In 2024, I was asked to write an article on growing sweet potatoes in Saskatchewan, which I did in the fall, as we tried several new techniques in the summer of 2024. I have included much of the information from that article, with the latest news for this season. We have been growing sweet potatoes in Saskatoon for about seven years, harvesting enough tubers that we can store them and eat some each week until the New Year. The harvest from last year has finally been eaten, and I have started plants from some of the small, sprouted tubers to provide slips for this season.
Sweet potatoes (Ipomea batatas) are native to tropical America and are related to the Morning Glory flowering plant. They are not closely related to our common potatoes (Solanum tuberosum) or yams (Dioscorea spp). Although the white fleshed sweet potatoes may be called yams in the grocery store, they are mislabelled. True yams are usually grown in Africa and Asia, not in North America.
Sweet potatoes require a longer frost-free period than is normally experienced in Saskatchewan, and extra care must be taken to give them warm soil and adequate water during the summer, and to protect them from frost in late spring or early fall. They are usually planted as shoots (slips) taken from parent plants, which have been placed in water for 5-6 days, until they have produced roots. We used to buy rooted slips from seed companies in Eastern Canada, but for the past few years, we have kept plants growing indoors through the winter, which can be used to produce slips in the spring. This spring, I have also started plants from the sprouted tubers to plant out in the bed in June.
Originally, we tried about 8 of the cultivars available, but for the past few years, we have grown only Covington and Japanese Yam (really a sweet potato). Covington has a brown skinned tuber with orange flesh, which I prefer to the red-skinned, white fleshed Japanese Yam. In 2024, we tried a new cultivar, Radiance, which is about 3 weeks earlier to mature than other available varieties. Radiance was bred in the Vineland Research and Innovation Centre, Ontario, and sufficient numbers of slips were produced in 2024 by an Alberta company for sale to Canadian growers. Radiance did very well in our garden, but unfortunately, the Alberta company did not have a good crop for producing slips in 2025. However, they are now growing a second new cultivar, Luminance, and have sufficient slips of this variety to supply in place of Radiance. Radiance produces orange-fleshed tubers, which I prefer, but I am willing to try the white-fleshed Luminance.
It is important to prepare a suitable growing environment for your slips. We dig our soil bed in mid-May, adding in compost, and then making a raised bed, the width of 1 row, like a hilled potato row, with a flat top and slanted sides. We run 2 soaker hoses on each side of the top of the row, cover it with a strip of plastic that is anchored with soil in the depressions each side of the row. You can use either clear or black plastic, as it is needed to warm up the soil. Black plastic has the advantage of reducing weed growth, but it is not difficult to loosen the plastic to remove weeds early in the season, and the dense growth of the sweet potatoes will crowd out the weeds by mid-season. We plant the slips in the centre of the row, through slits made in the plastic, at about 30cm apart (Photo 1). In 2024, the slips were encouraged to poke up through the slits, but the weather was dreadful, cold and windy for about 2 weeks, and the new plants were very slow to develop. Luckily, the season was long, with some hot spells, and eventually the plant tops grew vigorously as we could keep them well watered with the drip irrigation (Photo 2).
Harvest is exciting, as you don’t know what to expect. The green leaves and stems are cut off at ground level so the plastic can be rolled back, and the soil is dug away carefully. Most plants have a cluster of tubers hanging down near the main stem. Occasionally, the roots go searching for water, and then a tuber will be found away from the main plant. In 2024, our biggest tubers were produced on the Radiance plants. These tubers were 20-30 cm and weighed 600-700 grams each (Photo 3), but usually tubers range from about 300 grams to unusable thin roots, about 20- 30cm long. We keep a few plant tops attached to tubers initially, so we can identify the cultivar and save a few stems to grow on for winter plants.
Harvested tubers are placed in crates with good air circulation, but initially the crates are enclosed in large, plastic bags, for about three weeks at high room temperature, being careful not to allow high humidity and moisture build-up. The bags are then removed, and the cured tubers kept in the crates at room temperature for the remainder of the winter. We usually eat any damaged tubers and the smaller tubers first. Some of the smaller tubers can be kept till spring when they will often sprout and can be used to produce new slips.
Mice (or voles) like the tubers, and in our first year, several of the biggest Japanese Yam tubers were completely hollowed out. In 2024, the rodents again ate tubers, and interestingly, they again selected Japanese Yams and did not eat the orange-fleshed tubers. This may have been a chance selection, I have no data on mice preferences! We have only noticed insect pests once, about 6 years ago, when there were small green caterpillars (identified as caterpillars of the morning glory plum moth) eating new leaves. One spray of Bt insecticide was sufficient to reduce the caterpillar population significantly. We did not notice an impact on yield.
The book “Sweet Potatoes for the Home Garden” by Ken Allan gives excellent information on growing this crop and describes most of the older cultivars. There is also an article in The Gardener magazine that provides information on cultivation of sweet potatoes in the prairies (Summer 2017, Vol 23 Issue 2). Now we are growing Canadian varieties, and slips are being produced in Alberta; there will likely be more information online about growing sweet potatoes in Canada.
Jill Thomson is a plant disease specialist (retired) who enjoys gardening in Saskatoon with her family, including the dogs.
This column is provided courtesy of the Saskatchewan Perennial Society.
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