Sweet potatoes

Sweet potatoes are densely packed with nutrients, delicious roasted or mashed with a dab of butter, and notoriously too heat-loving to grow in Canada. It can be done, though, and if you allow for a few simple requirements, they will be one of the most low-care vegetables in your annual rotation. Give it a try this summer and let us know how you did.

The toughest thing to get in Canada is warm soil for the entire growing season. You can get a jump on warming the soil by laying down some plastic in your planting area in May, once you can dig. Use black plastic sheeting. Till the soil first, then make mounds about 4 inches high and 18 inches apart. Cover the whole area with black plastic sheeting, weighted down at the edges with soil or stones. Do this a couple of weeks before you plan to plant your sweet potatoes.

Another tough thing is to get slips for planting. You don’t plant sweet potatoes by seed—the growing season is just too short. Rather you use cuttings of vine. You can start your own (see sidebar) or you can purchase slips. Perhaps your local nursery or your favourite seed catalogue sells them. (Winnipeg Sweet Potato is working to increase availability in Manitoba and Veseys sells slips online, for two consistent Canadian sources.)

Once you have soil warmth and slips, just plant them, water them and wait. If you have prewarmed your soil with plastic sheeting, cut a six-inch hole and plant through that. After planting, water the open spots of the sheeting well; you want the sweet potatoes to grow deep roots.

They don’t like very rich soil, so you don’t need to feed them much; some compost tea every few weeks will suffice. They do, however, like very loose soil like a sandy loam, something that would keep carrots happy. Keep them well watered until the end of the season is coming, then stop watering them about three weeks before you plan to dig up the harvest.

When should you harvest? As late as possible, knowing that sweet potato roots cannot tolerate cold. Storage below 13 degrees Celsius (55 degrees Fahrenheit) leads to chilling injury. Another reason to forestall harvesting as long as possible is that the end of the season is when sweet potatoes are putting the most growth into the tubers. The first eight weeks in the ground is when root lengthens, and it is the remainder of the growing season that the roots fatten up.

Be careful when you dig the sweet potatoes up because they have very delicate skin. When you have them out of the ground, put them in a warm place for 10 days, spaced out, to cure. A warm place means 25 to 30 Celsius (77 to 85 Fahrenheit). Then wrap them individually in newspaper and store them in a cool place at about 13 Celsius (55 Fahrenheit). Treated just right they will store for up to a year.

Listen to Podcast about Sweet Potatoes