Annual vinca or periwinkle (Catharanthus roseus) is a summer flowering annual popular in Southern and Midwest gardens (USDA hardiness zones 9-11). When summer’s heat and humidity soars, vincas look their best and bloom the heaviest. Vincas sparkle in containers, in flower beds, or in front borders around building foundations.
Transplants are set out in mid-spring after soils have warmed up and all threats of frost have passed. Vincas grow best in well-drained, organically rich, loamy soil and in full or part sun. Fertilize at planting with a second application in late July. Vincas enjoy occasional watering during prolonged dry spells but avoid sprinkling overhead. Established plants (after 4 to 5 weeks) are rated moderately drought tolerant.
Most modern day cultivars grow short and compact. They vary from 6 to 18 inches in height and spread. An individual flower is composed of five flattened petals attached to a tubular base. A wide range of flower colors include lavender, red, rose, salmon, several shades of pink, and white. Some cultivars exhibit a center eye in the flowers. Old blooms are self-cleaning and never messy. The 1-2 inch long leaves are dark green and glossy.
Most new cultivars contract few, if any, serious insect or disease problems. Plant vincas on an open site with good air circulation to prevent stem and root rot diseases (phytophtora) and bacterial leaf spots. Slugs and snails can occasionally become pesky in wet summers.
Popular vinca series at garden centers are Aztec, Cooler, Cora, Pacifica and Viper. Vincas often self-seed and re-appear in garden beds several years hence.