Sweet potato vine (Ipomoea batatas) is grown around the world both as a food source and merely for its fast-growing, decorative stems and foliage. A tropical plant that dies back to its underground root tubers when a winter frost occurs, it can be left outdoors year round in U.S. Department of Agriculture hardiness zones 8 and warmer. Numerous varieties exist today, providing gardeners options with chartreuse, purple, black or variegated leaves.
Sweet potato vine is native to Central America but is considered "pantropical" today--being grown widespread across all tropical lands the world over. The wild species is more common in regions that rely upon its use for food while the ornate foliage selections find favor in temperate climates for use in annual bedding displays.
A member of the morning glory family, Convolvulaceae, sweet potato vine is not related to true potatoes, which belong to the nightshade family, Solanaceae.
Growing from swollen, fleshy roots called tubers, sweet potato vine is a perennial climbing vine with non-woody, fleshy stems. Reaching lengths of 20 feet or more, the stems normally have a purplish cast to them and support heart-shaped to oval leaves that are entire, toothed or with three lobes. In summer, the plant displays 1-inch sized trumpet-shaped flowers that are lavender to light violet-purple in color. The longer the plant grows, the underground tubers increase in number and size.
Plant sweet potato vines as dormant tubers or containerized young plants when there is no threat of frost at the beginning of the growing season. Choose a soil that is fertile and moist but well-draining. For best growth and health of foliage (and subsequent development of tubers), locate the plant where it will receive at least six hours of sunlight daily. Insufficient light results in leggy stems with fewer leaves and in some varieties causes the colors of leaves to look drab. In hot summer climates or in dry soil conditions, intense sunlight can scorch foliage to look tan or white. Lift tubers after the first fall frost to harvest or store indoors to replant next year, or allow intense winter colds in USDA zones 7 and colder to kill the tubers, and then replant anew next spring.
Few insect pests harm sweet potato vine, but be wary of damage from root weevils in the U.S. gulf states, according to Purdue University. Cutworms may sever tender young stems when plants are first placed outdoors. The other primary, common problem with growing sweet potato is overly wet soil that encourages various fungal rots to infect leaves and stems. When digging tubers, use care as their skin and flesh are easily cut or bruised.