Black locust

Profile

Family

Fabaceae

Habit

Tree

Height

25 m

Spread

12 m

Growth

very fast

Lifespan

200 years

First yield

after 6 years

Hardiness

zone 4–9

Shade tolerance

light shade

Soil

Sand, Silt

Soil moisture

very dry – moist

pH

3.5 – 7.5

Synonyms

Scheinakazie

Flowering & harvest

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

Uses

Edible: The seeds are boiled and used in a similar way to peas, losing their sour taste after cooking. Measuring about 4 mm in length, they are found in pods up to 10 cm long, each containing 4-8 seeds. Young seed pods are also suitable for boiling, with sweetish pulp that is safe for consumption, particularly enjoyed by young children. The fruit's skin can produce a potent narcotic and intoxicating effect. Piperonal, extracted from the plant, serves as a vanilla alternative. Boiling the flowers releases a fragrant aroma, often utilized in making jams, pancakes, and delightful beverages.

Medicinal: The plant's flowers have antispasmodic, aromatic, diuretic, emollient, and laxative properties. They are traditionally employed in treating eye ailments. The flower is thought to harbor the antitumor substance benzoaldehyde. The inner bark and root bark possess laxative, emetic, and tonic qualities. The root bark was used for inducing vomiting or alleviating toothache. The fruit exhibits narcotic effects. The leaves display choleretic and emetic characteristics, with the leaf juice showing antiviral properties.

Other uses: A drying oil is obtained from the seeds of the black locust tree. The flowers yield a valuable essential oil for perfumery. The bark produces a yellow dye called robinetin for coloring fabrics. While the bark contains tannin, it is not sufficient for commercial use but is utilized in papermaking and as a silk and wool substitute. These trees are effective in stabilizing riverbanks due to their high water absorption. Black locust wood is durable, hard, heavy, and fine-grained, suitable for shipbuilding, fence posts, tree nails, and flooring. It serves as a good fuel source but requires careful handling due to its tendency to spark. The variety Robinia pseudoacacia var. rectissima, known as 'Long Island' or 'Shipmast' black locust, is notably resistant to rot and wood pests compared to other black locust types.

Growing

The black locust tree thrives in well-drained soil with moderate nutrient levels, also growing in dry, barren areas and tolerating drought and air pollution. It prefers sunny, dry conditions and can withstand rainfall between 61 to 191 cm annually, temperatures of 7.6 to 20.3°C, and a pH range of 6.0 to 7.0. This tree grows rapidly in its initial 30 years, potentially flowering at 6 years but typically at 10-12 years. Its flowers are rich in nectar with a delightful vanilla fragrance. Due to its brittle branches, it is highly vulnerable to wind damage, especially in fertile soils where it grows tall and thin, increasing the risk of wind damage. The plant often spreads through runners with thorns, forming dense thickets. Some ornamental varieties lack thorns. Pruning is recommended in late summer to prevent sap leakage. The leaves of the black locust tree contain tannins and other substances that hinder the growth of surrounding plants, making it a soil-depleting species. It serves as an excellent source of nectar for bees and shows high resistance to honey fungus.

Propagation

Soak seeds in warm water for 48 hours before planting in a cool environment during late winter. A brief stratification process enhances germination speed and success. Once seedlings reach sufficient size, transfer them to a greenhouse for the initial winter. Plant them in their final position the next summer. Alternatively, some sources suggest sowing the seeds directly outdoors in spring. These seeds have a shelf life of more than 10 years. Propagate through cuttings when the plants are dormant.

Notable

Special features: Pioneer plant, which quickly forms large (through root runners) dense stands for 20-30 years, especially on (industrial) brownfield sites; 0.6-1.4 kg honey per tree (flowers 34-59% sugar); stops growing at 30-40 years, by which time the wood is ready for harvest; ~0.4% of German forests; 2100 kWh/rm; 4.1 kWh/kg

Origin & habitat

Eastern North America - Appalachian and Ozark Mountains. Naturalized in .

Mountain forests.

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