How to Grow Your Own Sweet Potatoes

Sweet potatoes are started from slips. Supermarket tubers may sprout and produce the slips, but like Irish potatoes they are usually treated to prevent sprouting. Disease-free slips from a garden center or mail-order seed company are best, and you'll be sure of your variety.

Plant promptly after the soil is warm, since length of growing season is often the limiting factor. Where the season is long enough, it is recommended planting two weeks after the last frost to insure thoroughly warm soil.

If drainage is poor or plants are overwatered, roots may be elongated and less blocky. To insure good drainage, sweet potatoes normally are planted in 6 to 12-inch ridges, located 3 to 4 ½ feet apart. (However, southern gardeners with fast-draining sandy soil report that ridge planting for them is no great advantage.)

Space the plants 9 to 12 inches apart. Rich soil may allow closer spacing. If spacing is increased much beyond 24 inches, more oversized roots will result, but at the expense of both total yield and quantity.

Being deep-rooted plants often grown in moisture-poor sandy soils, sweet potatoes are usually able to find enough water to survive; but for harvest, they should never have to struggle for water. As a general guide, they will use about 18 inches of water per season.

After your first sweet potato crop, save some of the healthiest tubers to produce your own slips. Cut or split the crown and underground stems of each plant and examine for dark strands or for general darkening of internal tissue, a symptom of stem rot infection. Do not use roots from stems whose internal tissue shows any discoloration, even though the sweet potatoes appear okay. Also examine for surface cracks and black 'eyes', which indicate nematode infestation.

Three potatoes should produce about 24 slips, enough for a 25-foot row and about 60 pounds at harvest. Plant the chosen tubers close together in sand, vermiculite, or perlite hotbeds 5 to 10 weeks before your outdoor planting date. When sprouts reach 9 to 12 inches, cut them off 2 inches above the soil, and set the slips into a good, preferably sterile rooting soil. (I used 4-inch plastic containers filled with a peat/perlite soil mix.) Keep the soil warm (80 to 90 degrees F.) for fast rooting. Sufficient roots should take 10 to 14 days.

Harvesting
Harvest sweet potatoes when slightly immature, if the size is adequate. Otherwise wait until the vines begin to yellow. Try to avoid bruising them when digging as this invites decay. If the leaves are killed by frost, harvest immediately.

Sweet potatoes improve during storage because part of their starch content turns to sugar. For storage, they need to be cured. Let the roots lie exposed for 2 to 3 hours to dry thoroughly, then move them to a humid and warm (85 degrees F.) storage area. After two weeks lower the temperature to 55 degrees F., and they will keep between 8 and 24 weeks.

Beginner's mistakes
Planting too late to take advantage of the full growing season is the most common error. But don't plant to early either. If soil is not at least 50 degrees F., plants will languish, if not perish.

Limited space
If you lack the garden space for sweet potatoes, but would still like to try to grow some, try them in a box at least 12 inches deep and 15 inches wide. Use a light, porous soil mix and place a 4-foot stake in the center to support the vine. Or grow them as a lush, vining houseplant indoors in a bowl or jar.

Varieties
'Jersey Orange', 'Nugget', and 'Nemagold' are the popular dry-fleshed varieties. 'Centennial', 'Porto Rico', and 'Gold Rush' rate high in the list of moist-fleshed kinds.