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Invasive Trees in Colorado, Part I

A brief discussion on the merits of Ghetto Palm (Ailanthus altissima)

by Mike Wood

First, so we know what we’re talking about, see the Wikipedia entry on the ‘Tree of Heaven’ here.

This tree is considered to be an invasive species in Colorado, and no doubt in other places. Our fearless leaders have decreed it to be undesirable. There are no active eradication efforts to my knowledge. I will not discuss its demerits here, as those can be found in any official literature on invasives. Rather, I hope to demonstrate its utilities in the context of permaculture — pioneering, succession, land improvement, and ecological niches.

An interesting factoid I found in my research: one of these trees survived the Hiroshima A-bomb, 300 meters from where the bomb went off. It still lives today. Tough bugger. I have read much wailing and gnashing of teeth on forums about how difficult it is to kill. This is, in my opinion, a fact very much in its favor in the high desert steppe climate here, Colorado’s Front Range. It can gain a foothold nearly anywhere; I’ve observed it growing from minute cracks in sidewalks, hard, nearly-granitic sand, gravel beds, and highly salted areas near roadways — making it an ideal candidate for land reclamation.

It is one of the few tree species that will establish from seed in this climate. Most of what is sold in nurseries as ‘appropriate’ to the area requires careful nurturing to survive. Ailanthus needs no human intervention. A sprinkling of seed on the breeze will bring a forest in a few years’ time. Thus, it is quite useful for broadacre permaculture projects where windbreaks are needed, but where sapling, labor, and irrigation costs might be prohibitive. There is not, to my knowledge, a faster way to establish a windbreak than with a species that will easily grow 2-3 feet per year in its first few years.

Once the windbreak is established, other, more desirable species may be planted in its shelter. (Nothing is more pathetic than to see those poor little Western Red Cedars struggling against the cold winter and hot summer winds on the prairie. It is a climax species that grows under a canopy in its youth.) Once the desired climax species have grown, the Ailanthus can be cut for firewood and/or mulch; it will be easily controlled under a canopy. In fact, the chopping might be an ongoing process providing considerable useful organic material.

Ailanthus I have found mainly in the cities of the Front Range, from Fort Collins to Pueblo; most frequently in the more run-down areas where landscaping is neglected. It is an opportunist and pioneer, so look for it in places where it would seem to be in need. Seed hangs on the tree quite late. The optimum time to harvest seeds is late fall through mid-winter. See the Wiki page for a photograph of the seed clusters. They are easily stripped off in handfuls.

Here, a stand of Ailanthus altissima in a sun-scorched pile of gravel in an unmaintained industrial area. Irrigation is unlikely. Maybe 5 years old, at most.

Here, some more young trees, perhaps 3-4 years old, in a road ditch by a trailer park.

And a wider view. Except for the blue spruce and the pine, the rest of the tall stand is our friend. I’d put the tallest at perhaps 15 years; not more than 20. The trailer park is barely visible behind; perhaps the ‘ghetto palm’ moniker isn’t entirely inaccurate. Nevertheless, it’s shelter, habitat, and shade for a place where neither private property owners nor city officials will bother with landscaping, especially landscaping with a purpose.

I hope readers have found this informative. I’ll add chapters on more of my woody friends as time permits.


  1. Thanks for this post! We’re dealing with ‘tree of heaven’ in eastern Oklahoma, and appreciate this article and anything else you have time to share! I wonder if goats like to browse tree of heaven? I’ve heard it’s valued for medicinal purposes in Asia, but haven’t done the research yet.

  2. Very informative article, and in the right direction: Turn a problem into a solution. Find all the actual benefits this species provides in the web of life.
    Now, in view of the fact that this tree contains alleopathic (toxic to other plants) chemicals in the roots, bark,wood and leaves, it would be wise to do some tests before using it around fruit trees. Perhaps there are plants or trees that are tolerant of this trees’ toxins.
    Otherwise, the important thing is to find it’s proper ecological niche and use it’s “invasiveness”, resilience and fast growth in our favor: In very poor soils where nothing else grows anyway to prevent erosion and create habitat for wildlife, in abandoned landfills, in areas where “any forest” is better than “no forest”, such as areas in danger of desertification, or use it for firewood or making wood pellets, medicinal purposes, etc.

  3. Mike, next up…Eleagnus sp. (Russian Olive)? One of the toughest multi-purpose CO trees that people love to hate! Nice work!

  4. We call it Cancer Tree and it has taken over lots of the western US.
    At 5600′ in Bisbee Arizona, it is everywhere. It smells, has weak branches and will invade sewers and septic tanks. I would be hard pressed to ever plant it.

    1. REALLY? Everywhere? That is fascinating. I would of thought it couldn’t even survive in a climate like southern AZ, let alone thrive. I would imagine it would be a blessing in such a place for its shade and ability to create forests from a single specimen. How tall does it get? Whats its growth rate like? Can it fill open areas with little rainfall well? Could you perhaps post some pictures?

  5. Good job turning that problem into a solution! Seeing these pictures I instantly recognize the hardy sapling that grew in partial shade and in desert sand… definitely a strong pioneer.
    I have been wondering if there are any databases of similarly pioneering or remediative species. Does anyone know of anything like this? If you do, post a comment on this thread.

  6. Hi. Enjoyed the article. Anything that operates as a pioneering species should be celebrated for their hardiness and ability to shade the ground and build top soil. After all, that is their purpose. What is interesting is that I have noted a stand of these plants in Castlemaine, Central Victora, Australia and have wondered what plant they actually were. Perhaps it is time to collect some seed? Regards. Chris

  7. Familiar sight here in Germany as well.
    It used to be confined to the sheltered habitat of the inner cities – and was originally introduced to set up a silk industry – but in the current changing climate it’s expanding its habitat.

  8. This tree is a declared noxious weed in Australia. Don’t be an ecological vandal and spread this around, there are plenty of more useful species for you to propagate. Why would anyone want to plant a tree that smells of cat urine, is hard to eradicate,and is known to cause problems for people and existing ecosystem? Care for the Earth, care for the people…don’t plant noxious weeds.

  9. This tree it is a big issue to solve in the 4 centuries old Portuguese Coimbra´s Botanical Garden.
    I would understand the use of it to quickly recover forests after fire. Other great challenge in our country as in others.

  10. The problem is the solution. Exotics are here to stay….the challenge is creating, or allowing to happen, the recombinant ecosystems of the future. Anyone who cares to condemn a plant for being an invasive exotic should first take a good long look in a mirror.

  11. @Cathe: Not sure if serious, or troll. The term “cancer tree” is an oxymoron, and luckily for us they plant themselves, and don’t need your help.

  12. The problems (e.g. noxious weeds, GMOs,etc.) are not the solutions, you have to think big picture, refer to the three ethics…part of the solution is to not deliberately create problems. When confronted with an existing problem, sure, go ahead and find a solution…but that doesn’t infer you should create future problems. Permaculture is about finding solutions, not about creating problems. Exotics are here to stay, I love exotics, but like all plantings, they should be chosen wisely. Will they cause problems for neighbours, future property caretakers, are they toxic to people, animals, ecosystems?
    Anyone who cares to deliberately plant a declared noxious weed should do some research, and find a more appropriate plant to solve their problem.

  13. Very nice article, I was looking for this plants name for about six months. It it true that I haven`t been too insistent. I remarked the same properties that this tree has, and also there are some good pioneering trees like locust (Robinia pseudoacacia) witch I have seen a lot lately on the hill sides where there is a very deep eroded ditches, birch tree (Beta pendula) who I have spotted on numerous buildings roof tops, in the city on a houses walls, even on a horn. Also I do take pictures when I`m seeing these trees grown in odd places. I have used these species to try to plant a forest using seed balls and I hope to be able to share some positive results on my experiment this year. I live in a temperate climate (Romania, east Europe).

    Thanks one more time for the article!

  14. I think this is very misguided. Invasive tree species have effects that go far beyond what’s mentioned here. They choke out not just other vegetation — in fact, ailanthus emits a toxin that kills other species — they also affect the native ecosystem of birds, mammals and insects, and make it difficult for those cohabitating species to thrive. There’s also my personal preference: I don’t like the tree and I’d be chagrined to see a landscape that’s dominated by this weed. But that’s just me.

  15. This is a very misguided article. These invasive plants are a threat to property and the ecosystem as a whole. Their branches are very weak and likely to cause damage to cars and houses nearby. They also crowd out native species with by their nature. My neighbor was lazy and allowed multiple of these to grow above my house and yard and now I spend hours and hours every year cleaning their detritus off my roof and lawn, picking their incessant weeds, and hoping that they do not crash down on my house. Allowing these oversized weeds to grow is not only irresponsible, it is lazy. Invest a little extra time upfront and plant native species so that you don’t have to spend lots of time and money in the future fixing your mistake. And by-the-way, once you allow one to grow you will be infested with them unless you have lots of extra time on your hands and are very diligent in picking weeds. In my opinion telling people that planting invasive weeds is a good idea is a dangerous seed to plant in someones head. Irresponsible.

  16. You have neglected to mention or, are unaware, that it produces toxins in the surrounding soil. Thus killing or inhibiting many native species. The cedars will most likely never gain a foothold as ailanthus out competes them on r poissons them. Chopping them regularly is not how you control them. They exhibit a threat response and when original tree is damaged it triggers sprouts from rhizome like root system up to 50ft away from original and in a ration of 10:1.
    This tree is also the favorite breeding host for Spotted Lanternflies, a sever crop hazard to fruit trees and other food crop trees that has currently spread across the Eastern seaboard.

    It is seriously reckless of you to spread this misinformed opinion.

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