Ailanthus altissima or Tree of Heaven, is a notorious, fast growing, invasive plant which left unchecked can quickly become a large shrub or substantial tree. An urban nuisance, you’ve likely seen it jumping out of cracks in sidewalks, pushing through established shrubs and lining alleys where little else will flourish. I recently found a seedling growing in the corner of my pebble-lined basement window well, a testament to its ability to survive in poor soil with little moisture. It will grow most anywhere except very dense shade and swamps and is capable of choking out desirable plants, forming thickets and damaging sewer lines or building foundations. The vigorous lateral root system sends up numerous suckers and the plant will also easily establish by seed. Remember the novel A Tree Grows in Brooklyn? The title’s tree is Tree of Heaven – aptly used as a metaphor for determination and survival.
In the late 1700’s the tree was brought to this country from China and was heralded for its rapid growth. According to the U.S. Forestry Service, a young specimen can grow 24′ in the first four years and a mature tree can easily reach 50’ or more and produce over 300,000 seeds annually.
Ailanthus altissima has several distinguishing characteristics detailed in this Colorado State University publication. Sometimes mistaken for Sumac, Tree of Heaven leaves are pinnately compound (made up of several elongated leaflets) with a glandular notched base and smooth edge. The smooth leaflet margins differentiate the plant from Sumac, which has a jagged leaf margin. When Tree of Heaven foliage is crushed it has a foul odor resembling rancid peanut butter, hence another common name, Stink Tree. Clusters of yellow-green flowers emerge in spring; later in the season, female plants produce tan to reddish, single-winged samaras or seed pods. Large triangular leaf scars are visible on the twigs and are another defining characteristic of this notorious plant.
To eliminate Tree of Heaven, vigilantly pull small seedlings by hand. If the plant is well established, cutting it down will trigger the root system to produce an army of suckers, which in short order can result in a small colony. An effective treatment is to make numerous slashes on the trunk or drill holes into the bark and immediately apply a full strength herbicide containing Triclopyr on the openings. Waiting even longer than 30 seconds to apply the chemical renders the treatment ineffective, as the plant quickly seals the wound in the cambium layer and prevents the herbicide from reaching the root system. It can take multiple applications to kill a well established plant. As always, follow all instructions for the safe use of chemicals. Simply digging mature suckers up without the use of herbicide may be effective over time, but the bossy root system is likely to make this a frustrating and counterproductive exercise.
Image 1 (seedling): Google Free Image
Image 2 (tree): Annemarie Smith, ODNR Division of Forestry, Bugwood.org
Image 3 (flower): Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Image 4 (tree scar): Daniel Herms, The Ohio State University, Bugwood.org
Linda McDonnell, a Denver County Master Gardener