The purple robe locust (Robinia ambigua) is a deciduous tree commonly used in landscape plantings. The tree is known for dark leaves with new growth exhibiting a purple color. In fall, the foliage turns to an attractive yellowish color. The tree produces pink blossom clusters up to 8 inches long in the spring. Purple robe locust exhibits a combination of a relatively rapid growth rate and good longevity, making it attractive to homeowners.
The purple robe locust grows at a rate of between 2 and 3 feet per season under ideal conditions. The tree maintains a rather round shape once it grows beyond the seedling stages and forms a compact tree growing on a single straight trunk.
Ideal Growing Conditions
The purple robe locust is hardy to U.S. Department of Agriculture zone 3, making it an option for gardeners even in the Northern United States. The tree prefers full sun but tolerates limited shade and grows well in a variety of soil conditions, including alkaline and acidic. It also grows well under either wet or dry conditions.
The purple robe locust matures to between 40 and 50 feet tall. Tree growth rate and maturity are roughly the same for the three common cultivars. The Decaisneana, Idahoensis and Purple Robe all exhibit the same basic traits as the more generic plants.
The purple robe locust can live as long as 150 years given ideal conditions. The tree does suffer from root rot and aphid problems, which can shorten the tree's potential life.