Not native to Iowa, the black locust (Robinia pseudoacacia) is included here because it has been planted so widely over the state, has escaped from cultivation and is sometimes found growing in mixture with native species. Its natural range extends from Pennsylvania southwest ward to Alabama and west ward to southern Illinois. It has been planted widely in Iowa for post production and erosion control. The tree often suffers extensive damage from the locust borer insect.
Hardiness: Zones 4 through 8
Growth Rate: Aggressive; Rapid
Mature Shape: Upright to spreading ovular shape
Height: 50 feet
Width: 25 feet
Site Requirements: Prefers rich, deep, moist, well-drained, and full to partial sun. However, commonly found in poor soil conditions, especially thin and near limestone outcrops.
Leaves: Alternate, compound, with thorns or spines
Flowering Dates: May - June
Seed Dispersal Dates: September - April
Seed Bearing Age: 10 years
Seed Bearing Frequency: Yearly or bi-yearly
Seed Stratification: Soak seeds in warm water for 24 hours.
The leaves are pinnately compound with 11 to 15 leaflets 1 to1-1/2 inches long, rounded at both ends and with smooth margins. The twigs are crooked and angular with short, stout, single, unbranched thorns, one-half inch long. The fruit is a dark, red-brown, flexible pod 3 to 4 inches long, containing small, reddish brown bean-like seeds. On young branches the bark is smooth and greenish to brown in color. On older branches and trunks it is broken into a network of coarse, deep ridges and is gray to gray-brown in color.