On our 11000 square feet backyard, we have 6 trees. One of them is a huge, majestic balsam poplar, about 60 feet tall. Next to it, not very far, are 5 other poplars, but not of the balsam variety. They are much younger since we remember well 8 years ago, when we moved in this house, their trunk were maximum 5 inches thick. Now they are 15 inches thick.
Up until now, we had our vegetable garden as far as it could be from those trees, simply because we chose, logically, to set it up where there was maximum sunlight.
But last fall, we decided to set-up an other growing area (400 square feet) for vegetables which would be content with the 8 hours sunlight under the high canopy of our huge balsam poplar tree.
Last september we double dug, we removed as much rocks as possible while doing so, we amended with compost and aged horse manure... And it paid, we know it paid because when I dug holes to transplant vegies this spring, the soil (originaly clay) was crumbly and loamy and chockfull of worms.
And guess what... Nothing does well there, despite our diligent efforts in preparing the beds. Peas are 3 inches tall since March, they didn't grow more than that, they refuse to flower. Fava beans plants are barely at knees' length (and I'm not tall, only 5'4") when they usually grow to my shoulders' length. They look sickly and sport with obvious fatigue few seldom flowers. Broccoli and cauliflowers grew maybe half an inch, if even that, since the first week of May when I transplanted them there. The coriander I direct seeded did actually germinate, but is stalled at the second set of leaves since 3 weeks.
It bugged me no end that we had such bad results in those new beds. We worked so hard to prepare everything. After eliminating all the obvious causes why vegetables would stall their growth and wither slowly at almost infant size, I had the idea to research if the trees had anything to do with it, since I read at more than an occasion some trees are allelopathic. And that was it. Balsam poplar is allelopathic.
And it doesn't stop there... Usually, I acclimate all my seedlings on the deck facing west before transplanting in the garden. We have a door to the garden right off of the basement were I start my seeds at the end winter and very early spring. I never used it because that was the door our Great Pyr dog used to go out in the garden, and I would have asked for trouble if I dared put seedlings out near that door. He would have left nothing to plant, even the trays would have been chewed with energy and passion. But our dog passed away, and this year, for the 1st time in 8 years, I did use that door, because it's closer, more convenient and lower stairs to go up hands filled with seedling trays. And you know what? Our huge tree offered a great dappled, light shade, perfect for seedlings acclimatation. I did put them there, under the tree. Sigh....
So after a full 8 days of progressively letting the seedlings under the trees longer and longer each day, I transplanted them in the full-sun, older vegetable patch. It's a 700 square feet garden patch and the seedlings are galore. 25 tomato plants, 30 hot and sweet peppers, a ton of celery, 7 different kinds of lettuces and so on, and so on... They've been transplanted 2 weeks ago. They definetly seem stalled, almost all of them. For some it's too soon to tell since they are slow-growing to begin with (leeks, celery...) For others, like tomatoes or peppers, they definetly show signs of great weakness. The cucumbers all died, I didn't have time to even transplant them in the garden, they died right under the tree while I was acclimating them. At that moment, I didn't realise the tree was poisonning the seedlings, I thought they got a virus or something.
Anyway, now I'm asking you, is my whole work down the drain since all the seedling went under the tree? Will the plants recover now that they are in their permanent location far away from it? What can I do? How can I work around all those 6 allelopathic trees in my backyard now that we definetly need to expand our growing area to increase our food independance?
Just to spare you questions, no, there is no way we will cut the huge, old, beloved balsam poplar. It would be like putting to sleep a pet because he is becoming bad-tempered or troublesome. We love that tree.
Yes, we thought cutting down the other 5 younger poplars and replacing them with fruit trees. But there is a big problem with that, our town forbids cutting trees, unless they're sick or represent a danger to houses (or people of course). May be there will be a way to obtain an exceptionnal permit to cut them down though, because one neighbout obtained a permet to cut down his giant "Christmas" fir in order to make room for a swimming pool they installed 2 weeks ago. So if we negociate and say we will replace the 5 of them allelopathic trees with non-allelopathic ones, reminding them how a swimming pool is so futile compare to food security... I don't know... I'm tired just thinking of the ordeal.
Your ideas, knowledge on the subject of allelopathy and suggestions are more than welcome,