The Tree of Heaven is an invasive species that grows just about anywhere its seed lands, in the poorest of soils, with very little water, and even out of cracks in cement. However, it is not only its rapid growth and spread that has made the tree of haven one of most dreaded invasive species. It also has a bad record for being allelopathic, preventing other plants from growing nearby. The tree produces a lot of pollen which can cause allergies, and its leaves, branches, seeds, and bark can irritate the skin. If that wasn’t enough, tree of heaven is also the main host for the spotted lanternfly, a highly destructive pest from Asia that was discovered in the northeastern United States in 2014.
|Common Name||Tree of heaven, ailanthus|
|Botanical Name||Ailanthus altissima|
|Mature Size||60-75 ft. tall, 35-50 ft. wide|
|Soil||Loamy, sandy, clay, silt|
|Bloom Time||Spring, summer|
|Flower Color||Yellow, green|
|Hardiness Zones||5-8 (USDA)|
Tree of Heaven Invasiveness
The Tree of Heaven is reported to be an invasive species in over 30 of the 50 US states. It was initially introduced as an ornamental tree and widely planted in cities and towns in the 1800s. It has escaped cultivation and spread vigorously through suckers or seeds, displacing native plant species.
Tree of Heaven can be found throughout the continental United States in zones 5-8, and it grows rapidly; growth of 10 to 15 feet in one year is not unusual. With its dense monocultures, it has taken over fields, meadows, and timbered forests. Because the tree is drought-tolerant and grows in nutrient-poor soil, it easily chokes out native vegetation.
While tree of heaven does not tolerate shade, it encroaches on a forest that has been disturbed, or establishes itself on the edge of the woods. From there, it spreads by suckers or the samaras of female trees which are dispersed by the wind.
Once established, it constantly grows suckers, and not just at its base but 50 or more feet away from the original tree. It only takes the newly sprouted trees about two years to produce seeds on their own. A female tree produces up to 300,000 seeds per year.
What also makes tree of heaven so very invasive is that its leaves, roots, and bark release allelopathic chemicals which prevent other plants from growing. This, in combination with rapid growth and spread, and the ability of the tree to survive droughts and thrive in poor soils, leads to tree of heaven monocultures.
What Does Tree of Heaven Look Like?
Identifying a tree during the dormant season is not always easy, but a mature tree of heaven has a very distinct, rough and fissured bark that looks like the skin of a cantaloupe.
The leaves are long with a central stem and leaflets on either side. Because they are so large—between one and four feet—they can easily be mistaken for several leaves, though it’s actually one large leaf with 10 to 40 lance-shaped leaflets with smooth edges.
The foliage has two characteristics: the underside of each leaflet has two bump-like glands. And the leaves have a repugnant smell similar to burnt peanut butter, wet gym socks, or cat urine.
The leaves are not the only thing that smells in tree of heaven. In the late spring or early summer, yellowish to light green flowers appear on the tree. The panicle-shaped flowers of the male tree have a noxious, skunk-like smell.
After the bloom, the male flowers wither away whereas the female flowers develop into samaras (winged seed pods, also known as helicopter seeds) containing a single seed which mature in the late summer or fall.
How to Get Rid of Tree of Heaven
Small seedlings can be pulled from the ground manually, as long as you remove them with all their roots. This is the easiest after a rain when the soil is wet. If you're unsure if you can get all the roots up when you pull, use a shovel for removal.
The process of removing a full-grown tree of heaven consists of cutting down the tree as close to the ground as possible. Brush off any sawdust that might be on the cut surface and apply a systemic herbicide such as glyphosate, using a paintbrush or an herbicide applicator. This application needs to be done within five minutes after cutting the tree, otherwise the surface will have closed up and the herbicide won’t penetrate the tissue. In the following weeks and months, during the growing season, keep an eye on the stump and remove any new sprouts, suckers, and seedlings, always followed by the same systemic herbicide treatment. It can take several months until the tree stops showing signs of life. Be persistent and patient.
How to Tell the Difference Between Tree of Heaven vs. Sumac
The leaves of both staghorn and smooth sumac are large like the tree of heaven leaves but they have no single leaflet at the end of the leaf. Sumac leaves have serrated edges or teeth, unlike tree of heaven, which has only a few leaflets with teeth at the base of the leaflet, the rest of the margins are smooth.
The panicle-shaped yellow-green flowers of sumac develop into fussy velvety drupes with vibrant red berries.
How to Tell the Difference Between Tree of Heaven vs. Black Walnut
The leaflets of black walnut trees are finely serrated, unlike the tree of heaven leaflets. Walnut leaves have no or a very small non-distinct terminal leaflet. In the spring, the tree has male flowers in the form of long, green catkins and female spike-like greenish flowers. In the fall, black walnuts drop their nuts in green husks that blacken after they drop off the tree.
Why is tree of heaven an invasive species?
The tree of heaven is considered to be an invasive species because it spreads and reproduces rapidly, while also harming or killing other plants in its vicinity. Its leaves, roots, and bark release allelopathic chemicals which prevent other plants from growing.
What are some characteristics of tree of heaven?
A mature tree of heaven has a very distinct, rough and fissured bark that looks like the skin of a cantaloupe. Underside of each leaflet has two bump-like glands and a repugnant smell similar to burnt peanut butter, wet gym socks, or cat urine.
What are non-invasive alternatives to tree of heaven?
Where is tree of heaven native to and how did it come to the United States?
Tree of heaven was is native to China and Japan. It was introduced to the United States in 1784.
Tree-of-heaven. Penn State Extension.
Invasive to Avoid: Tree-of-Heaven. California Department of Fish and Wildlife.