Robinia pseudoacacia Seeds | Black Locust
LATIN NAME: Robinia pseudoacacia
COMMON NAME: Black Locust
Plant Profile
Black locust is a fast-growing tree of the eastern United States, now planted and naturalised far beyond its native range. It reaches ten to twenty-five metres, with a straight, deeply furrowed trunk, compound leaves of many oval leaflets and pairs of stout spines at the base of each leaf. In late spring it hangs out long clusters of white, pea-like flowers that smell of orange blossom and are loud with bees. Flat brown pods follow and stay on the tree into winter. It spreads aggressively by root suckers, forming thickets that crowd out everything else, which is why it is classed as invasive in much of Europe. The wood is exceptionally hard, durable in soil and fast to produce, and it burns well.
Science & Biotechnology
Black locust fixes nitrogen through root nodules containing Rhizobium, and it does so at a rate high enough to change the soil beneath it, raising nitrogen and altering the plant community. That trait makes it valuable for mine spoil and degraded ground and a problem in nutrient-poor habitats where it favours nitrophilous weeds. The wood’s durability comes from robinetin and dihydrorobinetin, flavonoids that inhibit fungal decay and give the heartwood its greenish-yellow colour; tests place it among the most rot-resistant woods of the temperate zone. The tree also contains the toxic lectin robin and the alkaloid robinine in bark, leaves and seeds, and poisoning of horses and cattle is well documented. Seed coats are impermeable, and germination in the wild follows fire or abrasion, which is why stands appear after disturbance.
Uses & Benefits
The timber is the main economic product: fence posts that last fifty years, boat timbers, decking and firewood of high density. It is also planted for erosion control, for windbreaks and for reclaiming coal spoil, and it is a major honey plant in eastern Europe, where acacia honey is a commodity in its own right. The flowers are edible and are fried in fritters or steeped for tea in parts of Italy and the Balkans, and they are the only part of the plant that is safe to eat. In the garden it is a tree for a poor, dry site where something has to grow fast, but its suckering habit makes it unsuitable for a small plot. It is also useful as a nurse tree for more demanding species.
Growing from Seed
The seed coat is hard and needs scarifying. Pour near-boiling water over the seed and leave it to soak for twenty-four hours, then sow the swollen seeds and discard the rest. Sow one centimetre deep in a free-draining mix and keep at twenty degrees; germination takes one to three weeks. The seedlings grow very fast and can reach a metre in the first season. Pot on or plant out in autumn into any well-drained soil in full sun. Water for the first summer only. Be careful about siting: the tree suckers widely from the roots, and cutting it down tends to make the thicket denser. Keep it away from septic lines, paving and small gardens.
Our Take
The fastest, hardest, most invasive tree on this list. Plant it where a thicket is useful, never in a small garden.
Related Reading
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