Friday, October 30, 2009

Alien Watch

Invaders from Central and South America

- Carol Tissiman -

We’ve chosen two plants to highlight this month: a popular cactus and a tree.

Many keen gardeners have enthused about spiny and very hardy cactus plants – none of which are indigenous to South Africa. All these plants have either been brought in as ornaments, hedging and one of the cactus family plants came in as food or fodder. While prickly pair crops have been successful in the past, the newer hybrid version is non-invasive and has proved a better alternative. Sadly, the dear little miniatures sold in many retail outlets turn into major problems in gardens and particularly, our veld.

A good example of these invaders can be found along Christina de Wit Street on the way out of town on the right hand side, where they have invaded the lower slopes of the koppie. The problem with the cactus plant is that when bits break off, they quickly root themselves again and simply take over more area.

The opuntia imbricate (imvricate prickly pear, kabelturksvy) is a good example. This one has showy purple-red flowers, and yellow succulent berries. Take care to wear thick gloves if handling, as the spines contain a skin irritant. Best method is to inject the green stems with a strong herbicide. Dead branches should be carefully collected and burned.

We suggest a great alternative to this would be a euphorbia, of which several varieties are available for this area, which grow in similar conditions and provide a similar architectural effect in the garden.

This month’s tree alien is a popular evergreen shade tree, Shinus terebinthifolius (Brazilian pepper, Brasiliaanse peperboom). This tree has been commonly planted in gardens, and now invades woodland, coastal bush, roadsides and riverbanks. It was declared a Category 1 invader in KZN and 3 in the rest of the country, while its status is under review to be changed to category 1 through-out. The leaves are dark and leathery, flowers creamy-white and small on both male and female trees, fruits are bright red like pepper corns. Perhaps the only benefit this fast growing and very invasive tree has been to provide shade, hedges, and pollen for bees to make honey. For those who suffer from hay fever, and any respiratory problems, keep the Brazilian pepper out of your garden!

We suggest some great alternative fast-growing trees would be a dodonea viscosa (sand olive, yster bos) which is hardy or even harpaphyllum caffrum (wild plum, wildepruim) which will require more water in its early life.

(Source: Lesley Henderson, Alien Weeds and Invasive Plants)

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