By Judy Kunz, Colorado Master Gardener
There is an innocuous looking tree that has been quietly invading this continent. It is similar in appearance to and often confused with the native Smooth Sumac (Rhus glabra), but this badly behaved plant comes to a neighborhood uninvited, out competes other plants and brings thousands of its offspring to stay over. You’ll find it lurking in vacant lots, along fence lines, in alleys, even popping up in flower gardens and sidewalk cracks.
The not-so-heavenly Tree of Heaven (Ailanthus altissima) is a native of northern China. Introduced as an ornamental in 1784, it is considered an invasive weed that can now be found in most states, eastern Canada and Hawaii, and it shows no sign of slowing its spread. Like many invasive plants originating from other continents, there are few natural controls in place to restrain it.
If its invasive habits aren’t enough, its roots are allelopathic, releasing chemicals that can inhibit germination or growth of nearby plants. Its toxicity increases during periods of low precipitation and high temperatures. It is drought and pollution tolerant and is a prolific seed producer, a mature female tree dispersing more than 300,000 seeds per year.
Tree of Heaven can be difficult to eradicate, requiring persistent removal techniques. Seedlings can be pulled by hand when the soil is moist but can resprout if the entire root is not taken. Systemic herbicides should be applied in mid to late summer when the tree’s energy is directed toward its root system. Several applications may be necessary. If the tree is removed by cutting the trunk, a brush and stump killer containing triclopyr can be applied to the freshly cut stump to prevent sprouting.
Tree of Heaven characteristics:
- Compound leaves can be 12” to 48” long and contain 11-41 leaflets
- Leaflets have smooth margins with glandular teeth at the base near the stem
- Leaves give off an offensive odor when crushed
- Can grow rapidly to 40’ wide x 50’ tall
- Both male and female trees bear flowers that hang down and are orange to brown in color
- Shallow roots can extend 50’ to 90’ from tree & may sprout
- Extremely invasive, crowding out native vegetation
Smooth Sumac characteristics:
- Leaf is 30” to 45” long and contains 11-31 toothed leaflets
- Shrub or small tree that can grow to 15’ tall
- Flower clusters are yellow and tend to point upward
- Fall fruit clusters point upward and are dark red
- Moderately invasive