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Locust - Black

BOTANICAL NAME:    Robinia pseudoacacia
PRONUNCIATION: row-BIN-ee-ah SUE-doe-ah-KAY-see-ah
FAMILY:   Fabaceae (Legume Family)
TYPE:     Deciduous shade tree
HEIGHT:   40 to 50 feet
FINAL SPACING: 20 to 30 feet

Full sun, sandy roadsides and fencerows but likes deep, well-drained, calcarious (high calcium) soils. It is not native to Texas but has naturalized here quite well. Black locust is often seen in
abandoned fields and old home sites. It is native to Georgia, Oklahoma, Arkansas
and northeast to New York.

It is an upright and spreading tree with small oval leaflets on large compound leaves that have yellow fall color. It is a fast growing tree with fragrant white flowers in the spring.

The flowers are fragrant and white in the late spring from May to June. They are loose hanging racemes 4 to 5 inches  or longer. The individual flowers are bonnet shaped and about an inch long.  The fruit is a legume that ripens in the fall. It is brown, flat and of course bean-like since this plant is a legume. The seed inside the pods are kidney shaped.

The bark is a light gray to reddish brown, smooth when young, but deeply ridged on mature trees. The trunk is sometimes twisted and has thorns that are paired or scattered individually. Twigs are zig-zag in shape and are very brittle.

Leaves are compound with small oval leaflets that are yellow in the fall. The leaves are 8 to 14 inches long. There are 7 to 19 leaflets per leaf and the leaflets are ½ inch to 2 inches long.

Black locust grows fairly easily in most well-drained soils and requires a minimum amount of water and fertilizer.

Other than being short lived it has very few serious problems. It is susceptible to attack of locust borer and leaf miners but both can be controlled with healthy soil and organic pest control.

Can be easily grown from seed. Seed germination can be increased by soaking in hot water or liquid humate. Beds or pots should be kept moist but not wet. No mulch or shade is required. Damping off is somewhat of a problem but can be eliminated with the use of cornmeal in the potting soil.

Black locust is very difficult to get rid of once established because of root sprouts. Its wood is one of the strongest and most durable in North America. The leaves close slightly at night appearing to go to sleep. The inner bark, young leaves and seed are toxic to livestock and humans. Children have been poisoned by sucking fresh twigs or eating either bark or seed according to Shinner and Mahler’s book Flora of North Central Texas. Black locust is a beautiful tree and should be more in small gardens and courtyards when flower color and fragrance is important and long life is not.


 new growth (25045 bytes)

flowers (40316 bytes)

Flowers are showy, pea-like and occur in pendulous clusters 4 to 8 inches long. They are pink, very fragrant and bloom in late May to early June for about a week.

locust,purplle robe1a.jpg (6061 bytes)

Foliage consists of alternate, pinnately compound leaves. These leaves are 6 to 14 inches long and have 7 to 9 elliptic-shaped leaflets. Color is a dark, dull blue-green. New growth is spiny and a purplish-red and retains some undertones of this color into summer.  Fall color is an unimpressive yellowish-green.    

 seedpods with seeds (22726 bytes)Fruit consists of a flat, 2 to 4 inch brown pod that matures in October and persists into winter. .

Bark is gray with rope-like ridges and interlacing furrows. Branches have spines that are paired, 2 at each leaf.

   .bark (28303 bytes)          branch with spines (33338 bytes)


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