The tree of heaven (Ailanthus altissima), also known as Chinese sumac, copal-tree, stink tree, and varnish tree, is a problematic exotic invasive species in Iowa. It is often confused with sumac; however, the tree of heaven can be distinguished by the foul odor it emits.
Tree of heaven produces many seeds, grows extremely quickly, and can out-compete native plants. It can rapidly take over a site and form dense thickets. Tree of heaven is also known to produce allelochemicals that prevent other plants from growing around it.
Habitat: Disturbed areas, especially floodplain areas and wooded drainages that are commonly disturbed by flooding, fields, fence rows, roadsides, woodland edges, and forest openings.
Hardiness: Zones 4 through 8
Growth Rate: Fast
Mature Shape: Rounded
Height: 70-100 Feet
Width: 35-50 feet
Site Requirements: Full sun on well drained moist soil, but can survive almost anywhere
Flowering Dates: April - July
Seed Dispersal Dates: Fall - Winter
Seed Bearing Age: 2-3 years
Seed Bearing Frequency: Yearly
Seed Stratification: Prechill for 2 months at 34°F to 40°F
It is a deciduous tree that can grow 40 to 60 feet tall, maximum height of 89 feet, with a trunk diameter of 2 to 3 feet. The leaves are alternate, pinnately compound, 1 to 3 feet long, with thick smooth petioles; having 11 to 41 leaflets, each 1 to 2 inches long, ovate-lance shaped, unequal base, entire margins with teeth at the base and dark green on top and paler underneath. The fruit or seeds are winged papery samaras; red, yellow, and green, and hang in dense clusters.
In June the pistillate trees bear large clusters of seeds, and the staminate trees emit a malodorous stench. The tree of heaven grows rapidly and is very difficult to eradicate once its established – competes aggressively with more desirable native trees.
A native to China and Taiwan and naturalized in North America – commonly cultivated. Considered an invasive species along roadsides, and neglected property, especially in and around urban areas.
The effectiveness of mechanical control on tree of heaven is limited. An important growth feature that makes control challenging is the tendency of tree of heaven plants to produce many sucker plants after being cut, which often makes the infestation worse. Therefore, cutting and prescribed fire are not recommended for controlling tree of heaven. In small areas, young seedlings can be pulled or dug up, especially when soil is moist to allow for easier removal. All roots and root fragments must be removed to prevent new plants growing from any pieces left behind. Chemical control is the most effective treatment. However, tree of heaven is very tough to control, and second-year or follow up monitoring is critical. Even with chemical control, monitoring the site should continue to make sure seedlings and potential suckers and root sprouts are treated. Go to our chemical control of unwanted vegetation article for information on specific herbicides to use. Check out our invasive species page to learn more about invasive species in Iowa.