Cultivating Sweet Potatoes

HISTORY

While the sweet potato originated in the tropical and subtropical areas of meso and South America, the remarkable journey it made around the world and into the diets of many cultures would impress even the most well-heeled jetsetter. While it is often interchangeable with potatoes in culinary applications, the sweet potato tuber, also called kumara, thrives in warm, humid climates where it is difficult to grow the true potato.

Sweet potatoes are thought to have been domesticated from I. trifada, which is native from Mexico down to Venezuela, and were carried around the world to the South Pacific islands, Egypt, India, New Zealand, Sri Lanka, Japan, and China where it reportedly arrived around the end of the 16^th century.  They reached southern Europe by the early 16^th century – before the arrival of the true potato.

The Taino Indians of the Greater Antilles and Bahamas named the sweet potato batata. The  Spanish gave the same name to the Andean tuber or true potato, thus both tubers ultimately became known as potato, with the sweeter, tropical plant later used termed the ‘sweet potato’ to distinguish the two markedly different varieties of tuber.

Like the potato, there are many varieties of sweet potato developed for various types of food preparation around the world.  Cultivars high in starch are sweeter and commonly used for making crisped chips, candying and roasting, while other varieties are better suited for soups,  stews and mashing.

CULTIVATION

Sweet potato typically grows as a trailing vine, but semi trailing and even compact bush types have been developed to make the most of limited garden space. They thrive in warm weather and when planted well after danger of frost, quickly shade out weeds as the season progresses.  

Outside the tropics, sweet potatoes are commonly grown from rooted shoot cuttings called slips, which are widely available from garden centers and reputable mail order suppliers, and are a fast, reliable method for establishing a backyard sweet potato crop. Reputable mail order suppliers, like Southern Exposure Seed Exchange, for example, often sell certified organic sweet potato slips that are well adapted for a specific region of the country.

Sweet potatoes prefer loose, well drained soil, and a raised planting area that’s 12” deep or more, filled with a light organic soil blend will ensure your sweet potatoes have room to fully develop.

Transplant slips in the garden 3” deep, 10”-18” apart in rows at least 3’ apart. This spacing is crucial to allow room for the sprawling vines to develop. Slips should be transplanted in the evening, and watered in well, with the soil kept moist for the first several days as the plants get established.

Once established, sweet potatoes can perform well with little water or fertilization, but irrigation and even moisture can help prevent splitting and cracks, and side dressing the plants with compost will improve both size and overall yield.

HARVESTING

Sweet potatoes typically require between 90 and 120 days to reach maturity, depending on the variety, and the best way to check the size of your crop is simply to dig one of the plants after the recommended growing time has passed. If they’re still a little small, wait another week or so and try again. It’s best to harvest on a sunny day when the soil is relatively dry. Begin by pulling the vines aside so you can see where to dig, and using a spading fork, start about 12” away from the main stem of the plant, digging 6” straight down, then angle toward the center of the plant and lift the potatoes up out of the ground. Separate the sweet potatoes and dry in the sun for about an hour, handling them gently to avoid bruising.  While they’ll continue growing if left in the ground past the recommended growing period, growth will slow as the weather cools, and for optimum storage quality, they should be harvested before the soil temperature drops below 55 degrees.  

Don’t’ want to wait four months to enjoy your sweet potato patch? The tender shoots and leaves of the sweet potato vine are also commonly harvested,  and used as cooking greens much like spinach ; chopped, steamed, sautéed, etc.  Just be sure to leave enough of the vines and shoots above ground to ensure a vigorous plant that produces a good crop of sweet potatoes below ground later in the season.

CURING & STORAGE

Curing improves the sweetness and storage quality of sweet potatoes, and also allows for the healing of scratches and any other damage. After harvesting, allow the sweet potatoes to dry completely, then  shake off any excess soil.  Never wash sweet potatoes before curing.  Cure them by keeping at 85 degrees and 90% relative humidity for a week to ten days.  A space heater can be helpful in creating these conditions.  For long term storage, choose firm, well shaped potatoes with even coloring and free of bruises.  Small or damaged sweet potatoes can always be washed and used right away. Store cured sweet potatoes in a cool, dry place away from light. Properly cured sweet potatoes will store between 5 and 12 months unrefrigerated.

GROW YOUR OWN SLIPS NEXT YEAR

Start about 8 weeks before planting time, by selecting 1.5” diameter sweet potatoes from high yielding hills. First soak the sweet potatoes in water for two hours, then place them in a pot or flat half filled with soil or compost.  Cover the  sweet potato with another two inches of soil and keep evenly moist in a warm, sunny place indoors. When it’s time to plant, cut the slips about an inch away from the ‘mother potato’ to avoid transferring any diseases. Slips should be about 8-10” long when they’re cut and planted.

Ready to get started on your own sweet potato crop? We recommend the high quality sweet potato slips offered by these reputable suppliers :

Sow True Seed Co.

Southern Exposure Seed Exchange