Brian Minter: Sweet potatoes have become a rising star

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In the past, we enjoyed them as a vegetable for Thanksgiving and Christmas dinners. Now, they are a year-round favourite, and many restaurants and fast-food outlets are offering sweet potato as a regular menu item.

In Ontario’s large vegetable industry, sweet potatoes are the rising star as folks are looking for healthier food alternatives. That province’s long, very hot growing season is ideal for sweet potato production, just as it is for watermelon, cantaloupe and honeydew melons.

Closely related to morning glories, edible sweet potatoes are actually the thickened root of the tropical, fast-growing ipomoea vine. There are many different varieties and colours of sweet potatoes, and each one has its own unique characteristics. As a rule, all of them are high in fibre and vitamins, and many have antioxidant, anti-inflammatory and anti-diabetic properties. Sweet potatoes also help boost our immune systems.

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On the west coast, for years now, we have enjoyed sweet potato vines as ornamental accents in our hanging baskets and containers. They outperform almost any other vine in hot weather. In fall, when we pull out these vines to replace them with cool season colour, we often find assorted sizes of sweet potatoes among the roots. Once properly cured, they are edible, but are somewhat bitter tasting and lack the flavour of regular edible varieties. One of the original ornamental ipomoeas, the hot lime coloured Marguerite, is a prolific producer of bright pink sweet potatoes.

About 15 years ago, I was contacted by Ken Allen who lives in Ontario. He had collected a series of edible sweet potatoes to test for growing in home gardens in Eastern Canada, and he had also authored a book about them, titled Sweet Potatoes for the Home Garden. One of his top varieties was Georgia Jet, and he thought folks on the west coast should give them a try. Of all the varieties we’ve tried, it has been one of the most productive and reliable.

Sweet potatoes are usually purchased as rooted or unrooted vine cuttings or slips from a few local growers or from online sources. Once a cutting is rooted in a pot, it’s simple to start more and to keep the plant growing as a source for even more plants. The cuttings root easily, often in a week or less, just by placing them in four-inch pots of quality potting soil, watering them in and covering them with lightweight, clear plastic. The cuttings will need misting a few times a day to keep the leaves turgid until they root.

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Edible sweet potatoes need a long, hot season for the best results. Once rooted, keep them in a warm spot where they will grow quickly. It’s important to harden them off outside in a protected area before planting them in the garden once nighttime temperatures in June are consistently above 10C. They need daytime temperatures of at least 70F (21C) to really begin their growth cycle, and they will tolerate temperatures of 104F (40C) or higher. For extra warmth and better production, use raised beds and cover the soil of the growing area with clear or black plastic to really heat up those growing roots.

A June start should result in a late September or early October harvest. Sweet potatoes require only minimal care: quality, well-draining soil, adequate watering and moderate fertilization. To feed, I would use a 10-15-19 formulation with micronutrients.

When harvesting, a fork is the preferred tool, and you need to be careful not to spear the tubers. Handle them as gently as eggs to avoid any bruising that could cause rot. Once harvested, the tubers need to be cured for about a week at temperatures between 85-90F (30-33C). By doing so, the sweet potatoes will form a second skin, which will hold in moisture and help the tubers last longer at room temperatures. This process will significantly improve the flavour and sweetness of the tubers. Don’t put sweet potatoes in the fridge or cold storage.

There are many new varieties worth a try here on the west coast. As I mentioned earlier, Georgia Jet is the old reliable one, but other tried-and-true performers are: Toka Toka Gold, Owairaka Red, Kamura, Korean Purple and B-18.

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Vineland, one of Canada’s leading agricultural research and innovation centres in Ontario, is doing extensive trials for growers and has introduced a new variety, called Radiance. It appears to be an outstanding choice.

There are also new crossover varieties that have both beautifully coloured foliage and quality tubers. Branded as Treasure Island ornamental sweet potatoes, these new home garden varieties come with attractive lime, purple or green lacy foliage and their tubers have white, orange or purple flesh.  These varieties have won many awards in Europe and will be more widely available in the U.S. and Canada this year. They are ideal for both container growing and warm garden beds. The five varieties in the Treasure Island series are all named after French Polynesian islands: Kaukura, Makatea, Manihi, Tatakoto and Tahiti.

Ornamental sweet potatoes have already made a huge impact in our summer baskets and containers. So, garden foodies, it’s your turn to discover and grow these many new, delicious and nutritious edible varieties.