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My neighbors have a great tall Ailanthus (Tree of Heaven). Apparently, before I moved into my house, so did our yard. We now have an enormous stump and a bazillion new shoots that come up from hidden roots all over the back portion of our yard. I call it my "weed tree", because no matter how often I try to pull out new branches, next week I'll find six new three foot high trees popped up. I don't think I can remove the stump without machinery, and I'm not even sure what machinery to use.

Making matters worse, it's on a hill-side which is steep enough to make my working on it a pain in the neck, and potentially dangerous. Eventually I plan to terrace and cultivate this hill, but that won't be possible as long as the Ailanthus is still there.

Should I just give up and hire a landscaper to rip up the stump and the entire portion of the yard that's apparently a dense network of Ailanthus roots? Presumably that would make the terrace work easier for me as well. Or is there some (cheaper) way to prevent it from growing? Although my garden and yard care is entirely organic, I might be open to a chemical warfare approach only if it could be targeted to just the weed tree.

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    I can't see any amount of effort being worth anything as long as your neighbors keep their tree, which will presumably continue sending runners into your property. – bstpierre Jun 14 '11 at 1:22
  • @nicholas a. evans, have you tackled this challenging issue yet? If yes, how did you tackle it? If no, are you open to hearing other methods? – Mike Perry Aug 31 '11 at 17:03
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I would suggest sheet mulching, but it sounds like this tree is too aggressive for it. The wiki article says the roots can damage sewer and drainage pipes. Yikes! It does say that it doesn't tolerate shade well. So one thing you could try is a very thick sheet mulch -- like several layers of thick over lapping cardboard -- on top of which you could plant a temporary layer of fast, densely growing plants that will produce heavy shade over the top of the mulch. Assuming you can get a hold of that much cardboard/hay/organic matter and that it doesn't all just slide away down the hill it might work. But it's probably a long shot and that's a fair bit of work. Upshot, no chemicals and improved soil as a bonus ;)

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How long have you been fighting it? If it hasn't been two years, just keep at it. If more, and it hasn't slowed down, consider either/or:

  • Don't cut the new shoots, just use Roundup on the leaves. I think the Roundup will get back into the stump - I'm not sure, though. If you are careful with overspray, etc., the Roundup won't affect much else.

  • Bore 1" holes in the top of the stump and pour stump remover, aka saltpeter, aka potassium nitrate, in to kill the stump. Caution: this will over-fertilize the nearby soil, burning other plants. Try to minimize the amount that gets out of the stump. This has the advantage that it will accelerate rotting of the stump. This usually takes a year or more to work, but I think it will be relatively fast with Ailanthus because the wood's so punky.

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Ailanthus is also invasive in my region (Pennsylvania). Once it has a strong root structure (as in your situation) the only way to eradicate it is to kill the root system. Glyphosate (e.g., Roundup) on leaves can be effective on small roots, and if you persistently soak shoots you might eliminate it after a few years.

However the now preferred method for dealing with a hardy ailanthus infestation is "basal application" of triclopyr in a 5% concentration with a miscible oil (diesel is used most commonly): Thoroughly spray the circumference of any growing wood from the ground up to 15". This will carry the triclopyr into the root system where it can kill within a few weeks. (Although if you only have small shoots from large roots, it may take multiple applications to get enough of the herbicide into the roots to kill them.) If you aren't careless with overspray this will not affect any surrounding plants.

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