Family: Papilionaceae
Common Name: Locust

Originally from North America, these 20 species of deciduous flowering shrubs and trees are useful for street plantings as they grow very rapidly and are able to withstand pollution. They are also grown as ornamentals for their fresh, green foliage and decorative, pea-like flowers which may be white, pink or mauve. Most species have thorned branches and flower in summer.

Species

R. x ambigua, zone 3, is a small tree with pink flowers and compound leaves. Cultivar 'Bella-rosea' produces deep pink flowers. R. bispida, rose acacia, zone 5, looks very pretty in summer when covered with masses of deep rose pink flowers. The leaves are long and fern-like. It grows to 2 m (6 ft).

R. pseudoacacia, false acacia or black locust, zone 3, grows to about 25 m (80 ft) in its habitat, but only to about 10 m (33 ft) in cultivation. It has graceful, prickly branches and fern-like leaves. The fragrant, white, pea-like flowers are very attractive to bees and are followed by reddish brown seed pods. Many cultivars are available: some have coloured foliage, others have pendulous growth habits and variable flowering habits. Cultivar 'Frisia', golden robinia, is the variety most commonly grown. It is thorn-less, with golden foliage.

R. viscosa, clammy locust, zone 3, grows to around 13 m (42 ft). The foliage colours attractively in autumn to a golden yellow. The long clusters of lovely, rose pink flowers, with red calyces, are attractive to bees.

Cultivation

Robinias will grow in any soil, ideally reasonably fertile, but will also succeed in poor and very dry conditions. The ideal soil is moisture-retentive vet well drained. Choose a position in full sun, but sheltered from wind, as these trees have very brittle wood. Some species, particularly R. pseudoacacia, sucker freely and this may be a problem if the suckers appear in lawns. Avoid digging around the trees as this can disturb the roots and cause suckering. Propagate species from seed sown in autumn, from root cuttings in winter or from rooted stickers in early spring. Cultivars are budded in summer.

Climate

There are species suited to various climatic zones.