Common Name: Black Locust

General Information

Robinia pseudoacacia is a spiny, deciduous tree with an open, irregular crown; it can grow 15 - 30 metres tall. The bole is often forking, slightly angled, and often crooked, with a diameter of 30 - 76cm. The plant will often produce suckers quite freely, and can form thickets[, ].
The plant is often harvested from the wild as a medicine, source of materials and sometimes as a food. It is often grown as a street and ornamental tree[].
Robinia pseudoacacia is widespread in its natural range and it has been introduced and is now naturalized in many countries (Asia, Africa, Australia, New Zealand). Many subpopulations are known to occur within the protected area network and no major threats to the species are known at present. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2012)[].
Robinia pseudoacacia often escapes from cultivation and can become naturalized. It is considered a noxious weed in some parts of the USA outside its native range, and is also considered to be invasive in many other countries of the world[].

Known Hazards

All parts of the plant (except the flowers) and especially the bark, should be considered to be toxic[, , ]. Cases of human fatallities have been recorded[]. Symptoms of poisoning include dilated pupils, feeble pulse, severe vomiting, and a death-like pallor []. The plant is also said to be toxic to livestock, though sometimes it is deliberately used for forage by farmers etc[]. Cooking the plant is said to destroy the toxins.
Humans may get dermatitis from exposure to black locust wood

Botanical References

, ,

Range

Eastern N. America - Appalachian and Ozark mountain ranges in Pennsylvania, West Virginia, Kentucky, Georgia, Illinois, Missouri, Oklahoma

Habitat

Woods and thickets[], especially in deep well-drained calcareous soils[].

Properties

Weed Potential	Yes
Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	25.00 m
Growth Rate	Fast
Pollinators	Bees, Insects, Humming birds
Cultivation Status	Ornamental, Wild

Cultivation Details

Robinia pseudoacacia is a plant of the temperate zone, where it is found at elevations up to 3,300 metres. It grows best in areas where annual daytime temperatures are within the range 15 - 32°c, but can tolerate 6 - 40°c[]. When dormant, the plant can survive temperatures down to about -35°c, but young growth is more tender and can be severely damaged at -1°c[]. It prefers a mean annual rainfall in the range 450 - 700mm, but tolerates 300 - 1,600mm[].
A very tolerant plant, it grows best in full sun but tolerates some shade. It succeeds in any well-drained soil, preferring one that is not too rich[, ]. Succeeds in dry barren sites, in hot dry positions, in somewhat saline soils, and is tolerant of atmospheric pollution[, ]. Plants are drought tolerant, able to withstand a dry period of 2 - 6 months[]. Prefers a pH in the range 5.5 - 6.5, tolerating 4.5 - 8.2[]. The plant has survived on acid strip-mine spoil site with a pH of 2.85[].
A fast-growing tree for the first 30 years of its life[, ], it can begin to flower and set seed when only 6 years old, though 10 - 12 years is more normal[, ]. Seedlings have been known to reach a height of 8 metres in three years in a regenerating hardwood forest[].
The tree is generally quite short-lived, growth ceasing almost entirely after about 50 years and trees usually dying before they are 100 years old[, ].
Annual wood production potential is 4 - 20 cubic metres per hectare[].
The flowers are a rich source of nectar and are very fragrant[] with a vanilla-like scent[].
The branches are brittle and very liable to wind damage[]. When plants are grown in rich soils they produce coarse and rank growth which is even more liable to wind damage[, ].
The tree is usually quite shallow rooted, though the roots can range widely, with reports of roots 50 metres away from the main trunk[, ]].
The plants sucker freely and often form dense thickets, the suckers have vicious thorns[]. There are some named varieties selected for their ornamental value[], some of these are thornless[].
Any pruning should be done in late summer in order to reduce the risk of bleeding[].
The leaves are rich in tannin and other substances which inhibit the growth of other plants[]. A very greedy tree, tending to impoverish the soil[].
A very good bee plant[, , , ].
This species is notably resistant to honey fungus[, ].
This species has a symbiotic relationship with certain soil bacteria; these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

Seed - cooked[, , ]. Oily[]. They are boiled and used like peas[]. After boiling the seeds lose their acid taste[]. The seed is about 4mm long and is produced in pods up to 10cm long that contain 4 - 8 seeds[]. A nutritional analysis is available[].

Young seedpods - cooked[]. The pods contain a sweetish pulp that is safe to eat and is relished by small children[]. (This report is quite probably mistaken, having been confused with the honey locust, Gleditsia spp[].)

A strong, narcotic and intoxicating drink is made from the skin of the fruit[].

Piperonal is extracted from the plant, it is used as a vanilla substitute[]. No further details.

All the above entries should be treated with some caution, see the notes at the top of the page regarding toxicity.

Flowers - cooked. A fragrant aroma, they are fried and also used in making jams and pancakes[, , ]. They can also be made into a pleasant drink[, ].

Medicinal

The flowers are antispasmodic, aromatic, diuretic, emollient and laxative[]. They are cooked and eaten for the treatment of eye ailments[]. The flower is said to contain the antitumor compound benzoaldehyde[].

The inner bark and the root bark are emetic, purgative and tonic[, , , ]. The root bark has been chewed to induce vomiting, or held in the mouth to allay toothache[, ], though it is rarely if ever prescribed as a therapeutic agent in Britain[].
The bark of young branches is used in the treatment of fevers and migraine[].

The fruit is narcotic[]. This probably refers to the seedpod.

The leaves are cholagogue and emetic[]. The leaf juice inhibits viruses[].

Agroforestry Uses:

This species has been widely planted for shelterbelts and windbreaks, and is also used to produce woody biomass for energy production[]. It suckers freely, especially if coppiced, and can be used for stabilizing banks etc[, ].
It is used in restoration and rehabilitation projects because its extensive root system holds and stabilizes the soil surface, it sprouts vigorously and prolifically, it increases soil fertility through nitrogen fixation, and it forms a leaf litter that protects the soil. Its main use has been in the rehabilitation of former surface mine sites and for erosion control, but it is also used to rehabilitate contaminated soils, depleted soils, gravel pits, and logged areas, and to stabilize railroad embankments and highway edges[].
The plant is often found as a pioneer on old fields, burned areas, and lands strip-mined for coal[].
The leaves are rich in tannin and other substances which inhibit the growth of other plants[].
The flowers are a rich source of nectar. Honey produced from this nectar is considered to be of high quality and fetches a price premium.

Other Uses

A drying oil is obtained from the seed[, ].

An essential oil is obtained from the flowers. Highly valued, it is used in perfumery[, , ].

A yellow dye is obtained from the bark[]. Robinetin is a strong dyestuff yielding with different mordants different shades similar to those obtained with fisetin, quercetin, and myricetin; with aluminum mordant, it dyes cotton to a brown-orange shade[].

The bark contains tannin, but not in sufficient quantity for utilization[]. On a 10% moisture basis, the bark contains 7.2% tannin and the heartwood of young trees 5.7%[].

The bark is used to make paper and is a substitute for silk and wool[].

The wood is close-grained, exceedingly hard, heavy, very strong (due to a high lignin content), resists shock and is very durable in contact with the soil. It weighs 45lb per cubic foot. It does not shrink much when drying. The wood is used in shipbuilding and for making fence posts, tree nails, flooring, furniture, woodenware etc[, , , , , , , , , , , ]. The wood of Robinia pseudoacacia var. rectissima, the so called 'Long Island' or 'Shipmast' locust, has a greater resistance to decay and wood borers, outlasting other locust posts and stakes by 50 - 100%[].
A very good fuel[, ], but it should be used with caution because it flares up and projects sparks[]. The wood is also used for making charcoal[].

Propagation

Seed - pre-soak for 48 hours in warm water and sow the seed in late winter in a cold frame[]. A short stratification improves germination rates and time[]. Prick out the seedlings into individual pots when they are large enough to handle and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in the following summer. Other reports say that the seed can be sown in an outdoor seedbed in spring[, ]. The seed stores for over 10 years[].
Seed is known to have remained viable in the soil for more than 88 years[].
Suckers taken during the dormant season.