The sweet potato (Ipomoea batatas) is a tropical perennial plant typically cultivated as an annual crop. It is a member of the morning glory family and is primarily grown for its large, starchy storage roots. The plant does produce flowers, but because growers focus on the underground harvest, the blooms often go unnoticed, leading to the misconception that the plant does not bloom.
Sweet Potato Flowers: Appearance and Conditions for Blooming
The flowers of the sweet potato plant are similar to those of the morning glory. They are funnel-shaped and relatively large, usually measuring between 2.5 and 7.0 centimeters in length. The fused petals typically display colors ranging from white to pale pink or lilac, often featuring a darker reddish or purple throat at the center.
Flowering is uncommon in temperate commercial and home gardens. The plant requires a long, warm growing season and specific environmental triggers to initiate sexual reproduction. Sweet potatoes are naturally inclined to flower in tropical and subtropical regions where daylight hours are shorter. A day length of less than 11 hours promotes flower formation. When blooms occur in less-than-ideal climates, they usually appear late in the season, signaling the plant’s maturity.
How Flowering Relates to Tuber Development
The sweet potato is cultivated for its storage roots, which are botanically distinct from the stem tubers of a white potato. The storage root is a thickened, modified adventitious root that grows fleshy to store energy, unlike a true tuber, which is a modified stem.
Photosynthesis produces photosynthates, which the plant must allocate between vegetative growth (vines and leaves), storage roots, and reproductive parts like flowers. Flowering and subsequent seed production represent a diversion of energy toward sexual reproduction, making it unavailable for the bulking of the storage roots.
While flowering does not halt root growth, excessive flower and seed production can represent a measurable loss of potential yield. The appearance of flowers suggests the plant has reached a reproductive maturity cycle. In some cultivars, this can coincide with the peak of the storage root bulking period. However, some research indicates that for certain high-yielding varieties, the presence of flowers does not significantly decrease the final yield.
Cultivating Sweet Potatoes for Maximum Yield
Techniques for maximizing sweet potato harvest focus on channeling photosynthate into the storage roots. Growers must carefully manage nitrogen levels. Excessive nitrogen fertilizer promotes vigorous vine and leaf growth at the expense of root bulking, leading to a diminished root-to-shoot ratio.
Another common practice is “vine lifting,” which prevents the formation of small, unmarketable roots along the nodes of the sprawling vines. If the vines touch moist soil, they may root at the nodes, diverting water and nutrients away from the main underground storage roots. Lifting or cutting the vines prevents these secondary roots from establishing, maintaining focus on the main storage organs.
Optimal harvest time is usually determined by the number of days after planting, typically ranging from 90 to 120 days. The most reliable sign for growers in temperate regions is the yellowing of the leaves and vines, which signals the plant has completed the bulking process. Harvesting must occur before the first frost, as cold temperatures can damage the storage roots and reduce their storage life.