By Bob and Ena Mcintyre Garden Route Branch

Weeds in our Area (Part Sixteen )

By Bob and Ena McIntyre – Garden Route Branch.

Plectranthus comosus (Woolly Plectranthus) and

Nephrolepis exaltata (sword fern).

Many plants that have become problem plants in South Africa were introduced as interesting or attractive garden subjects. Many have subsequently ‘escaped’, and with no natural enemies are proliferating and transforming landscapes to the detriment of our environment. Some of the popular exotic garden species have been classed as Category Three invaders. This classification provides that plants in existence on 30 March 2001 may be retained in a garden provided they are not within 30 meters of the 1:50 year flood line of any watercourse and that the owner of the land on which they occur is responsible for controlling their spread. No new plantings may take place. Ease of cultivation has been the quality that has made many Category Three plants very popular. Two examples very common in our area are Plectranthus comosus (Woolly Plectranthus) and Nephrolepis exaltata (sword fern).

Plectranthus comosus (Woolly Plectranthus) is a large vigorous shrub that reaches up to 3m in height with densely woolly stems and large light green leaves. The leaves are usually more than 100mm long and 47mm wide. The flowers are blue or mauve up to 20mm long in a terminal spike-like raceme approx 200-300mm long. This plant can be found invading forest margins, roadsides and moist areas in our indigenous forests. The plant is very robust - coppices and readily roots from any node of a cut branch in contact with soil. A stem of the Woolly Plectranthus, about 600mm long and about 60mm in diameter continued to produce green leaves and small air roots for well over a year simply left standing on a concrete slab. We assume that the section survived on moisture drawn from the air during this time. When eradicating a plant, remove the stump roots and all or treat the cut stump with a herbicide such as Chopper at 3% mix. Shredding or burning should be used to destroy all parts of the plant.

Nephrolepis exaltata (sword fern) is a major transformer and crowds out any indigenous plant species. It is a stiff and very hardy evergreen fern up to 1m high that form extensive colonies by means of stolons and tubers. The plant also spreads by wind-borne spoor. The recommended means of eradication is extraction and to destroy all parts of the extracted plants. Follow-up is essential to remove any re-growth and missed tubers. No herbicide is registered for the control of Nephrolepis exaltata.