by Ann Farnham, LLA
The Ewing Environmental Commission is sharing its monthly Plant of the Month Series selection for September which focuses on the invasive pest, Ailanthus altissima, the Tree of Heaven.
Tree of Heaven, Ailanthus altissima
“Heaven” in this case does not mean “Heavenly”. On the contrary, this tree is a serious pest; the word “Heaven” is derived from the South Moluccan name Ailanto, which means a tree reaching for the sky.
Ailanthus altissima is native to China, Taiwan, and North Korea. It was first introduced to Europe in the 1740’s and to a Philadelphia gardener in 1784. It has since spread greatly and is now naturalized throughout most of the U.S.A., Argentina, Australia, New Zealand, the Middle East, and Africa. In this country it can be found from USDA Hardiness Zones 4 to 8A. This is reportedly the fastest growing tree in the United States, 3’ to 6’ per year, and it is difficult to control.
Why has it spread so successfully? When it was introduced to the U.S.A. it was used widely as a street tree, in spite of its very offensive odor (some compare it to cat urine, or worse), and it thrived because it required no care and people wanted the shade. It tolerates conditions almost impossible for other tress: very poor soils, a vast pH range, drought, and pollution such as sulfur dioxide, high salinity, low phosphorus, coal dust, cement dust, and ozone. In addition, it sends up new growth from cut trunks, resulting in countless, vigorous sprouts; new trees also come up from the underground stems (rhizomes) and the female tree is a prolific seed producer. The achene, the flat, reddish fruit 1 ½” long and ½” wide, is twisted, thin, and flat, containing one seed, and is very easily carried by wind as it spins. It germinates in cracked pavements, walls, disturbed sites, roadsides, and woodlots, crowding out all other vegetation. Underground pipes and sewer lines are frequently damaged by the trees’ roots. Ailanthus contains an allelopathic chemical which inhibits other plants’ growth, and the foliage is mildly toxic to foraging animals. Deer do not eat it, nor do birds and squirrels. The odor from both male and female trees often causes nausea and headaches in humans, and contact can cause skin rash. It is easy to understand why this plant is called “Arboreal riff-raff”. However, it was subject matter in the book, A Tree Grows in Brooklyn by Betty Smith, and it is mentioned by William Faulkner in Sanctuary.
Tree of Heaven will live about 50 years. It can reach a height of 40 to 60’, normally spreading to a width 2/3 that size. It has an upright, spreading habit and casts abundant shade. The compound leaves, 8 to 24” long, are arranged alternately on a stem, with 13 to 25 stalked, finely fuzzy, oval leaflets. The new leaves are bronzish-purple and mature to a dark green in summer. They have no fall color. When crushed, the leaves smell like rubber. The bark is light colored grey, with longitudinal, lighter streaks. The female trees usually flower in mid June, with yellow-green flowers arranged in panicles on an 18” to 24” stalk. The female flowers are odorless, but the male flowers stink as mentioned above, a smell which attracts pollinators.
Diseases and pests are minimal and do not create lasting damage.
Eradication is a challenge. A young seed sprout can probably be pulled up, but more mature specimens require cutting, and the resultant sprouts then should be treated with Glyphosate (Roundup) or an equivalent. Salt and vinegar and other homemade concoctions will not do the trick. If this tree appears in your yard, get to work!
Ailanthus has been used for “impossible situations”, such as eroded areas in mine runoff, but it is nonetheless regarded as having no landscape value. Extracts from the tree have been used in folk medicine, primarily by the Chinese, to address baldness, dysentery, mental illness, inflammatory conditions, and malaria, among others. The leaves have been used to grow silkworms and the fine-grained satiny wood can be used for cabinetry, although the uneven trunk texture-from rapid growth- causes cracking during drying. Most people feel that its best use is for firewood.
Do not confuse Ailanthus altissima with Black Walnut, Staghorn Sumac, or Ash, which have similar leaves. We addressed Ash in a recent Plant of the Month article, and will be writing about Staghorn Sumac (a non- invasive native which also grows prolifically on roadsides) and Black Walnut soon.