The names vinca and periwinkle apply both to an evergreen ground cover and to an annual flower, so it's important to know the differences between the two plants if you want success in your garden. Vinca minor, also known as common periwinkle or creeping myrtle, is the ground cover plant often used where grass won't grow. Vinca roseus, the Madagascar or Rose periwinkle, is the annual plant used in sunny flower beds and containers. Both plants are commonly found in garden centers in the spring and summer, but they are used in the garden completely differently.
Growing Annual Periwinkle
Annual periwinkles love the sun and tolerate only very light shade before flowering is affected. Use them for bedding in flower beds, in outdoor containers, or as houseplants for sunny windows. When bedding out, space them 8 to 10 inches apart. They are not particular about soil, and in fact do well in poor soil with low fertilization. Watering is necessary only if plants start to droop. When used in containers, they do best in terra cotta pots which allow for good drainage and air flow; be especially careful not to overwater if grown in plastic pots. They are pest-free if not overwatered. The plants are self-cleaning, so you do not have to dead-head spent flowers, but plants can be pinched back to encourage bushiness if they get too large. They are completely intolerant of frost, so if you want to bring them in for the winter, be sure to move the plants indoors when night temperatures drop down to about 50 degrees. Plants can be propagated by stem cuttings at any time, or you can start from seed three to four months before the last frost date for your area. Periwinkles are easily found in garden centers in late spring.
Annual vinca commonly grows 8 to 12 inches tall, but some varieties can reach a height of 18 inches. Plant spread is typically 12 to 18 inches. Annual vinca produces 1- to 2-inch-diameter flowers above glossy, dark green foliage. Until recent years, the range of flower colors was somewhat limited. Flowers varied from pink to white, often with dark rose or red eyes. Over the past few years, seed companies have developed a large number of new varieties. These new varieties have expanded the color range of annual vinca. Gardeners can select varieties with light blue, pink, salmon, apricot, orchid, raspberry, carmine, and burgundy flowers. Plant breeders have also introduced varieties with trailing and dwarf, upright growth habits.
Annual vinca is easy to grow. It performs best in well-drained soils in sites that receive partial to full sun. Annual vinca possesses excellent heat and drought tolerance, blooming continuously through the intense heat of mid-summer. However, Madagascar periwinkle does not perform well in wet, poorly drained soils or in cool spring weather. Plants turn a sickly yellow green in wet soils or cool spring weather. When choosing a planting site, make sure it has well-drained soil. Also, allow the temperatures to warm nicely before planting in the spring. Annual vinca is free of serious insect and disease pests.
Annual vinca is a low maintenance, relatively trouble-free bedding plant. It blooms from spring until a killing frost in the fall. The removal of faded flowers or deadheading is not necessary. While root and stem rots may occur, these problems can usually be avoided by planting in warm, well-drained soils.
