anyone tried growing a tree or berry bush in a pot with the bottom knocked out? I was thinking of trying this for the berry bushes I recently bought (blueberry, raspberry and goji) because it will allow me to run hardware cloth under the pot to protect the plant from gophers and voles; while at the same time allowing the berries to send some roots down deeper into the ground when they get larger. I read that goji berries simply stop growing once they reach the bottom of the pot you put them in - not sure if it’s the same for blueberries and raspberries. But the bottomless pot or 2x2 planter seems like it would solve that problem, and also eliminate the need for future repotting.
One thing I’m wondering is if one does this, can one still use a mix that is best for containers and have things turn out well, or is it better to use a medium that is primarily native topsoil, since the plants are eventually going to end up putting roots into the ground? I have hard clay soil so I imagine it will be a bit of a shock for the plants as their roots travel through a well aerated and well draining mix to suddenly hit the clay beneath, but maybe by that point they would be mature and tough enough to dig in?
I often leave young potted trees sitting in the same place all winter and by spring when I go to move them they will usually have begun to send roots into the soil below. I have clay soil too and I notice that in especially compacted areas plants will spend a lot of time sending roots around the thin, damp airspace between the bottom of the pot and the soil before finally growing downward. They do always, given time, grow into the ground in my experience.
Once, when I was doing some gardening for someone who had a couple of potted linden trees she had purchased a number of years before, I went to move the pots and found them completely attached to the ground. I was surprised because the trees were tiny—they looked like newly purchased 2 gallon plants, but they had developed roots the exact width (1-2”) of the drainage holes. I had to rip them out of the ground, leaving behind most of the root system, in order to replant them. Last time I saw them, five years later, they had grown into healthy looking shrubs but were still under 5’ tall—so I guess they’ve been somewhat stunted ever since. I’ve actually heard of people doing this intentionally with fig trees in order to keep them potted but allow extra root development in the summer, but I don’t know how well it works.
Also, the only exception to this I’ve experienced was with a blueberry. I left the pot on the ground and its roots never spread outside the pot. I planted it a few months later, but even now, six years later, it’s half the size of the blueberries beside it that went in at the same time. I think this was more due to not watering enough and then planting in summer, though.
I think it’s a bit different with a wider container that has the bottom knocked out. It’s more like a small raised bed. Still, a few concerns I would have are:
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A lot of plants grow wide, shallow feeder roots and use deeper roots more for anchoring and water access. I think this why those lindens were stunted—most of their nutrition came from a small area of old potting soil. This might not be a problem for small plants like berries but I would avoid trying anything larger this way. The hardware cloth would obviously also interfere with roots if you did trees this way. I think using a very wide, shallow pot would be your best chance for success.
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Raspberries spread by underground runners, usually a greater distance than 2 feet. If they can contact the ground they’ll ignore the pot and you’ll end up with raspberries outside of the containers, but maybe this is a plus. Over time, they’ll probably prefer the wetter, higher nutrition clay and not send as many shoots through the potted area.
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Containers can become hot and dry in sunny weather which means extra maintenance. Additionally, a lot of plants (this does vary by species though) will adapt the position of their root zone over time to wherever the ideal balance of moisture and air is. If you have a very light mix that dries out and stays dry for several weeks the roots in the upper part of the pot will die off, essentially lowering the root zone underground. If the mix then becomes flooded for an extended period of time it could suffocate the plant. (Or, in the case of a raspberry, it might send new shoots up far below ground when dry, then get smothered when wet).
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If you ever want to move the plants they will have roots intertwined with hardware cloth, which will make it impossible to dig them out properly.
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thanks for going into such depth in your reply - very helpful!
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