Growing Sweet Potatoes in Minnesota
Growing potatoes in Minnesota is easy, and you can grow many varieties, sizes, and colors. Sweet potatoes are a whole other story. They aren’t even in the same family as potatoes, who belong to the nightshade family. Sweet potatoes typically need a long, hot growing season – which can be a challenge in Minnesota. Read this article to learn the secrets to growing sweet potatoes in your back yard.
Michelle Scullard, Master Gardener
Growing potatoes in Minnesota is easy, and you can grow many varieties, sizes, and colors. Sweet potatoes are a whole other story. They aren’t even in the same family as potatoes, who belong to the nightshade family (Solanaceae), similar to peppers and tomatoes. Sweet potatoes belong to the (Convolvulaceae) family, as do morning glory flowers. Kind of makes sense when we recall the luscious sweet potato vines we often use in containers (purple and lime colored) and how much they do look like morning glory vines.
Unlike regular potatoes, sweet potatoes need a long and hot growing season. Sounds like a typical Minnesota summer, right? In many of our dreams, maybe. In Dakota County, we land firmly in USDA Growing Zone 4b, which means we have a little bit longer growing season than our fellow Minnesotans in northern Minnesota, but not as long as a sweet potato really needs. What this all means is that we have to put more work into successfully growing that yummy sweet potato.
It starts with choosing the right variety of sweet potato. The two most successfully grown varieties in Minnesota are “Beauregard” and “Georgia Jet”. Beauregard is considered to have great flavor while Georgia Jet is more consistently successful here. Both produce a harvest in about 90 days instead of the usual 100-170 days most other varieties require. You plant them after the danger of frost, which is around mid-May here, according to the MN DNR’s Last Spring Frost map (but keep an eye on those nightly temperatures).
Start the sweet potatoes from slips, not seeds. Sweet potatoes prefer a soil pH between 5.5 – 6.5. To provide as warm a planting site as possible, choose a location that receives at least 4-6 hours of sunlight per day. It is recommended that you mound the soil or create ridges that are 8-12 inches high, or plant in a raised bed. Place black plastic over the soil to help heat the soil and maintain the warmth throughout the growing season. It is suggested that you plant in the late afternoon when the soil has warmed. Plant the slips 10-18 inches apart in rows that are three feet apart, about 4 inches deep, making sure the roots are covered completely with soil. You want to leave space for the vines to spread.
There are differing opinions about whether to use fertilizer or not. Some people feel it detracts from the flavor, however, others think fertilizer is needed to produce a larger harvest. If you do choose to fertilize, it is recommended to use a balanced fertilizer, avoiding excessive Nitrogen. Place the fertilizer to the side of the plant (called side dressing) about six weeks after planting.
Water regularly, providing the plants with about ¾ of an inch a week initially, and watering more often as the plants mature. You will want to stop watering two weeks before you harvest. Carefully dig the sweet potatoes before the first frost (usually mid-October). Try to avoid bruising or cutting them by using a potato fork or even moving the soil away with your hands.
Once you harvest the sweet potatoes, you are going to have to wait between one to three weeks before eating because they need to ‘cure’. The curing process turns the starches in the sweet potato to sugars, producing the characteristic sweetness of the potato. If properly cured, you can store sweet potatoes at 55° F at high humidity for several months. Then, eat and enjoy!
References used in this article
Minnesota State Horticultural Society
Mother Earth News
Burpee (not an endorsement of any seed catalog as many garden catalogs carry sweet potato slips)
Photo credits: USDA. https://snaped.fns.usda.gov/seasonal-produce-guide/sweet-potatoes-yams (1), www/.scientificgardener.blogspot.com (2), University of Georgia Extension. https://extension.uga.edu/publications/detail.html?number=C1014 (3)