Learn to grow a sweet potato

You don't usually equate the sweet potato with terms of endearment, but singer-songwriter James Taylor does just that when he refers to his girlfriend—who's responsible for the divine happiness he feels one particular day—as Sweet Potato Pie in his appropriately titled song “Sweet Potato Pie.” I fully understand: sweet potatoes (Ipomoea batatas) are sublime, not only with respect to taste and cooking versatility, but in nutritional value as well. These healthful superstars are an excellent source of vitamin A (in the form of beta carotene, which also offers antioxidant properties) and a good source of vitamin C, not to mention the dietary fibre and vitamin B6 they provide. And great news: if your region has at least a 100-day frost-free season, you can likely grow them, as an increasing number of Canadian gardeners have discovered. Short-season cultivars (90 to 100 days) such as ‘Georgia Jet' and Tainung 65 thrive in home gardens across the country, especially during dry, hot summers. (One gardener in Northampton, New Brunswick, raised a 3.4-kilogram Tainung 65 monster a couple of years ago.) But while they like it hot, sweet potatoes are no prima donnas. They require little watering, weeding or feeding, and they store well.

Planting and growing
Although members of the morning glory family (Convolvulaceae), sweet potatoes are not sown from seed, but rather from slips, small shoots that grow from the tuber that are then transplanted. While slips are not readily available at garden centres, there are a few Canadian suppliers you can order from—or you can grow your own (see “Let It Slip,” next page).

Sweets can't tolerate frost, so you should plant your slips about the same time you normally transplant warm-temperature veggies such as peppers and eggplants. Harden off as you would other tender plants.

Sweet potatoes prefer light, sandy, somewhat acidic soil (pH 5 to 6.5), but New Brunswick grower Greg Wingate of Mapple Farm notes they do just fine in his clay soil. Plant them in the warmest, sunniest spot possible. You can help speed soil warming (highly recommended, given the short summers throughout most of Canada) by planting in wide raised beds or rows about 20 centimetres high, and by covering the soil with sheets of clear or black plastic mulch several weeks before you plant; the soil needs to be at least 13°C.

On transplanting day, thoroughly weed the area. Wingate sometimes adds a side dressing of potassium-rich wood ash—which promotes stronger, more disease-resistant root growth (avoid excess nitrogen, which will produce lush, leafy growth at the expense of the tubers)—working it into the soil as he weeds. Cut holes in the plastic about 23 centimetres in diameter, and 45 to 60 centimetres apart; anchor the slips using soil, tucking them into the centres of the holes, leaving about two or three leaves above ground. Water well, and provide some shade for the first few days if there's a lot of sun.

Sweet potatoes can also be grown in containers, according to Ken Allan, a grower in Kingston, Ontario. At a minimum, you'll need a 30-centimetre pot—bushel baskets and half-barrels work well, too. The advantages are that the soil in containers will heat up quickly and you can move them to a warm, sheltered spot as needed. The main drawback is that the soil will cool faster than a bed in the ground, so be vigilant—a soil temperature of 10°C or lower will ruin your crop (below 10°C, harmful rot spots may form, turning your sweets into brown mush during storage). You'll also have to water more often, as the roots can't reach deep into the ground for moisture as they do in regular beds.