Learn to grow a sweet potato

Regardless of your planting location, growth may seem slow at first as the slips take root. Then, toward midsummer, the vines will grow like crazy.

Weed thoroughly (but carefully, so as not to damage the young, shallow roots) as the vines begin to spread. The vines may try to root into the bare ground. If you wish, you can lift them to slightly dislodge any roots that may have formed, but it's not critical to do so. Come August, your sweet potato tubers will be growing and swelling.

Harvest and storage
Sweet potato growth slows when soil temperature falls below 18°C . When the vines turn black after the first frost, harvest your potatoes immediately. Dig them out carefully because the skins are susceptible to bruises and cuts. Leave them outside on the ground to dry for several hours, then brush off the dirt and gently transfer to a box lined with newspaper. Leave them in a warm (27°C), humid place for two weeks. Proper curing is essential to create a layer of suberin (a waxy substance that keeps moisture in and helps to heal any nicks or cracks in the skin). Then store at room temperature for up to a year. “[The flavour of] a well-grown sweet potato actually improves in storage,” says Wingate. “The starches gradually convert to sugar.”

Let it slip
Here's how to grow your own slips:
Stick toothpicks around the middle of a sweet potato and suspend it in a jar (or sturdy glass) of water, submerging the bottom half of the tuber (the end with remnants of previous stems—often the wider end, depending on the veggie's shape—should point up). After about a month, you should have several slips about 20 centimetres long. Remove them with a knife or simply by giving them a twist.

Another way to grow slips is to place several sweet potatoes in a bed of sand covered with a moist layer of more sand five centi­metres thick. Once the shoots start to grow, add an additional 2.5 centimetres of sand, keeping it moist but not waterlogged and between 15 and 27°C. Slips should reach 20 centimetres in about six weeks.

(Keep in mind, however, that supermarket-bought sweet potatoes may not produce slips if they have been kept in cold storage—below 10°C.)

Yam, not! Are, too!
So, are sweet potatoes and yams the same thing? No...and yes. True yams (Dioscorea), which are large, starchy tubers, grow only in tropical and subtropical climates. It's thought that African slaves in the southern U.S. began calling sweet potatoes nyami, which was the name for yams in their homeland. To add to the confusion, some American growers of moist, orange-fleshed sweet potatoes have recently begun referring to them as yams to distinguish them from sweet potato cultivars with a whiter, mealier flesh. The latest wrinkle: a number of sweet potato growers are starting to spell the name “sweetpotatoes.”

Grower Greg Wingate of Mapple Farm
in New Brunswick, who ships slips throughout Canada and the U.S., notes that on arrival, slips may look a little sad—yellowed or browned—but they'll soon perk up if properly cared for. If you can't plant them immediately, place the slips in a clear jar and cover the rooted area with room-temperature water. You can also plant them temporarily in a seed flat and keep them in a warm place with light until you're ready to go.

Canadian gardeners are far away from the sweet potato pests and diseases that traditionally affect growers in the rest of the world. Any problems you're likely to experience will come from critters: mice may munch on the sweet tubers below ground; deer and rabbits on the leaves above ground. One way to deter rabbits is to spray the plants with a solution made from three or four chopped garlic cloves soaked in two tablespoons (30 mL) of mineral oil, then combined with a pint (570 mL) of water and one tablespoon (15 mL) of fish emulsion. Dilute one part mixture with 10 parts water; refrigerate any unused portion. If deer are an issue, try hanging bars of strongly scented soap around the perimeter of your garden.