Greenhouse pawpaw seedlings

I read a while back that pawpaw seedlings can grow inside a greenhouse. I have read before many times that they must not receive direct sun as seedlings, so I decided to test several this spring. The seedlings in the greenhouse are about 3 weeks of growth ahead of the ones outdoors in morning only sun.
So they seem to do very well in the geeenhouse even in full all day sun!
My question for those with experience is this; Does growing in full greenhouse sun harden the plant for planting outdoors in full sun next spring? Please advise if you have tried this, and your results
Kent, wa

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Does your greenhouse have UV treated walls?That probably helps and yes,I’ve been successful at growing them in mine.Smalls slugs seem to like eating the leaves.

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Too early in the year to assume success in the greenhouse. If they still look good by October, then you succeeded.

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I’ve had trouble with new grafts on pawpaws surviving in close to full day sun, so their tolerance for full sun isn’t great at certain stages of growth. But I’ve also had seedlings come up in a relatively sunny area in my front garden and seem as happy as can be. They are just from seeds I tossed in the garden while eating pawpaws on my front steps. One is on its second leaf and is almost 2 feet tall.

Pawpaws are weird…


Hi Brady
Yes, although it’s fairly old about 29 years, it’s polycarbonate walls were advertised to be 98%UV shielding, so that must be the secret to full sun toleration. These seedlings were grown in shade the first growing season of 2021. I observe daily to watch for signs of distress in the top leaves.

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I’ve noticed this on my outside pawpaws, too, especially once the dry season hits and the lawn and weeds turn brown. It is funny that slugs are basically my worst greenhouse pest, somehow I didn’t think about that before I had one. I go in there every night and pick baby slugs off almost everything in there.

Same here, I patrol both outdoors and the greenhouse for slugs. Found some on clover patch near one of my 2 year old Susquehanna, they love to eat the top tender leaves and can easily kill one! So this time of year I am on patrol 4-5 times weekly usually at night, especially on rainy nights

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After the first summer, they’re more apt to survive in sun the second year, but some don’t.

That is a different topic, but it’d be interesting to check genetics for a few that might survive in full sun as ‘volunteer’ seedlings. But, I’ve noticed they get enough shade under briars or weeds to sprout and survive…and are often fine in sun the secon year.

Hi Everyone:

Here in 4b (Canada) I must grow pawpaws in my greenhouse (not UV treated) for 3 years before I plant them. I receive plugs from nurseries, put them for 3 seasons in the GH and then they spend winter in my heated shed at 5 C. Up to now this strategy has worked just fine for me.

Putting pawpaws plugs in my GH makes them to grow astonishingly rapidly but it’s the same with everything I put in the GH. Some examples:


Hi Marc,
Thanks for your information. So I understand that somehow you grow them from cuttings. What is your process for doing this? I assume you are using dormant cuttings if coming from a nursery? Your information still leaves me wondering why a GH allows them to grow in full sun those first years since yours is not UV shielded. It just may remain a mystery. I am encouraged though to learn this can accelerate growth as I see it happening here.
Kent, wa

I think the most likely answer is some combination of the light diffusion (polycarbonate especially diffuses the light a lot) and reduction in intensity (most greenhouse glazing only allows 80-90% of light through). So even “full sun” without UV treatment is nowhere near the same intensity of direct sun outside. Maybe an untreated glass greenhouse would have similar properties to direct sun, since it doesn’t diffuse the light as much.

For example, I’ve noticed that seedling avocados have zero problems in “full sun” in my greenhouse, but they get badly sunburned if I move those same seedlings to “full sun” outside without slowly acclimating them.


Here’s the spec chart for the “Sunlite” polycarbonate panels, what my greenhouse uses:

Mine uses the clear 8mm twin wall, so that’s only 80% transmission, plus the diffusion.

Hi Dennis:

No, I do not grow them from cuttings. I receive them as tiny plugs from a nursery, put them in the GH for 2/3 years before planting them outside. With those photos I believe you will understand the process.

This photo was taken May 12, 2021.

This one was taken November 2, 2021


On April 28, 2022 Number 1 through 6 were then put into the ground in my orchard and the rest continues to grow in my GH because I don’t find them strong enough to plant them now.

From the last 4 photos published together you can see on the first one the last year pawpaws getting bigger. Unfortunately many trees are mixed up together. Mainly persimmons, medlars. Maybe you can differentiate all of them and spot the pawpaws.




Are those last 2 medlars? I’ve never seen the plants and they are very pretty!
( I’m thinking/ dreaming about what I want for our new place, when/if we get it, and medlars are on the “maybe” list. )

I’m around 43.5°N and I grow all of my pawpaw seedlings out in full sun and have never had a problem (yet) with them getting scorched. They’re all being grown out in tree pots though so they’re getting a good long tap root. The key is obviously to keep them moist, but well drained. I also wrap the pot tray in reflectix insulation to keep the sun from directly heating up the pots. It’s worked well for me.


@Viridian : the red arrows point to the 2 medlars. Marc


I think you will find that all greenhouse coverings that last multiple years block UV. If the covering didn’t have UV blockers in the outer coatings it would quickly degrade just like untreated poly does. The poly I have now has an inside and an outside. The outside has the UV blocker. Put it on upside down and it degrades quickly.

My greenhouse is about 50% light level compared to outside. And it’s very diffused light. I don’t think it’s the lack of UV that makes a greenhouse milder on plants. It’s the lower light level and diffused light.

Plants in my greenhouse use considerably less water than those outside. Less light and less wind.


Do modern double pane windows have UV protection and also diffuse sunlight?
I bring this up because,where I worked and had a small tunnel growing some vegetables,using painters poly,non treated.A coworker had some plants,that were kept inside,by the windows,until warmer weather came.
When it did,he put them in the tunnel and they all died.

It’s my understanding from another thread that discussed this (you’ll have to look around, might have been @don1357 talking about recycling?) that yes most modern windows do have UV protection.

Thanks Marc for responding, I am unfamiliar with the terminology “plug” but it looks like your process is very successful. Take care