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I've been looking at the root pruning pots and wanted to experiment with them this year. I've seen people on YouTube using A cloth like root pruning bag and they'll set it in a kiddy pool of water. They just keep the water topped up and the pots wick up what they need.

My question was, when the roots grow down to where the water level is, will the root tips die and cause back branching on the root the same way it does when exposed to air?

I can see it going either way. I could see the plant knowing it and grow into water and killing the tip that's touching it, causing the roots to back branch. I can also see it rotting and allowing bacteria in. Obviously, plants can be grown this way, because plenty of plants (non-water plants) grow beside water and there are the YouTube videos where they get better than expected results, but does it prune the roots and would it be healthy for the plant in the long run, like if you were trying to start trees from seeds or cuttings and were worried about them drying out.

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This is my kiddie pool sub irrigation planter with a couple of dismal looking tomato plants, and one bag with 4 corn and one Apple tree seedling. I probably over did it! Two of the corn look very weak.

What I've observed, apart from the mosquitoes breeding in the water, is that the roots grow into the water which is well oxygenated. So, they don't prune unless you let the pool dry out, and then they die back.

Because it's sitting in water mostly I would expect the roots to circle at the bottom. So, I wouldn't use this method to prepare trees for transplanting.

A standard root pruning pot, such as the air pot, has a gap at the bottom to prune the bottom roots. And they pretty much stress that you need to drip irrigate them since they dry out so quickly.

So, in summary, using air permeable bags made from recycled PET bottles ( preferably from ones known to have low lead levels ) is good for growing plants for final use, but I doubt that they'll be as good for transplanting as a proper air pruning pot.

kiddie pool planter

Edit: this is the corn cob from the above plant after microwaving. Surprisingly all the kernels are fertilised even though it's the tallest plant of 4 from one grow bag. It appears foreshortened due to the angle the picture was taken.

kiddie pool corn cob

  • Thanks graham. Assuming I'm not talking about a long term plant like a tree, but a short term plant like you're corn or tomatoes, have you had success with this method in the past? I figure with a shorter lived plant like that, it might not mater that the bottom roots aren't being 'pruned', since the top ones will be. – Dalton Mar 11 '16 at 13:37
  • This is the first year I tried it. I just used bags I had lying around but have since got some Walmart bags that are much stronger I'm told. It worked very well initially but you need to have to stabilize the plants to stop them blowing over in the wind, and a way to support things like tomatoes. Also I didn't feed them as I should. Need to also use potting mix, and a way to suppress mosquitoes. – Graham Chiu Mar 11 '16 at 16:09
  • I was thinking about the mosquito thing. I was trying to think of things that wouldn't hurt my plants, or me if I was going to be eating them, but be harmful to mosquitos. My first thought was gold fish, because they eat mosquito larvae. You'd probably have to supplement their feed and even a full kiddy pool isn't likely to be deep enough. It'd heat up and kill them. You might get a fish poo benefit to your plant though. Another thought is that the larvae apparently take 2 weeks to develop. You could either flush it or dump it every week to kill them. Lastly, you could build a bat box. – Dalton Mar 11 '16 at 19:03
  • Oh, you might also be able to put just a little water in the bottom. You'd have to add it more regularly, but if it completely drained, then the larvae would die. I know they dont' need much depth though. I have a Venus Fly Trap sitting in a tray with about a .5-1" of water and they'll breed in that. I just dump it out on a regular basis. – Dalton Mar 11 '16 at 19:05
  • The recommendation is to drill an overflow hole at 2 inches, and then fill with pebbles to above the overflow line. This is supposed to stop the mosquitoes but I didn't bother. – Graham Chiu Mar 11 '16 at 19:31

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