Ailanthus altissima (tree of heaven) – how can I get rid of it?

(Question)

Ailanthus altissima – “tree of heaven” is everywhere in my garden. There were 2 tall ones when I moved in, and no sign of trouble for 10 years, then in the last 6 years, they have begun sprouting up everywhere. No matter how much I try to dig out the roots, their network is enormous – everywhere. I dug up 50 small ones this year, and despite digging up many many before, there are 8 tall ones (16′ – 24′( in addition to the 2 original tall ones (50′).

I now know these are invasives, and they propagate both by seed and by rhizomes. I also know they release something into the soil which is a toxin to many other types of vegetation.

I want my backyard to be an edible garden. I understand glyphosate is my best bet for eradicating them, as it will enter the root system/network, although some people are skeptical about its safety.  I it contacts the soil directly, it becomes inert, but if it goes through the roots before contacting the soil, it can last 6 weeks, or in one study/claim from Sweden, 2 years.  Some say it harms microbial life of the soil. Still, it seems to be the best option. If I use glyphosate, will the food I grow the following year or the year after be safe to eat?  Someone suggested gasoline; sounds crazy to me, is it safe?

(Answer)

You are right, the “tree of heaven” is not so heavenly – it’s an invasive pest.  In Ontario, glyphosate is not permitted to be used for cosmetic purposes in home gardens.  Ontario’s Pesticide Classes and Database provides details.  For example, glyphosate-containing products cannot be used just to get rid of weeds, but can be used on home gardens in certain situations, such as to control plants that are poisonous to touch and are a risk to public health and safety (Class 10 pesticides).

Use of a toxic, flammable agent like gasoline is never recommended in gardens.  As well, pouring gasoline over your weeds could result in your being reported to the Ministry of the Environment, as this would be considered a “spill” under the Environmental Protection Actas well, gasoline could seep through soil into the groundwater.

For successful removal of Ailanthus, you must kill the roots and prevent additional sprouting. Your best option to get rid of this pest is to dig up or pull the young seedlings, as you have been doing.  Be sure to remove the entire plant – this includes all roots and fragments, as you don’t want the plant to regrow.  It will take persistence to remove root suckers and the thriving network of lateral roots.  Make a note where the seedlings were located and follow up the next season to make sure they’re not sprouting up again.

As well, target female trees and gather their seeds to help reduce spread of the pesky plant.  Dispose of the seeds and all plant parts via your city’s recycling system – don’t compost them.

Cutting mature trees is not productive, as this produces stump sprouts and more root suckers.  However, for the larger trees, you likely have no other choice.  You may want to call in tree removal experts; they could cut down the trees, attack the stumps and remove the root system – but they may have to return for a couple of seasons. Regardless of size, it’s best to cut the Ailanthus in the early summer to “hit” it when its root reserves are at their lowest.

You may find the following link helpful: Plant Conservation Alliance’s Alien Plant Working Group – Fact Sheet: Tree of heaven (2009)