These fairly fast-growing trees are well adapted to hot, dry regions. Leaves are divided like feathers into many roundish leaflets. Clusters of white or pink, sweet pea–shaped flowers bloom from midspring to early summer, followed by bean-like pods about 4 in. long.
Locust trees tolerate poor soil and can get by on little or no water, but they do have some drawbacks: their wood is brittle, roots are aggressive, and the plants often spread by suckers.Robinia neomexicana
Native from California’s mountains to Arizona and New Mexico, this thorny plant usually grows to about 6 ft. tall and wide, but can become a 30-ft. tree. It produces drooping, 6-in. clusters of inch-wide pink flowers.
Native to the eastern and central United States. Fast growth to 40–75 ft. tall and 30–60 ft. wide, with a rather sparse, open branching habit. Deeply furrowed brown bark. Thorny branches. Leaves are divided into 7 to 19 leaflets, each 1–2 in. long. White, fragrant, 1/2–3/4-in.-long flowers are held in dense, pendent clusters that reach 4–8 in. long.
Little valued in its native territory except as a source of honey and fence posts, it has been widely planted (and has subsequently escaped) in much of the West, including California’s Gold Country. It manufactures its own fertilizer through nitrogen-fixing root nodule bacteria and can colonize the poorest soil. With some pruning and training in its early years, it can be a truly handsome flowering tree. Has been used as a street tree but is a bad choice for narrow parking strips or under power lines. Wood is extremely hard and tough; suckers are difficult to prune out where soil is not watered.
‘Frisia’. Grows to 50 ft. tall and 25 ft. wide. New growth is nearly orange; mature leaves are yellow, turning greener in summer heat. Thorns and young wood are red.
‘Lace Lady’ (‘Twisty Baby’). Dwarf to 8–10 ft. tall and 12–15 ft. wide. Picturesquely twisted branches; few flowers.
‘Pyramidalis’ (‘Fastigiata’). Narrow, columnar, to 50 ft. tall and 10 ft. wide.
‘Tortuosa’. Slow grower to 50 ft. tall and 30 ft. wide, with twisted branches. Few flowers.
‘Umbraculifera’ (‘Inermis’). Dense and round-headed tree, to 20 ft. tall and wide. Usually grafted 6–8 ft. tall on another locust to create a living green lollipop. Few flowers.Robinia x ambigua
A hybrid between R. pseudoacacia and R. viscosa, this seldom-grown, pink-flowering locust grows to 40 ft. tall and nearly as wide. Its varieties are better known.
‘Decaisneana’. Grows to 40–50 ft. tall and 20 ft. wide. Flowers are like those of R. pseudoacacia, but the color is pale pink.
‘Idahoensis’ (Idaho Locust). Moderately fast growth to a shapely 40 ft. tall and 30 ft. wide. Bright magenta-rose flowers in 8-in. clusters; one of the showiest of locusts in bloom. Good flowering tree for Rocky Mountain gardens.
Shrub or tree. Native to Europe, North Africa, and Asia. Shrubby, upright growth to 20–30 ft. ta...
Grows to 3–4 ft. tall and 4–6 ft. wide. Narrow green or gray-green leaves are 1 1/2 in. lo...
The species is rarely seen in gardens; it has been replaced by showy large-flowered hybrids valued for...