Black locust tree, false acacia

White cluster of black locust flowers

Black locust tree, which is also called false acacia, is a tree species considered invasive.

Black Locust facts, a summary

NameRobinia pseudoacacia
FamilyFabaceae
Type – tree

Height – 30 to 50?feet (10?to?15 meters)
Exposure – full sun
Soil – ordinary

Foliage – deciduous
Flowering – June
Fruit formation – summer

Planting black locust tree

Plant preferably in fall to favor root development before winter and proper regrowth in spring.

If purchased in a container, you can also plant it in spring, taking great care to increase watering at the beginning.

  • Black locust tree loves full sun, that’s where it blooms best.
  • A mix of garden soil and planting soil mix is perfectly suited to grow it.

Pruning and caring for black locust tree, false acacia

No specific pruning is required, but it is important to remove dead or weak branches whenever you notice them.

  • Eliminating dead and diseased branches must be performed regularly.
  • In fall, prune branches that cross over each other and in-growing branches.
  • Snip off suckers in fall, they are quite useless to the tree.

It is also possible to restrict this tree’s growth by pruning it or removing larger branches in fall.

Black locust wood is naturally rot-resistant

Black locust wood terraceBlack locust wood naturally resists rot and insects. It is excellent to make fence posts and other garden items from.

A raised garden bed made from black locust will last decades. Use slabs of black locust to make edges in your raised garden. Unlike regular logs, these won’t need to be replaced every three or four years.

Many stores sell swing sets made from chemically treated wood or metal, but black locust is a perfect alternative.

It’s also possible to build a terrace with black locust. Simply check with the supplier that the wood comes from heartwood, not sapwood.

  • Heartwood is the portion of the trunk that is already older than three or four years.

Drawbacks of black locust wood for building

Black locust has a tendency to warp and twist upon drying.

  • It’s important to layer it well, with slats to keep each board in position.
  • Once drying is complete, it won’t budge.

Also, black locust is slightly more brittle than other woods.

  • Cushion gates with a slab of softer wood or a rubber stop. This will avoid slamming that might crack the wood.
  • When building the terrace, drill holes for screws and nails, especially near board ends.

Learn more about black locust tree

Black locust tree got its scientific name Robinia from its inventor or discoverer Jean Robin, the royal botanist of Henry the IVth of France who planted it for the 1st time Place Dauphine, in Paris, in 1601.

Native to the United States of America, false acacia, which also goes by the common name black locust tree, is a very elegant tree with a balanced bearing. Its hardiness leads it to live a very long life.

  • This fast-growing tree is particularly interesting for the color of its flowers.
  • A great nectar producer, the flowers from this tree will enthrall bees who will come to pollinate it.

Fruits form pods and come from flowers that cluster in very fragrant bunches of white or red when they appear in June.

The green leaves may fall off in fall without even having turned brown. They shimmer and sway and make this tree look alive.

Smaller black locust for small gardens

An interesting variety stays smaller as it grows. It’s called Robinia pseudoacacia ‘Umbraculifera’, because the canopy looks similar to an umbrella!

  • This variety doesn’t grow as tall and tops out at around 20 feet or 6 meters.

Smart tip about false acacia

Upon planting, spread some mulch at the base of the tree and you’ll avoid weed growth!


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Black locust blooming by Valter Cirillo ★ under Pixabay license
Terrace with black locust by Rosalyn & Gaspard Lorthiois, own work
Black locust branch by Melissa McMasters ★ under ? CC BY 2.0