For years I have been pulling volunteer tree seedlings from my garden. I thought they were walnuts, planted by squirrels preparing for winter. Some of the seedlings got away from me and became saplings with huge, destructive root systems. These saplings have established at the bases of desirable plants, such as my rhododendrons and raspberries, and along our house foundation. They are Ailanthus altissima, “Tree-of-Heaven,” a truly noxious invasive species imported from China hundreds of years ago. I found the seed-producing trees less than a block away from our house. In walking the neighborhood, I have seen many of these trees in parking strips. Tree-of-Heaven can be confused with staghorn sumac, black walnut, and hickory.
One of the many problems with Tree-of-Heaven is the fact that it’s a prolific seed producer. The winged seeds travel widely and germinate easily. The plant has heavy, aggressive root systems that have been known to crack foundations and overtake desired plantings. It easily adapts to all kinds of environments: gardens, forests, and roadsides. The Ailanthus altissima produces destructive allelopathic chemicals in its leaves, roots, and bark that can limit or prevent the establishment of other plants. For some people, contact with the pollen or sap can cause allergies and dermatitis.
What can we do to control this plant? First of all, don’t plant it. Be vigilant. Become familiar with what the seedlings look like and pull them immediately. The root system, even on a seedling, is impressive. Manual removal can work on small seedlings and saplings, but all roots and root fragments must be removed. New growth sprouts from even small root fragments, and can appear 50 feet from a mature Ailanthus altissima tree.
Since I haven’t been certain that I can get all the sapling roots out, I have very reluctantly resorted to systemic herbicidal control in addition to digging (see the excellent references below). From July to onset of fall color, when the plant is drawing fluids and carbohydrates back to its roots prior to going dormant, I paint the herbicide onto the cut stem of the Tree-of-Heaven. I have also painted herbicide on the new growth of the saplings, but that seems to damage only the leaves. The roots must be damaged to control the tree. I would never apply these herbicides as a spray since many surrounding shrubby plants would be destroyed. These herbicides are the type used to control rampant blackberries.
Tree-of-Heaven is pretty, but it is serious destruction hiding in an attractive form. Useful identification pictures can be found on the following sites: https://extension.psu.edu/tree-of-heaven and https://www.techlinenews.com/articles/2014/tree-of-heaven-a-devil-in-disguise (guidance on herbicides.)