Hardy between USDA zones 4 and 9, the hop tree or wafer ash (Ptelea trifoliata) is a large shrub or small tree native to the eastern and central US including as far west as Minnesota, Nebraska, Utah, and Arizona. Hop tree is a member of the Rue or Citrus plant family (Rutaceae) the same family as the economically important genus (Citrus) whose members include oranges, lemons, and limes.
In addition to wafer ash, hop tree is sometimes referred to as skunk bush and stinking ash because of the disagreeable odor that emanates from all parts of the plant, particularly the small greenish-white flowers that bloom in late spring that are pollinated by carrion flies. The name hop tree refers to the use of the wafer-like samaras (pictured above) as a substitute for hops. The dark green compound leaves are 2 to 5 inches long and turn yellow in the fall.
Hop tree has a rounded compact habit reaching a height of about 15 to 20 feet, making it a good choice for an informal hedge. Preferring full to part shade, hop tree is low maintenance and tolerates dry to medium soils. Although it has been in cultivation for nearly 300 years, it’s not a particularly popular ornamental tree and is grown primarily for its interesting fruits, which persist into winter.
Wafer ash is listed as endangered in New Jersey and New York and threatened in Pennsylvania.
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