Sweet Potatoes

Adding sweet potatoes to your garden or landscape provides many years of heat tolerant foliage and delicious edibles. Sweet potatoes are referred to as a ‘long crop’ because they take 3 to 5 months to produce, but this durable perennial is a good investment of your garden space. Did you know that the leaves of sweet potato plants are edible? Read on!

Personally, I’ve always enjoyed a baked sweet potato with just a little butter and salt. They are so sweet all on their own, they really don’t need much else. Others prefer them sprinkled with brown sugar, or, in the Turkey Day favorite, covered with a layer of mini marshmallows. What I didn’t realize until recently, is just how easy sweet potatoes are to grow.

Sweet potato roots (Llez) CC BY-SA 3.0

Sweet potatoes v. yams

Before we get too in-depth, let's make sure we know the difference between sweet potatoes and yams. If you live in the U.S., you’ve probably never had a yam. Yams are from Africa and they can grow up to 6 feet in length and weigh in at as much as 150 pounds! Yams tend to be starchy and they need to be cooked before they are eaten, to get rid of toxins.

Sweet potatoes (Ipomoea batatas) are an entirely different critter. Sweet potatoes are from tropical South America, they tend to be sweet, and are significantly smaller than yams. The whole sweet potato/yam confusion began in the U.S. because sweet potatoes have two different growth varieties: firm and soft. Firm sweet potatoes were sold first, then the softer variety arrived. To differentiate them from their firmer brethren, soft sweet potatoes were called yams. Nutritionally, sweet potatoes far surpass yams. If you are going to invest space, water, and time: grow sweet potatoes. Here’s how.

How to grow sweet potatoes

Sweet potatoes love hot summers. These herbaceous perennial vines need only 30-39 inches of rainfall (or irrigation) a year and they prefer temperatures in the 75 to 95-degree F range. Sweet potatoes prefer loamy soil with a pH between 5.0 and 6.2. Like regular potatoes, sweet potatoes are easily grown in large containers, so soil pH adjustments are relatively easy. Simply add an acidifier to the soil mix at planting time. Sweet potatoes are started from transplants and vine cuttings. These cuttings are called ‘slips’.

​While it may be tempting to use grocery store sweet potatoes to start your crop, this is not a good idea. First, many growers treat store-bound produce with growth inhibitors. Plus, you have no way of knowing if your grocery store sweet potato is carrying pests or diseases that can compromise your soil for a very long time. It really isn’t worth the risk. Invest in sweet potato plants or bare root slips from reputable suppliers. The plants will last a long time and are worth the investment. Plants prefer full sun and should be installed in early spring. Plants should be placed in large containers or in hills that are one foot high and 3 feet apart. Cover the roots with soil but leave the stem above ground and water lightly. Mature plants only grow about a foot tall, but can spread 3 or 4 feet, so plan accordingly. Being highly frost sensitive, plants may need protection in winter.

Sweet potato pests & diseases

Like regular potatoes, sweet potatoes are susceptible to many fungal diseases, so be sure your plants never sit in water or soggy soil for long. Common diseases include crown gall, bacterial wilt, Alternaria, Anthracnose, Fusarium wilt, gray mold, rust, root knot, and root rot. Weevils, aphids, flea beetles, leafhoppers, and wireworms are the most frequent sweet potato pests.

Containerized purple sweet potatoes make a nice patio plant

Sweet potato trivia

Regular potatoes are underground stem tubers, while sweet potatoes and yams are actual root vegetables, like carrots and beets, in that they store reserve energy in root tubers. It doesn’t mean much in the kitchen or even in the garden, but botanists swear by these differences. In fact, if you have ever used beaters to whip up a batch of mashed sweet potatoes, you probably found a bunch of fibers wrapped around the beaters. Those fibers are vascular tissues! Also, like legumes, pineapple, mango, and sweet sorghum, sweet potatoes have evolved alongside a helpful bacteria (Gluconacetobacter diazotrophicus) that fixes atmospheric nitrogen, making it available to the plant.

Harvesting & curing sweet potatoes

Small sweet potatoes can be harvested and used at any time. Full-sized roots are harvested in fall. After carefully removing them from their hills (hopefully without causing them any damage), they should be placed in a warm, dry location for 8 to 10 days. This helps toughen the skin for better storage and heal any wounds. Stored properly, sweet potatoes can be held for several months.

​You can find a nice read about sweet potatoes where "botany meets the cutting board" at the Botanist in the Kitchen.