The Problem with Tree of Heaven
Tree of heaven sounds like it must be a great tree, right? It came from China where it grew on steep, rocky ground, often at the tops of mountains, pointing towards the heavens. Introduced to Philadelphia in 1748 by a gardener, the tree was popular because it grew rapidly in urban areas and had few pests or diseases. The problem is that the tree quickly forms dense colonies connected by underground roots. The trees release chemicals from their roots and leaves that prevent other plants from growing. The aggressive roots can damage building foundations and underground pipes.
Photo courtesy of the Missouri Botanical Garden PlantFinder
Tree of Heaven Stinks
Not sure if that tree is a walnut or a tree of heaven? Smell the leaves.If they smell like burnt peanut butter, you've got tree of heaven. Nut trees (walnuts, pecans and hickories) and sumacs (shown in picture) have similar looking leaves, but their leaves have a citrusey smell. Each leaf is actually made up of many leaflets. Both sumac and nut tree leaflets have teeth along the entire edge of the leaf, whereas tree of heaven has only a couple teeth at the base of each leaflet. Tree of heaven has relatively smooth bark and very stout twigs.
Wind Disperses the Seeds
Tree of heaven has separate male and female trees. Female trees produce up to 300,000 winged seeds that are spread by wind. The trees grow in many soil types including heavily polluted sites. It tends to occur on disturbed land, along road and railroad edges, forest edges and in fields. The trees are not shade-tolerant.
Controlling Tree of Heaven
Always wear gloves when working around tree of heaven. The sap contains chemicals that can cause headaches and nausea and even heart problems with repeated exposure. The foliage of small trees can be sprayed with Roundup® Weed & Grass Killer Super Concentrate or Roundup® Concentrate Poison Ivy Plus Tough Brush Killer, according to label directions, to control them. Use care when spraying tree foliage as product can drift to affect nearby desirable plants. Seedlings and small saplings can be hand pulled, dug out or pulled out using a weed wrench taking care to remove all the roots. Larger trees should be cut close to the ground. Freshly cut stumps left lying on the ground can also start to root from the trunks so treat the same as the stump and dispose. Drill 4 to 5 holes into freshly cut stump and immediately pour a Roundup brand concentrate product undiluted into the holes. Once the stump has died, it can be safely removed. Because of tree of heaven's persistence in re-sprouting, any treated area should be monitored the next growing season and sprouts sprayed.
Article by Sylvan Kaufman. Dr. Kaufman is a writer of popular scientific and gardening articles. She is also an ecological consultant.