Introduction
A fast-growing deciduous tree, umbrella black locust grows to about 20 feet tall and wide. The weeping, round habit forms a canopy much denser than the species casting dense shade below the tree. The 6- to 14-inch-long, dark green leaves, made up of multiple leaflets, are some of the last to appear in spring and often drop early in the autumn. Flowers irregularly with only a flower 'here and there' in the crown. The 2- to 4-inch-long, dark red to black, leathery seeds pods which sometimes follow will persist on the trees throughout the winter.
Credit: Ed Gilman, UF/IFAS
General Information
Scientific name: Robinia pseudoacacia
Pronunciation: roe-BIN-nee-uh soo-doe-uh-KAY-shuh
Common name(s): Umbrella black locust, umbrella common locust
Family: Leguminosae
USDA hardiness zones: 4A through 8B (Fig. 2)
Origin: native to North America
Invasive potential: weedy native
Uses: specimen; shade
Availability: not native to North America
Description
Height: 15 to 20 feet
Spread: 20 to 25 feet
Crown uniformity: symmetrical
Crown shape: weeping, round
Crown density: dense
Growth rate: fast
Texture: fine
Foliage
Leaf arrangement: alternate (Fig. 3)
Leaf type: odd-pinnately compound
Leaf margin: entire
Leaf shape: elliptic (oval), oblong, obovate
Leaf venation: pinnate
Leaf type and persistence: deciduous
Leaf blade length: less than 2 inches
Leaf color: green
Fall color: yellow
Fall characteristic: not showy
Flower
Flower color: no flowers
Flower characteristics: no flowers
Fruit
Fruit shape: no fruit
Fruit length: no fruit
Fruit covering: no fruit
Fruit color: no fruit
Fruit characteristics: does not attract wildlife; no fruit; fruit/leaves not a litter problem
Trunk and Branches
Trunk/bark/branches: branches droop; showy; typically one trunk; thorns
Pruning requirement: needed for strong structure
Breakage: susceptible to breakage
Current year twig color: brown
Current year twig thickness: thin
Wood specific gravity: 0.69
Culture
Light requirement: full sun, partial sun, or partial shade
Soil tolerances: clay; sand; loam; acidic; alkaline; well-drained
Drought tolerance: high
Aerosol salt tolerance: high
Other
Roots: can form large surface roots
Winter interest: yes
Outstanding tree: no
Ozone sensitivity: unknown
Verticillium wilt susceptibility: susceptible
Pest resistance: sensitive to pests/diseases
Use and Management
The tree is best used as a specimen for an outstanding ornamental effect. Plant on 20- to 30-foot-centers along an entrance road or along highway medians. This should be a very adaptable, pretty tree for urban plantings, but is usually not grown by nursery operators. The root suckering and invasive root system allows the species to quickly spread into surrounding landscapes. This feature should be considered when placing black locust in the ornamental garden, although the cultivar may not sucker as much.
Although the wood of black locust is reputed to be extremely strong and durable (pioneers used it to fashion nails for building ships and houses), the branches are brittle and subject to damage in high winds. This may be due largely to the tendency for the branches to form a narrow angle with the trunk and to grow aggressively relative to the trunk. This can be partially corrected by pruning the major branches so they grow to no more than about half the size of the trunk. Try to space the major branches along the trunk as best you can to develop a strong tree which will stay together. This will be difficult since the tree is usually purchased with the major branches well developed and most of them originate from one point on the trunk. Able to tolerate drought, salt, and poor soil, black locust will grow in full sun or partial shade on almost any soil except that which is permanently wet. The species is a tough tree which will grow on the toughest sites, and there is no reason to believe this cultivar will respond differently.
Pests
Locust borer is a serious pest although borer-resistant clones are now being developed. Also bothered by carpenterworm, locust leaf miner, and scales. Leaf miner is a universal problem on the species, and the trees along the highways in the south can be seen in summer riddled with damage from this pest.
Diseases
This tree is susceptible to canker, leaf spot, and powdery mildew.
