The black wattle tree is a dangerous alien invader.  It is an evergreen tree and can grow up to 30 meters in height.

These intruders were introduced into South Africa between 1858 and 1864.  it is not sure whether the first black wattle trees were planted in the Cape Town Botanical Gardens (1858) as decorative trees or in the present-day KwaZulu-Natal near Camperdown (1864) as commercial trees. 

Due to its high tannin content (around 30%), the black wattle was planted commercially to be used in tanning leather.  The wood was also used for firewood, building materials and as wood chips.

Unfortunately these exotic trees – native to South-East Australia – have started growing profusely outside commercial plantations, along water courses and roads.  They tend to grow in dense copses, especially after a fire has passed through the area.  Because these trees were planted outside of their natural habitat, they do not have to contend with their natural enemies, which control their numbers.  These trees steal water, nutrients and light from our indigenous plants and trees, and therefore replace our native flora.  Especially our fynbos areas are threatened by the black wattle.

The black wattle has been declared an invader plant throughout South Africa, except in areas where they are commercially planted.    These commercially planted trees should be monitored, however, and be prevented from spreading out of the plantations.

Black wattles reproduce by their seeds, which can remain dormant, yet fertile, for a period of 50 to 80 years.  These seeds do not germinate immediately, and can gather quite thickly under the trees.  Should a wild fire spread through the trees, all of the seeds will germinate simultaneously, which causes an even bigger problem.

These trees also re-sprout rather heartily, adding to the level of difficulty in getting rid of them.  Should you fell a wattle tree, you must ensure that you treat the stump with a herbicide, to prevent it from re-sprouting.  As these trees normally flourish along water courses, you need to ensure that you use a registered herbicide and definitely steer clear of diesel-based products, as this will contaminate the water course.

If the trees are still young – seedlings and saplings – you can pull them out by hand, when the soil is wet.  However, if there are very many of them, it is best to use chemical control measures, as extreme soil disturbance will also promote the germination of seeds.

The bottom line is that you should never plant a black wattle in your garden and you should do your share in terminating these plants responsibly to enhance the growth of our indigenous flora.

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