Weed of the Month: Black locust (Robinia pseudoacacia)

The November weed of the month is Black Locust – Robinia pseudoacacia

Ever heard of a tree that just won’t take a hint? Meet Black locust! While this tree has been a beloved addition to streetscapes and gardens, it’s now on the prohibited list in the Port Macquarie region. Once appreciated for its ornamental charm, Black locust is now proving to be a hidden nuisance, with a few serious downsides that have turned it from popular to problematic.

What’s the Big Deal with Black Locust?

Black locust goes by many names – Golden Robinia, False Acacia, Robinia ‘inermis’, ‘frisia’ – and despite its attractive varieties, they all come with a common issue: a relentless root system. This tree is a master of survival, using root suckers to respond to any stress or damage by sending up thorny new growth. These suckers are more than just a minor inconvenience. If left unchecked, they form dense, impenetrable thickets that can quickly turn hazardous for people, pets, livestock, and native animals alike.

Here’s the kicker: suckers can keep sprouting for years, even after the main tree is long gone. And they don’t just stay put – they can emerge as far as 50 meters from the original tree! In urban spaces, this means that Black locust can creep into neighboring yards, causing property disputes and hefty removal costs. Not only that, but all parts of this plant are toxic, posing a risk to people and pets.

How to Spot a Black Locust

Size

Often 5-15m in gardens, but capable of reaching up to 25m.

Leaves

11-21 paired, oval-shaped leaflets with a single leaflet at the end. The foliage is deep green, turning golden in autumn.

Flowers & Seeds

Fragrant white, pea-like blossoms in clusters, followed by leathery seed pods around 5cm long.

Stems

Smooth, brown bark on young trees, with sharp, paired spines along the stems.

Need to Remove Black Locust? Here’s What You Should Know

Dealing with Black locust removal is a job for the experts! Even minor disturbances to the tree or its roots can trigger those pesky suckers, making removal a careful and calculated task.

For more detailed information on Black locust, refer to NSW WeedWise, if you think you may need to address Black locust on your property, reach out to Council’s Biosecurity Officer for the best treatment options.

Image credit: Port Macquarie-Hastings Council & NSW WeedWise.

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