Are Convolvulus Plants Perennials?
If you love to grow flowering plants, you have many different varieties from which to choose. Plants in the genus Convolvulus (Convolvulus spp.) can be fun and rewarding to grow, making good choices for a flowering border or, in some cases, useful as ground covers. These plants grow as perennials in areas with relatively warm winters but do well as annuals elsewhere.
Cultivated plants in genus Convolvulus are sensitive to long periods of frost. The native Mediterranean plant called bindweed (Convolvulus tricolor) grows as a perennial in U.S. Department of Agriculture plant hardiness zones 9 through 11, where it reaches a height of about 16 inches and has attractive blue flowers with yellow centers. Another plant called silverbush (Convolvulus cneorum) is a bit more hardy and grows in USDA zones 8 through 10. It's also called bush morning glory because of its trumpet-shaped white flowers that resemble morning glory blossoms and its growth as a 1- to 2-foot-tall bush. Ground morning glory (Convolvulus sabatius) is a perennial in USDA zones 7 through 9 and can tolerate subfreezing temperatures for short times. Like the native bindweed plant, this variety has bright blue flowers and makes a good ground cover, growing only about 1 foot tall.
Use as Annuals
These plants are generally fast growers that also make good annual plants. They can be sited in the garden in early spring and bloom quickly, setting buds shortly after stems and foliage appear. For example, silverbush blooms in early summer, with flowers lasting through August. All types prefer a spot in full sun but can tolerate some light shade for part of the day. In areas with hot summer afternoons, an ideal location gets morning sun, followed by light afternoon shade. Although the plants do well as annuals, they sometimes die back to ground level when cold winter arrives. However, they revive from their roots in spring if winter cold isn't too severe.
All cultivated plants in the genus Convolvulus are quite tolerant of dry conditions, although giving a plant regular waterings after planting helps it get off to a good start. Once established, the plants survive drought especially well. They also do well in coastal locations, where both soil and air can be high in salt, and can tolerate any type of soil, provided it's well-drained and doesn't stay soggy after watering or rainfall. If your soil has a high clay content and holds water, adding sand at planting can increase its drainage and help these plants grow well.
If you live in the colder portion of these plants' range, you can increase the likelihood that your plant will survive winter by mulching it well. Add a 2- to 3-inch layer of organic mulch around its root zone in fall, which helps protect the plant from cold spells. As winter approaches, keep the plant well-watered to increase its ability to survive cold. You could also grow the plant in a container, or dig up a garden-grown plant and transplant into a pot, moving it indoors during winter. Indoors, it needs a bright spot such as near a south- or west-facing window, but it should be sheltered from cold drafts.