seedlings.
So, tall grow bags it is. We’ll see how this all turns out, next spring.
