This is NOT Vinca minor as many believe, but Catharanthus roseus. Both are members of the Apocynaceae family, but they are from different genera. Once classified as Vinca roseus and then changed to Catharanthus, C. roseus is found in nurseries labeled as Vinca or Periwinkle, further confusing those who are looking for V. minor. Moreover, to muddy the waters even more, the C. roseus’ common name is Madagascar Periwinkle. If someone from USDA Zones 9b-11 is looking for a drought tolerant, full sun annual, then C. roseus fits the bill. V. minor does not.
When all other annuals (C. roseus is actually a perennial used as an annual) have succumbed to the heat in Phoenix, the C. roseus is the most widely used substitute for summer mass plantings in the desert, replacing the all those spent petunias and impatiens. It is also used in hanging baskets, borders, and groundcover. Many desert plant purists shudder at the idea of having petunias and periwinkles in desert gardens, but sometimes a shot of color does a person good.
I always plant C. roseus in one of my large wok planters and in several patio containers around July 1. In a sea of beige gravel and dusty, exhausted native plants, the containers full of C. roseus stand out like a sore thumb. Their five-petaled bright flowers and shiny green foliage clash terribly with the desert landscaping, and my inharmonious mixture of colors adds to the effect. Bright rose and lilac, carmine red and dark lavender, all in the same planters, jars the senses even more. I don’t care. It’s a form of summer rebellion.
C. roseus doesn’t need a lot of water. The flowers can get a bit crispy on the edges on an intense summer day, but for the most part, they do best in full sun and just keep on blooming profusely. C. roseus cultivars provide a myriad of colors from which to choose, and they are available from the most upscale nursery all the way to Wal-Mart’s garden center.
This plant, used for centuries in folk medicine to treat various ailments, has proven to have anticancer properties, and compounds in the plant are currently used to make several prescription cancer drugs. Many more pharmaceutical studies for other medicinal uses are taking place. I'm glad to hear that this plant's value goes far beyond that of supporting my summer rebellion.