All the periwinkles come from Europe, central Asia and northern Africa; and the large periwinkle (Vinca major) is native to France and Italy, and eastward through the Balkans to northern Asia Minor and the western Caucasus. Vinca minor is often called the lesser, or common periwinkle because its leaves and flowers are smaller than the large periwinkle.
Because both are beautiful evergreen perennials that are extremely easy to grow, with attractive, glossy leaves and lovely violet-purple, pale purple or white flowers, they quickly became very popular with gardeners as a groundcover or trailing plant for semi-shade to sun.
In cultivation the plants generally do not bear fruit, and spread vigorously by rooted runners, and this is how they escaped garden cultivation. Both, but especially Vinca major, will often outgrow their original site, and when pruned or dug out by the roots and disposed of with the garden refuse, these remarkable plants will start rooting wherever they are discarded and will quickly colonize a whole new area.
Periwinkles grow throughout South Africa but the large periwinkle (Vinca major) is particularly problematic in KwaZulu-Natal, and both the Eastern and Western Cape. A variegated form is also available which has a similar, invasive habit. And, although sterile cultivars and Vinca minor are not listed, I believe we should exercise caution when growing these too, as they also spread via rooted runners, and in other areas of the world people are debating their invasiveness.
Vinca major 'Variegata' Picture courtesy Leonora Ellie Enking from flickrSo what does this mean for you if you have Vinca major growing in your small garden or even on a large property or farm? Category 1b invasive species in South Africa require compulsory control as part of an invasive species control process. These plants are deemed to have such a high invasive potential that infestations can qualify to be placed under a government sponsored invasive species management programme. Wherever possible, the plants must be removed and destroyed responsibly, and no permits will be issued to keep these species.
You can spot the large periwinkle easily in the wild because it grows so rampantly, and especially in moist, shaded areas, along forest edges, streambanks and roadsides, and where moisture is sufficient it will also thrive in full sun. It can grow so rampantly that the trailing stems will form dense mats of vegetation - about half a metre high, completely covering the surrounding plants, blocking out the light and competing for nutrients. This completely changes the habitat and ecosystem, and since infestations often occur in fragile environments like forests and alongside streams, this has serious implications for our biodiversity.
No herbicides are registered specifically for use on periwinkle, but a systemic herbicide sprayed on the leaves may kill the plants. Small infestations can be removed by hand-pulling, but ensure that all parts of the stems are carefully removed since any fragments will merely regrow. I never found any advice on how to safely dispose of the plants, but I would imagine that allowing them to dry out and then burning them would be good, or digging a very deep trench and burying them so deep that they cannot sprout and become compost is good?
The leaves contain toxins and are generally not browsed by animals. Gardeners and farmers are strongly urged to remove these plants, and to replace them with some of our most beautiful indigenous plants such as the Bush Violets (Barleria obtusa and Barleria repens), or for more sunny sites our gorgeous African Daisies (Dimorphotheca)