Growing paw paws in Pacific Northwest

I am interested in advice on several aspects of paw paw cultivation.

(1) Producing paw paw fruit. I live on a small island off Vancouver Island on the west coast of Canada. The winters here are mild (usually rainy from October through April with temperatures dipping to just above freezing, with 1-3 weeks of snow and freezing temperatures) so I am not concerned about winter survival, but summers are cool and I'm not sure there is enough heat to reliably ripen the fruit.  The summers here are long, dry, and sunny, but daytime temperatures are often only about 20-25 C (about 70 F) with maybe a week getting up closer to 30 C (about 80 F).

I know that at least one fruit aficionado on Vancouver Island has them successfully fruiting in his backyard garden (Bob Duncan of Fruit Trees and More) but he has them espaliered against a south-facing wall in an intensive fruit tree situation. I am hoping to produce fruit with paw paws planted in the understory under sweet chestnuts, similar to the mixed chestnut and paw paw setup that they are using at Red Fern Farm in Iowa. However, I am concerned that the shading effect of the chestnuts might reduce the heat units to the paw paws even more. In their native habitat they do well in shade, but it is a heck of a lot warmer in summer there. Do they need a minimum temperature to ripen, or a certain cumulative number of heat units?

(2) Overwintering very young seedlings. I bought seeds from England's Orchard in Kentucky last spring and asked for the shortest-season seeds they had. So far I have about a dozen that have germinated and are growing outside in pots. They are pretty small, only a few inches tall and with about 4-6 leaves. I am not sure whether I should leave them out in pots for the winter, perhaps in my unheated 'greenhouse' (it's one of those semi-opaque garage shelters that I use for tomatoes and other plants that need more heat or extended season), versus bringing them into a cool room in the house. I wonder if the latter would be safer, and maybe even allow them to grow a bit more over the winter. So far they have not dropped any leaves for the winter and it is about 7-10 C out there (45-50 F).

(3) Seed germination. More than half of the seeds I planted this past spring/early summer did not germinate this year. I'm guessing maybe a 20% germination rate? They were stratified by the grower so in theory should have been ready to sprout when I got them. Someone at the NNGA/NAFEX meeting suggested that they might need warmer germination temperatures than what I had here (I had them in the warmest microclimate available outside, but see note above about summer temperatures). Should I leave the unsprouted pots outside overwinter for another winter of stratification in hopes of some sprouting next year, or if they have not already sprouted are they basically done? I don't think they dried out at any time, not sure what the normal germination rate might be or how long the seeds might last following planting. Another option would be to bring them into the warmest spot in the house, which would be near the wood stove, in hopes of getting enough heat for a successful late germination of the non-starters.

Thanks in advice for any insights or suggestions. - Andrea

Andrea Locke wrote:I am interested in advice on several aspects of paw paw cultivation.

(1) Producing paw paw fruit. I live on a small island off Vancouver Island on the west coast of Canada. The winters here are mild (usually rainy from October through April with temperatures dipping to just above freezing, with 1-3 weeks of snow and freezing temperatures) so I am not concerned about winter survival, but summers are cool and I'm not sure there is enough heat to reliably ripen the fruit.  The summers here are long, dry, and sunny, but daytime temperatures are often only about 20-25 C (about 70 F) with maybe a week getting up closer to 30 C (about 80 F).

I know that at least one fruit aficionado on Vancouver Island has them successfully fruiting in his backyard garden (Bob Duncan of Fruit Trees and More) but he has them espaliered against a south-facing wall in an intensive fruit tree situation. I am hoping to produce fruit with paw paws planted in the understory under sweet chestnuts, similar to the mixed chestnut and paw paw setup that they are using at Red Fern Farm in Iowa. However, I am concerned that the shading effect of the chestnuts might reduce the heat units to the paw paws even more. In their native habitat they do well in shade, but it is a heck of a lot warmer in summer there. Do they need a minimum temperature to ripen, or a certain cumulative number of heat units?

(2) Overwintering very young seedlings. I bought seeds from England's Orchard in Kentucky last spring and asked for the shortest-season seeds they had. So far I have about a dozen that have germinated and are growing outside in pots. They are pretty small, only a few inches tall and with about 4-6 leaves. I am not sure whether I should leave them out in pots for the winter, perhaps in my unheated 'greenhouse' (it's one of those semi-opaque garage shelters that I use for tomatoes and other plants that need more heat or extended season), versus bringing them into a cool room in the house. I wonder if the latter would be safer, and maybe even allow them to grow a bit more over the winter. So far they have not dropped any leaves for the winter and it is about 7-10 C out there (45-50 F).

(3) Seed germination. More than half of the seeds I planted this past spring/early summer did not germinate this year. I'm guessing maybe a 20% germination rate? They were stratified by the grower so in theory should have been ready to sprout when I got them. Someone at the NNGA/NAFEX meeting suggested that they might need warmer germination temperatures than what I had here (I had them in the warmest microclimate available outside, but see note above about summer temperatures). Should I leave the unsprouted pots outside overwinter for another winter of stratification in hopes of some sprouting next year, or if they have not already sprouted are they basically done? I don't think they dried out at any time, not sure what the normal germination rate might be or how long the seeds might last following planting. Another option would be to bring them into the warmest spot in the house, which would be near the wood stove, in hopes of getting enough heat for a successful late germination of the non-starters.

Thanks in advice for any insights or suggestions. - Andrea

In your neck of the woods the warmest micro climate you have or can create combined with the most adapted seed genetics are going to be your best bet. I would keep them in full sun if you have extra rock, surround the trees, and if possible create a south facing horse shoe micro climate. I would get seeds from Bobs earliest producers vs seed from Kentucky and/or grafted cultivars. On the paw paws extended growing range it’s all about the regional seedling genetics, which will keep adapting.

I would not over winter paw paws outside anywhere it touches freezing. The fleshy paw paw root will die if frozen in pots. In the unheated greenhouse sounds fine but I would heavily mulch around the pots- here in our cold midatlantic winters I create a square of strawbales then which I put all my potted paw paws inside and cover with wood chips for the winter, an unheated garage will work as well- but they do need dormancy.

Properly handled paw paw seed can be in the 90% range for germination, moisture and cold for 90 days I germinate my seeds on a heated seed mat or at indoor room temps. I detail my process well in my book.
Maybe we’ll come visit you one day, we love your part of the world.

I’m thinking it might be Bob, that I read uses seaweed to heavily mulch his paw paws...

Michael, thanks for that advice.

It will certainly touch freezing here, reliably getting down to -5 to -10 C every winter and occasionally as cold as -20 C.  And with no consistent snow cover to protect little seedling plants. So I definitely won't leave them out in the open. Sounds like the unheated greenhouse is the right environment, well insulated with bales. I don't have any wood chips handy so I will surround them with bales and bury them well with leaves. If I were to bring them indoors to the cool room for the winter I suspect they would not be cool enough for dormancy. Although that led me to wonder, is winter dormancy required for survival/growth of the young seedlings or would that be more of a requirement for fruiting?

I don't think the paw paws that Bob Duncan is growing are local, they are brought in from somewhere (out east?). I may check with him about possibly getting some seeds. At the very least it would mean these are seeds from a plant that definitely produced fruit under our conditions, even if I am not getting 'local' genetics as such.

I am not getting anything like 90% germination, that's for sure! I did find an older paw paw thread somewhere on permies that mentioned it is not unusual for these seed to take 2 years to germinate. Do you think it would be better to leave my existing planted ungerminated pots outside in the bale-insulated area with the seedlings for the winter in hopes of simulating natural stratification again, or should I bring them indoors and give them some heat in hopes of getting them to germinate indoors over the winter? Given that England's Orchard are experienced paw paw growers and sell their seed already stratified, I think it is probably safe to assume the seeds were appropriately stratified during their first winter before I got them. I'm actually thinking maybe the smart thing to do would be to leave half out in the insulated area with the seedlings and bring the rest in to see if some warmth will wake them up...

And I forgot to address your comment about using seaweed as mulch for paw paws. I have found that seaweed makes excellent mulch for everything! I used seaweed and eelgrass cast up on the beach for 20 years on the east coast of Canada and here for the past 7 years as well. Loaded with micronutrients and adds lots of organic matter.

i grow pawpaw in pots in PNW they fruited for me.
for seedling that size you are describing as mention shoulf be brought inside the first few years. under 3 year old should be indoors. as well as in partial shade and not in full sun the they sensative to sunburn. the chill requirment is for fruiting. i think you can try growing your pawpaws in large pots to test and trail to see if they do well under the large trees you mention. there will be a difference in when they ripen when under partial sun rather than full sun. here this summer fall has been cool and my pawpaw ripen in late october. with better summer it should ripen early october. i would make sure they ripen in a good timeframe before planting in ground. once planted they dont like to be transfers their tap roots are sensative to transplanting.

I have been growing pawpaws here in PNW for about 20 years. I have grown many from seed.  We get more heat in Portland than you would on a Canadian island, but I still think in full sun it should be fine.  The cold here is not much of an issue. We don't get very cold.  A bigger issue is making sure they get water in the summer. I've had leaf burn.  Full sun is key.  There are no local native pollinators, so if you want a lot of fruit, hand pollination is advised. Then you can get a LOT of fruit.
John S
PDX OR