Weed: Ailanthus altissima, commonly called Tree-of-Heaven, Chinese sumac, stinking sumac.
Description: This is an invasive tree. It readily grows in the USDA hardiness zones 4 through 8. The leaves are pinnately compound with 11 to 41 leaflets, with prominent glands on the back of each leaflet. The leaf can reach 3 feet long. Tree-of-heaven is easy to confuse with walnut or sumac. The tree can reach 70 feet or more in height and the crown 80 feet wide.
It is a dioecious plant, with male trees and female trees, but some trees may have perfect flowers, meaning the flowers contain both male and female reproductive parts. The inflorescence (cluster of flowers) is a 4- to 7-inch long panicle (think of a lilac blossom) that that can appear orange-red in the fall that persists through the winter. Male flowers have a strong bad odor, while the female flowers are odorless. Fruits are one-seeded, dry schizocarps or with wings also referred to as samaras.
Not only is the tree drought tolerant, it is quite tolerant of severe air pollution. This made it popular as a street tree for many years.
Growth rate for the tree-of-heaven is fast; it can grow up to 5 feet a year. The wood is brittle. It is usually short-lived for a tree, lasting 30 to 70 years. Twigs have a brown pith with an unpleasant odor described as similar to burnt peanut butter.
Where: This tree is found in disturbed soils, fencerows, roadsides, woodland edges, and succession forests. It can spread from the edges and crowd out desirable trees. The tree-of-heaven is often planted in urban areas as a street tree. It does well in poor soils.
Propagation: A mature tree can produce 350,000 seeds a year. Seeds can be blown by wind, float on water, or be transported by birds. Trees also reproduce by suckers.
Historical: The tree is native to central China and Taiwan. Tree-of-heaven was introduced to the U.S. through Philadelphia in 1784 as a garden plant. Chinese immigrants who came to California to work on the railroad introduced the plant in that state. It was introduced to New York from English stock in 1820, where tree-of-heaven was planted as an ornamental. Tree-of-heaven was commercially available in eastern nurseries by 1840. The tree-of heaven is the namesake for Betty Smith's 1945 classic entitled "A Tree Grows in Brooklyn".
What: Rarely are trees considered weeds, but tree-of-heaven is one that is, or should be. Once it gets a foothold, it is difficult, if not impossible to eradicate. Some people let the tree get started in their yards because it has an exotic look reminiscent of palms when the tree is young.
Pros: The strong foul odor of the male flowers attracts honeybees, flies, beetles, and other insect pollinators.
Medicinal: The few supporters of the tree say it has beneficial healing properties. The root bark of this plant is said to be an antibiotic used to treat malaria and kill parasitic worms. Extracts from the tree are said to treat tumors. Other folk remedies include treatment for diarrhea, asthma, cramps, epilepsy, a fast heart rate, gonorrhea, malaria, and tapeworms. It also has been used as a bitter and a tonic. There seems to be a long history of medicinal use in Chinese folk medicine. Most responsible websites give warnings regarding safety as many parts of the plant are considered toxic. Leaves are considered poisonous to domestic animals. There are reports of people getting rashes after handling the tree.
Cons: It is considered a "dirty" tree as it readily drops twigs and branches due to its brittle wood. The tree roots are allelopathic, meaning they give off a toxin that acts as an herbicide and can inhibit growth of other trees and plants. Walnut trees have this characteristic, as well.
Besides having allelopathic roots, another reason the tree-of-heaven is invasive is that it is difficult to kill. If an established tree is cut down without pre-treating with an herbicide, the roots go into stress mode and hundreds of shoots sprout, most of which could turn into trees. In Bellevue, Nebraska, the tree-of-heaven has made major inroads in the forest of Jewel Park. For details of managing this invasive tree, go to the USDA Invasive Species Information site. This site is not available due to the lapse in federal funding as of October 1. Hopefully it will be accessible soon!
When the gypsy moth caused cutting of forests in the East, the ailanthus inhibited the oak forests from regenerating. Speaking at the University of Pennsylvania, Dr. Mark Kasson of Virginia Tech said, "There are other invasive tree species in Pennsylvania, but the ailanthus, by far, has been here longer and does more damage than any other invasive tree. It's the number one cause of native regeneration failure in clearcuts in Pennsylvania."