By Josie Borlongan, Garden Guides Contributor
About Sweet Potato
Sweet potatoes are tender perennials grown as annuals. They have trailing stems that can grow up to 10 feet (3 m) or more if not pruned. These tubers bear alternate heart-shaped flowers. The tubers are eaten and the leaves are cooked, much like spinach leaves. Commonly referred to as yam in error, a sweet potato has long, tapered, edible tuberous roots. It has a smooth skin with color ranging from red, purple, brown and white. The fresh color ranges from white through yellow, orange and purple. Sweet potatoes are tropical and subtropical and require a temperature ranging from 75 to 79 degrees F (24 to 26 degrees C).
In warm climates, sweet potatoes need a sunny site; in temperate climates they should be covered. However, this condition may yield tubers that are smaller. Most cultivars are short days, where plants grow and seed only if the day's length is less than 12 hours. The soil must be well drained and highly fertile with a pH of 5.5 to 6.5 and medium-to-high nitrogen levels are required, using fertilizer with 21 percent N content should be between approximately 1.5 to 2 oz. per square yard (45 to 55 g per square meter) and 2.5 to 3.5 oz. per square yard (70 to 100 g per square meter).
Sweet potatoes are also grown as ornamental plants. The genus Ipomoea includes several garden flowers called morning glories. These yellow or orange tubers are elongated and taper to a point at the end. There are paler yellow sweet potatoes that have pale yellow flesh but are not as sweet as the darker yellow ones (commonly mistaken as yams) that have thicker flesh and reddish green skin with orange tinge.
Choosing a Variety
The recommended sweet potato varieties are orange-fleshed, such as Beauregard, Centennial, Georgia Jet and Vardaman, as well as white-fleshed, such as Jewel and White Yam.
In tropical or subtropical areas, sweet potatoes are planted at the start of the rainy season. Sweet potatoes should be planted during springtime if you live in warm and temperate climates. These tubers should be planted after the frost in cooler climates. When planting the tubers, create raised ridges about 30 inches (75 cm) apart, then plant the tubers 2 to 3 inches (5 to 7 cm) deep in the ridge. Ensure that there is enough spacing around 10 to 12 inches (25 to 30 cm) apart. You can plant seeds indoors using trays and pots sized between 8 to 10 inches at warm room temperature of 75 degrees F (24 degrees C). You can then transplant them outside once the stem reaches 4 to 6 inches (10 to 15 cm) high and hardened.
You can also grow sweet potatoes from stem cuttings by selecting healthy and vigorous shoots that have been cut off from the parent plant using pruners. Remove the lower leaves and trim each shoot below a node to 8 to 10 inches (20 to 25 cm). Insert in pots then cover.
Sweet potatoes need to be watered regularly. Weeds need to be taken care of immediately to avoid hindering growth. Use mulch to conserve moisture. You can train shoots to spread around the plant. Fertilize using a general purpose fertilizer at two- to three-week intervals until the tubers have formed. Protect the plants from strong winds by placing stakes around the plants and wrapping plastic around.
Watch out for pests, such as aphids, caterpillars, root-knot nematodes, fungal leaf spots, Fusarium wilt, Southern blight and other viruses that can attack the plants when grown outdoors causing bacterial and fungal diseases that are characterized by rotting. Whiteflies, thrips and spider mites are common problems when growing sweet potatoes under cover.
Harvesting and Storage
Sweet potatoes can be harvested after 12 to 16 weeks of planting or when the leaves and stems have turned yellow. Crops from seeds are ready around 20 weeks later. Use a gardening fork to lift the tubers. Ensure that you lift gently without damaging them. Cure the harvested sweet potatoes for four to seven days at temperatures between 82 to 86 degrees F (28 to 30 degrees C) with relative humidity of 85 to 90 percent before storing at 50 to 59 degrees F (10 to 15 degrees C) in shallow trays.