Growing Sweet Potatoes: Easy as Sweet Potato Pie!

Growing Sweet Potatoes is different from growing regular potatoes. Sweet potatoes are grown from “slips, ” the rooted sprouts from a sweet potato.

Family: Convolvulaceae

Botanical Name: Ipomoea batatas

Type: Herbaceous, perennial, annual       

Zone: 8-11 (USDA) (If growing outside.)

Soil pH: Acidic

Size: Between 2-20 ft. long

Growing Sweet Potatoes

Sweet potatoes are in the Convolvulaceae family whereas Irish potatoes are in the Nightshade family. And yams are in the Dioscoreaceae or Lily family. Sweet potatoes come in a variety of colors: white, yellow, orange, and purple. There are vine and bush varieties.

They are slow-growing plants that need warm temperatures to grow into full-sized tuberous roots. Plant them in the spring in your greenhouse for a late summer harvest. They will need three to four months of growing time and one plant can produce around 3 to 5 tubers.

  If you try to start a sweet potato by planting one in the ground it may rot if the soil is too moist. The best method of growing sweet potatoes is by growing “slips.”

Growing Sweet Potatoes: What are “slips?”

Slips are the shoots grown from a mature sweet potato. You can grow your own slips or order them online. Note: If you order them online they typically ship in May and June so they can be planted in warm soil. Starting slips yourself takes planning as they take many weeks to grow before you can plant them. Follow this link to learn more about growing sweet potato slips.

There are a few ways to make sweet potato slips. One method is the water method. Suspend your sweet potato in a jar filled with water by using toothpicks. Place the jar in a well-lit area, but avoid full sun if possible. This method can take 6–8 weeks.

The indoor soil method is quicker, taking about 4–6 weeks. For this method a heat mat is helpful and bright lighting is necessary. If the soil is kept too moist, the sweet potato may rot.

The outdoor soil method works well for those in warm climates but still takes 4-6 weeks.

Best Location in a Dome Greenhouse for Growing Sweet Potatoes

Sweet potatoes grow well in full sun and partial shade to protect them from the hot afternoon sun. They require warm soil temperatures and moisture. Remember they are typically a southern plant and don’t handle the cold at all. The central bed or eastern side of the Growing Dome will provide the ideal conditions.

Planting Your Sweet Potato Slips

Sweet potato slips are going to need loose soil to grow new tubers. This is one of the most important aspects of growing sweet potatoes. Plant the slip root down and cover half of the slip with soil. The top half of the slip with new leaves is above the soil. Plant the slips 12–18” apart.

Water the slips well, including all the surrounding soil once you have planted them. Water them daily for the first 7 days, then water every other day for the next 7 days. They will be fine with watering once per week after they are established. During a drought or very hot days, adjust your watering to keep them growing.

Sweet Potato Care

Sweet potatoes need to have regular watering for the first 50–60 days after planting. Once your plants are established they tolerate dry soil very well. It’s best to give them a deep watering between dry periods. Too much water can cause the roots to rot though.

For the last three to four weeks prior to harvest, don’t water your sweet potato plants. This will help prevent the tubers from splitting and prepare them for long-term storage.

Temperature is vital to growing sweet potatoes. The soil temperature should be between 60–80ºF with the air temperature between 65–95ºF. There are also short-season varieties available for those in northern climates.

A soil test is a great way to determine if your sweet potatoes will have the necessary nutrients. They are not heavy feeders like some other crops, but preparing the soil before planting them is wise. As with many other plants, soil that is too rich produces luscious foliage rather than the crop. Try adding compost or liquid fertilizer to the soil if needed prior to planting. In our May article about growing tomatoes, we mentioned singing or playing music for your plants. Well, guess what? Here’s a Sweet Potato Pie song with Ray Charles and James Taylor!

Growing Sweet Potatoes and Companion Plants

Companion plants are a bonus to any garden. Practicing companion planting will offer many benefits. First of all, they attract pollinators and beneficial insects. They help retain moisture and offer weed control. Lastly, they can add nutrition to the soil and thereby increase productivity.

Here is a list of the best companions for sweet potatoes:

Managing Pests

Growing sweet potatoes is easy, but that doesn’t mean there aren’t pests to be aware of! With sweet potatoes one of the biggest concerns is mice or voles (meadow mice). This is why we highly recommend using hardware cloth throughout the dome greenhouse. Wireworms can be a problem for root crops. They are common in most soils and are found year-round. They impact the growth and health of plant’s roots by feeding on them. Follow this link to learn more about wireworms and other crop pests and diseases.

Harvesting Sweet Potatoes

Sweet potatoes are ready to harvest between three and four months after planting. The foliage will start to yellow when they are ready. Be sure to dig gently when harvesting as their skin is tender. Simply brush the dirt off after harvesting them, do not wash the roots.

If growing outside, harvest your sweet potatoes before the first frost. If your sweet potatoes are still in the ground after the first frost do not let them stay in the ground long or they will rot.

Pruning Sweet Potato Plants

Sweet potato vines will wander through your garden so they need plenty of space. It’s important to allow them to grow without trimming them as they are an integral part of feeding your growing sweet potatoes. If they are getting out of control, simply hand-turn the vines in the direction you want them to grow. 

Sweet Potato History

So where did sweet potatoes come from? They are native to South America, specifically what is now known as Ecuador. Cultivated sweet potatoes were actually present in South and Central America 5,000 years ago. Sweet potatoes have also been found in Polynesia as well and carbon dated to 1210–1400 CE. It is believed that vine cuttings were brought from South America by voyaging Polynesians and then shared throughout the South Pacific.

Sweet potatoes are not related to potatoes either. Potatoes are in the Solanaceae or Nightshade family. Their relatives include tomatoes, peppers, and other nightshades. 

They are sometimes labeled as yams, but they are in different families. Sweet potatoes are members of the Convolvulaceae family, while yams are in the “I yam what I yam” family otherwise known as the Dioscoreaceae or Lily family.

Purple Sweet Potato History

The Okinawan purple sweet potatoes also have their origin in South America. In the 1400s Spanish explorers learned about them and then took them to China and the Philippines. Both the purple hue and the sweet flavor quickly garnered popularity in these countries.

In the early 1600s Noguni Sokan, a Japanese official trading with China, introduced Ryukyu, present-day Okinawa, to these purple sweet potatoes. They thrived in the climate of Okinawa and became a staple crop throughout Japan.

Due to storms that batter the island of Okinawa rice is difficult to grow. So while many Japanese eat “morning rice,” “lunchtime rice,” and “evening rice;” Beni imo, the purple sweet potato, grows well in the warm climate and has become a staple in Okinawa. 

Beni imo is difficult to find outside of Okinawa due to an infestation of potato weevils. These can cause significant damage to crops so it is prohibited to take them out of Okinawa unless they are steam-heated first. The steam-heat method is done at a low temperature of 47–48ºC, which keeps the sweet potatoes raw.

Sweet Potato Trivia

• Sweet potatoes are not potatoes. A sweet potato is a tuberous root and a potato is a tuber. 
• What about yams though? Sweet potatoes are in the Convolvulaceae family and yams are in the Lily family. The texture, taste, and skin are some of the other differences.
• Did you know that our first president was a sweet potato farmer before becoming president? He grew sweet potatoes on his farm in Virginia.
• A stainless steel knife is better when cutting a sweet potato than a carbon blade, which will cause the sweet potato to darken.
• For those who are diabetic, a boiled sweet potato has a low glycemic index so they won’t spike blood sugar as much as regular potatoes. Note: Baking, roasting, and frying are not healthy ways to prepare sweet potatoes for those with type 2 diabetes.
• How many grams of protein are in a sweet potato pi? 3.14159265
• Some varieties of sweet potatoes have a very low moisture content, such as the ‘Stokes’ variety. This variety is best roasted as attempting to cook it in a microwave oven will turn it into something like a charcoal briquette!

Health Benefits of Sweet Potato

Sweet potatoes are a superfood. They contain high levels of vitamin A, vitamin C, iron, and potassium. They have more nutrients than broccoli or spinach. What do you think of that, Popeye! Sweet potatoes are also a low carbohydrate food and high in fiber so you feel full longer plus you get all those amazing nutrients. AND they have almost no fat! Sweet!

Another great fact about sweet potatoes is that they have a high percentage of beta-carotene. Why is that important? Beta-carotene converts to Vitamin A, which helps reduce the risk of some cancers! Winner, winner, sweet potato dinner!

So if you love sweet potatoes, plant some in your dome! You can look forward to enjoying sweet potatoes in great recipes.

Tina Jones Marketing Assistant

I joined Growing Spaces in 2021 as a gardener and now work with the Marketing and Social Media department. Formerly I was a kindergarten teacher and then worked as a Gardener and Volunteer Coordinator at Maui Nui Botanical Gardens in Hawaii. Since moving to Colorado I worked in the veterinary field and have been involved in therapy dog work visiting hospitals, schools and libraries with a national therapy group. My previous dog and I also worked as a crisis response team helping those affected by crises or disasters and were deployed through Hope Animal-Assisted Crisis Response. Muppet and I are now a crisis response canine-handler team! Outside of working and volunteering, I love growing native plants and flowers at home, hiking, photography and hanging out with my husband and our dogs. I like to garden and volunteer with my therapy dogs in the community. My husband and I enjoying skiing and horseback riding. He helps build gardening beds so I can dig in the dirt and grow things.

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