ALIEN AUDIT (2): JACARANDA

Jacaranda

Jacaranda trees have been growing in South Africa for so long that most people regard them as being indigenous. That they are not, although the Jacaranda has been a beloved naturalised plant citizen, from the time it was introduced from South America in the early nineteenth century. Jacarandas (Jacaranda mimosifolia) have been planted by municipalities all over the country since then, thanks to their beautiful mauve flowers that more than meet the criteria for ornamental purposes. The most prolific plantings are surely in Pretoria, where it has been estimated that over 70 000 Jacarandas are growing – no wonder it is known throughout the country as Jacaranda City!

A number of these trees grew on the campus of the then University of Natal in Pietermaritzburg, covering the lawns and paths with a mauve carpet when I was a student. The trees flower from September to November – the periods differ slightly in different parts of the country. Certainly it was an urban myth in my student days that if you had not started preparing for the end-of-year examinations by the time the Jacarandas blossomed, your chances of getting a good pass were diminished. On the other hand … if a blossom fell on your head, you were bound to be fortunate in one way or another! The flowering season starts later in the Eastern Cape and so that myth would hold no water for the Rhodes University students in Grahamstown, for example.

Jacaranda blossom

Why then would this beautiful tree fall foul of the alien audit of my garden? Some years ago the government listed the Jacaranda as an invasive species that required eradication – can you imagine the uproar that resulted in places such as Pretoria? This is because they tend to invade river banks, rocky ridges and gorges in some parts of the country such as Limpopo, KwaZulu-Natal, Gauteng and Mpumalanga. The classification is in line with a countrywide decision to get rid of invasive aliens (this includes some species of eucalyptus as well as black wattle) in order to improve the natural supply of water from rivers and other wetlands.

A compromise was reached: although Jacarandas are still regarded as invaders, existing ones do not have to be eradicated. No further trees may be planted though and so they are no longer available at nurseries. We have some Jacaranda trees growing on the verge and in all the years we have lived here I have not found a single seedling growing in my garden. I commented last month on the exquisite carpet of mauve flowers covering the pavements and streets in the early morning. The reprieve on total eradication is appreciated.

Advertisements

ALIEN AUDIT (1): SWORD FERN

For years now, South African gardeners have been urged to rid their gardens of invasive alien plants. Ironically, many of these plants were recommended to us as ‘fast growers’ by the local nursery when we started our first garden from scratch in Pietermaritzburg many years ago. Times have changed, along with a broader understanding of how some of the more aggressively spreading alien plants can displace our indigenous vegetation. The former tend to grow well because they are not prey to local insects or diseases.

While we can look back with satisfaction at all the indigenous trees we have planted in our present garden over the years, and having got rid of an infestation of Lantana spp. – as attractive as they are – a recent ‘audit’ shows that we still have a way to go. Many of these plants were either inherited with the garden or have arrived uninvited. In this occasional series I will highlight some of the alien visitors we still need to see the back of.

The first is an old ornamental stand-by in gardens all over the country, the hardy Sword Fern (Nephrolepsis exaltata).

sword fern

Swathes of Sword Ferns have commonly been used to fill empty spaces where ‘nothing else will grow’ and have even been given pride of place in large pots to provide a flush of green on hot verandas. If you look around, many city buildings have Sword Ferns growing in neglected cracks and they feather damp patches in old walls and outbuildings. Sword Ferns have been popular because they are tough and apparently drought-resistant – qualities that have endeared them to even the most lacklustre gardeners.

sword fern

The Sword Fern is an import from North and Central America, however, and is difficult to get rid of once it takes hold of one’s garden. I can attest that the small patch we inherited has spread vigorously, almost taking over the area where the infestation began and in doing so has crowded out some of the plants that were growing there. Try pulling them out and you are met with stolons and tubers that break off and get left behind to spawn another colony while your back is turned! Apart from the afore-mentioned, Sword Ferns are also spread by the dispersal of their wind-borne spores.

sword fern