LOCUST

FAMILY: Papilionaceae | GENUS: ROBINIA

TYPE
  • Shrubs
  • Trees
  • Deciduous
SUN EXPOSURE
  • Full Sun
WATER
  • Regular Water
  • Moderate Water
  • Drought Tolerant
PLANTING ZONES
  • US (Upper South) / Zone 6
  • MS (Middle South) / Zone 7
  • LS (Lower South) / Zone 8
  • CS (Coastal South) / Zone 9
SPECIAL FEATURES
  • Poisonous/Toxic

Plant Details

Fairly fast-growing plants, well adapted to hot, dry regions. Leaves are divided like feathers into many roundish leaflets. Clusters of white or pink, sweet peashaped flowers bloom from midspring to early summer, followed by beanlike pods about 4 inches long. Locust trees tolerate poor soil and can get by on little or no water, but they do have some drawbacks: Wood is brittle, roots are aggressive, and plants often spread by suckers.

idaho locust

robinia x ambigua

  • Tree.
  • Hybrid between Robinia pseudoacacia and Robinia viscosa, a seldom-grown pink-flowering locust.
  • The following are the best-known selections.

Decaisneana

  • To 4050 feet tall, 20 feet wide.
  • Flowers are like those of Robinia pseudoacacia, but color is pale pink.

Idahoensis

  • Shapely tree 2540 feet tall and 1530 feet wide.
  • Reddish bronze new growth and bright rose-pink flowers in 8 inches clusters make it one of the showiest locusts.
  • Bears no seedpods.
  • Thrives under arid conditions; good choice for western parts of Texas and Oklahoma.

rose acacia, bristly locust

robinia hispida

  • Shrub.
  • Native from Virginia and Kentucky to Georgia and Alabama.
  • Small, showy shrub that will form colonies from root suckers.
  • Extremely invasive in good soil.
  • Grows to 7 feet (sometimes 10 feet.) tall, 8 feet wide.
  • Bristly stems; blue-green leaves to 10 inches long, with 7 to 15 leaflets.
  • Rose or pale purplish pink flowers in dangling, 4 inches clusters in late spring.
  • Tolerates dry, poor soils.
  • Use on dry banks, in naturalized settings.

black locust

robinia x margaretta

  • Tree.
  • Hybrid between Robinia hispida and Robinia pseudoacacia.
  • Grows at a moderate rate into an open, rounded tree 1530 feet high and wide.
  • Bristly stems; leaves to 8 inches long, with up to 19 leaflets.
  • Fragrant, inches pink flowers hang in clusters to 7 inches long.
  • Flowering Globe reaches 18 feet tall and wide, with 8- to 10 inches clusters of dark pink flowers.
  • Pink Cascade ('Casque Rouge') reaches 15 feet tall and wide, has purplish pink flowers and pinkish new growth.

robinia pseudoacacia

  • Tree.
  • Native to eastern and central U.S. Fast growth up to 4075 feet tall, 3060 feet wide, with rather sparse, open branching habit.
  • Deeply furrowed brown bark.
  • Thorny branches.
  • Leaves divided into 7 to 19 leaflets, each 12 inches long.
  • White, fragrant, - to inches-long flowers are held in dense, pendent clusters 48 inches long.

Black locust is little valued in its native territory, but it is a favorite in Europe. Rot-resistant wood is sought after for fence posts. Bees make delicious honey from the nectar of its flowers. The tree manufactures its own fertilizer through nitrogen-fixing root nodule bacteria and can colonize the poorest soil. Given some pruning and training in its early years, it can be a truly handsome flowering tree, but locust borer limits its usefulness in many regions; locust leaf miner is also a damaging pest, especially in the Upper and Middle South.

Often used as street tree, but not good in space between sidewalk and curb or under power lines. Wood is extremely hard; suckers are difficult to prune out where not wanted.

Recommended selections include the following.

clammy locust

Frisia

  • To 50 feet tall, 25 feet 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 810 feet tall and 1215 feet wide.
  • Picturesquely twisted branches; few flowers.

Pyramidalis

  • ('Fastigiata').
  • Narrow, columnar, to 50 feet tall, 10 feet wide.

Tortuosa

  • Slow grower to 50 feet tall, 30 feet wide, with twisted branches.
  • Few flowers.

Umbraculifera

  • Dense and round headed, to 20 feet tall and wide.
  • Usually grafted 68 feet high on another locust to create a living green lollipop.
  • Very few flowers.

robinia 'Purple Robe

  • Tree.
  • Hybrid of uncertain parentage often sold as Robinia pseudoacacia 'Purple Robe'.
  • Resembles Robinia x ambigua 'Idahoensis' but has darker, purple-pink flowers, reddish bronze new growth; blooms 2 weeks earlier and over a longer period.
  • Suckers from the rootstock spread and reseed heavily.

robinia viscosa

  • Tree.
  • To 40 feet tall, 20 feet wide.
  • Rare.
  • Native to eastern U.S., from North Carolina to Alabama.
  • Leaves are divided into 12 to 24 leaflets.
  • Deep pink flowers in 3 inches clusters appear in late spring.
  • Common name refers to sticky glands on the stems, leafstalks, and seedpods.

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