The sweet potato, Ipomoea batatas, is a tropical perennial plant most often cultivated as a warm-season annual root crop. When considering its size, it is important to understand its natural habit is not to grow “tall” in the vertical sense. Instead, the sweet potato plant is a vigorous, ground-covering vine that spreads horizontally across the soil surface. This sprawling growth pattern is characteristic of the morning glory family.
Understanding the Vine: Length and Spread
The vast majority of sweet potato cultivars, including those grown commercially for food production, are vining types that demonstrate rapid, horizontal growth. In a single growing season, a single sweet potato plant can cover a substantial area of garden space. The average length for a mature, healthy vine can range from 6 to 10 feet. Under optimal conditions, particularly in regions with long, warm growing seasons, the vines can extend further, sometimes reaching lengths of 12 to 20 feet. This extensive spread is necessary for the plant’s biology, as the vines will naturally set down roots at the nodes wherever they contact the soil, which then develop into the edible storage roots.
The Difference Between Bush and Vining Varieties
The ultimate size of a sweet potato plant is largely determined by the specific cultivar chosen, categorized into vining and bush types. Vining varieties, often called runners, are the standard type, requiring significant space due to their long, spreading stems (e.g., ‘Beauregard’). In contrast, bush varieties have been selectively bred for a compact, mounding growth habit. These types are ideal for container gardening or small raised beds where space is limited. Compact plants, such as ‘Vardaman’, typically spread only 2 to 3 feet in diameter, creating a dense mound of foliage.
Practical Growth Management: Pruning and Trellising
Gardeners with limited space must actively manage the sprawling growth of vining sweet potatoes through specific techniques.
Trellising
One method is to guide the vines onto a vertical support, or trellis, to grow upward instead of outward. Since sweet potatoes do not possess tendrils, they are not natural climbers and must be manually woven or tied to the trellis structure as they grow. This technique allows the plant to achieve vertical height.
Vine Tipping
Another management technique is pruning, known as “vine tipping,” which involves removing the growing tip of the main vine. This action signals the plant to stop extending in length and promotes the growth of lateral side shoots. Pruning encourages a bushier appearance and redirects the plant’s energy toward the development of underground storage roots. Cut vines should be removed from the garden area to enhance air circulation.
External Factors Determining Final Size
Beyond genetics and management, environmental conditions significantly influence a sweet potato plant’s final size and vigor. The availability of nutrients, particularly nitrogen, profoundly affects vegetative growth. Soils high in nitrogen encourage the plant to put excessive energy into producing lush foliage and long vines, a condition often called “going to vine.” Too much nitrogen can lead to an inverse relationship where vine length increases but the yield of storage roots decreases. Consistent water availability and maximum sunlight also encourage longer runners and greater plant vigor.