Robinia pseudoacacia
Black locust, false acacia, acacia (incorrectly), carob tree, bastard locust: imported from North America at the beginning of the 17th century by Jean Robin, gardener to Henry IV, it gave its name to the genus. One of the trees he planted in Paris is still alive in Square René-Viviani — it is the oldest tree in the capital. It is also the tree behind the famous “acacia honey,” which therefore has nothing to do with true acacias.
Characteristics:
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Major nectar-producing bloom: long, highly fragrant white clusters in May–June, the source of acacia honey.
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Very rapid growth: it reaches 20 to 30 metres and produces usable wood in just a few years.
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Rot-resistant wood: naturally resistant to rot without any treatment, it is the European alternative to exotic woods.
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Nitrogen fixer: as a legume, it enriches the poor soils where it becomes established.
Precautions — read before planting:
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Invasive exotic species: black locust spreads very vigorously through root suckers and rapidly colonises open habitats. It appears on the lists of species to monitor in several French regions. Do not plant it near natural areas, meadows or wild edges, and plan to install a rhizome barrier or regularly monitor root suckers if you plant it in the garden.
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Toxicity: the bark, leaves, roots and seeds are toxic if swallowed. Only the flowers are edible (in fritters). Keep the seeds out of the reach of children and pets.
- Its branches bear sharp thorns: gloves are essential when pruning.
Sowing advice:
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Exposure: full sun, for rapid growth.
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Soil: virtually all types, including poor, sandy, stony or degraded soils, provided they are well drained. As a nitrogen fixer, it needs no fertiliser and thrives where other species fail. It mainly dislikes waterlogged soils.
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Method: the seed coat is extremely hard. Lightly scarify the seeds with a file, or soak them in very hot (not boiling) water for 12 to 24 hours: the seeds that swell are ready to sow; repeat the process for the others. Cold stratification can complement the treatment. Then sow in spring in a deep pot.
Planting advice:
- Choose the permanent location carefully, taking into account its mature spread and root suckering: keep it away from property boundaries, pipes and natural areas.
- It reaches its full potential in short-rotation coppice for producing stakes: cut every 5 to 10 years, it regrows vigorously from the stump.
Care advice:
- Water moderately during the growth phase; afterward it tolerates drought very well.
- Monitor and remove root suckers every year: this is the key to keeping it in its place.
Benefits for biodiversity:
- Its bloom is among the most nectar-rich there is: a single day of nectar flow can provide several kilograms of honey per hive, making it a key tree for beekeepers.
- Like all legumes, it fixes atmospheric nitrogen and restores poor or eroded soils — see the basics of living soil.
- Its vigour, an advantage in controlled planting, is also what makes it problematic in natural habitats: reserve it for land where you can contain it.
Uses:
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Wood: rot-resistant without treatment, it is ideal for fence posts, outdoor structures, decking and garden furniture — a local alternative to exotic woods.
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Beekeeping: a benchmark honey tree in France.
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Soil restoration: planting on degraded land, embankments and former quarries, where it fixes nitrogen and stabilises the ground.
- Its flowers are eaten in fritters, a traditional countryside recipe.
Symbolism:
Symbolising vigour and adaptability, black locust embodies the ability to thrive on the most barren land. The tree planted by Jean Robin in 1601 is also a living witness to four centuries of Parisian history.
Harvesting your own seeds:
Its flat pods turn brown in autumn and often remain on the tree throughout the winter. Harvest them when dry, open them and store the seeds in a dry place: their hard seed coats give them a shelf life of several years. Clearly label the packet, as these seeds are toxic. See storing your seeds.
Commitment to Quality: at SemiSauvage - Permaculture, we grow and select our seeds with respect for living organisms as our guiding principle. Based near the Auvergne Volcanoes, we choose reproducible, non-hybrid varieties, tested for their germination rate, sorted and carefully packaged, without any chemical treatment. Our conviction: to restore gardeners’ ability to sow again, year after year, seeds that truly belong to them.
Sales reserved for knowledgeable amateur gardeners capable of planting this tree in a controlled setting.
