Robinia

This group of deciduous trees and shrubs is native to the U.S. and Mexico. They are commonly known as Locust Trees or False Acacias. These trees will grow well in poor, dry soil and in salty, sandy soil near the sea. They are suitable for growing along roads and in cities. R. Pseudoacacia (Black Locust, Yellow Locust or False Acacia) is a tree that can grow from 70 to 80 feet high. It has a wide-spreading head of scraggly branches that are clothed with pretty, green leaves 6 to 12 inches long. They consist of 11 to 23, oval leaflets that are dull bluish-green above and paler beneath. There is a pair of spines at the base of each leaf. Compact, pendulous clusters of fragrant, white flowers are produced in early summer and these are followed by thin, brown pods (resembling Pea pods) containing 4 to 8, small, mottled brown seeds. The wood of this tree is strong, heavy, hard and durable when in contact with the soil. It is used for making posts, railroad ties, fences and other various supplies. R. Kelseyi is a small tree or tall shrub that has small leaves and clusters of rose-colored flowers in early summer. Its seedpods are covered with reddish bristles. R. hispida (Rose Acacia) is a shrub with brownish branches covered with rigid bristles. The leaves are usually larger than R. Pseudoacacia. In May, small clusters of rose-colored flowers are produced.

Pot Cultivation

Locust Trees can be grown in all types of soil; however, they will grow best in well-drained loam, in full sun. The branches of these trees are brittle, therefore, should be pruned while they are young to encourage the development of sturdy ones. They also need to be pruned in order to form a well-shaped, compact head. Pruning should be done in late summer or fall, because they will bleed if pruned in the spring. Any suckers that are produced at the trunk's base should be removed.

Propagation

It is better to increase the trees by seed, but suckers that grow up from the base can be used. Seeds may be sown in a frame of sandy soil as soon as they are ripe or stored and sown the following spring. They will germinate faster if sown in the fall as soon as they are ripe. Named varieties of these trees are grafted on stocks of R. Pseudoacacia. As your young plants are growing, make sure the tree kinds develop one central trunk by removing any other suckers. They are liable to break in storms if there is more than one trunk.

R. Hartwigii

VARIETIES

Tree -

• R. Pseudoacacia (70-80 feet high) & var. inermis, Decaisneana, unifolia, Rehderi, Bessoniana, semperflorens, pendula, rectissima, umbraculifera (20 feet), Friesia;
• R. viscosa (40 feet);
• R. Kelseyi;
• R. luxurians (30-35 feet);
• R. Idaho (25-35 feet).
  Shrub -
• R. hispida & var. macrophylla;
• R. Hartwigii;
• R. Boyntonii;
• R. Elliott