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How to Grow Sweet Potatoes: Start Your Own Sweet Slips

Sweet potato rooting

Rooted sweet potato with young slips almost ready to harvest.

Learning how to grow sweet potatoes is important. Not only are they an ancient food crop, a staple that has sustained and nourished mankind for thousands of years, but they are also highly nutritious. Sweet potatoes are the seventh most important food crop in the world.

Throughout the ages these sweet, orange, red, golden and sometimes white roots were valued so highly by early man, that they were often used as a form of currency and as a token of friendship between cultures. Today, this weirdly-shaped “potato” is making a comeback with gardeners — and for good reason.

Starting to Grow Sweet Potatoes

To begin at the beginning one must first make note of the fact that sweet potatoes are not Irish potatoes, nor are they yams. Irish potatoes are actually fleshy underground stems (aka tuberous stems) that belong to the nightshade (Solanaceae) family of plants. Other garden nightshades include tomatoes, peppers and eggplant. Yams are a type of tuberous perennial liana belonging to the Dioscoreaceae family. Yams are by far the most notable member of this family. The starchy tubers are the only edible portion of the plant. Raw yams contain measurable amounts of saponins, which can be slightly toxic when eaten in large amounts.

Sweet potatoes (Ipomoea batatus) belong to the Morning Glory (Convolvulaceae) family of plants. Within this family are many genera, of which Ipomoea is but one genus. The Ipomoea genus includes species such as moonflower (Ipomoea alba) and cardinal climber (Ipomoea multifida). Sweet potatoes and almost all common morning glories belong to the species batatus. In most gardens, this species is grown as an annual or tender perennial. All batatus have twining vines and large, showy trumpet-shaped flowers with distinctive heart-shaped leaves held aloft by long succulent stems. Sweet potatoes have large, fleshy, edible tuberous roots.

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With the popularity of ornamental varieties of sweet potato on the market today, there is some confusion as to which sweet potatoes are edible and which are not. Since some members of this family are poisonous, eat only the tuberous roots and leaves of garden-variety sweet potatoes, just to be safe.

And eat it you may, for true sweet potatoes are edible from top to bottom.

The leaves of sweet potatoes are relished as greens and pot herbs in many countries around the world, but particularly those with tropical to semi-tropical climates such as Central and South America, India and other parts of Asia. During my travels throughout Southeast Asia, the leaves of Ipomoea were a farmers’ market special. The raw leaves and tender petioles are sweet and crisp and are often served alongside spicy dishes such as curry.

In addition to being eaten raw, the leaves of sweet potato are also cooked. In Asia, we found them being lightly stir-fried or added as a last-minute green to broth-based soups. You can do the same with the sweet potato leaves from your own garden crop. Try them fresh in salads, pickled, stir fried or lightly steamed. Pick freshly opened, unblemished leaves and rinse in plain water. Wrap in damp paper towels until ready to eat.

Although the leaves are edible, sweet potato vines are grown primarily for their swollen underground roots. These tuberous roots act as storage vessels for nutrients and water, which the plant will use to survive adverse weather conditions such as drought. They are also used by the plant for reproduction purposes. Because the tuberous roots are used primarily to store dense amounts of nutrients for the growing plant, sweet potatoes are also a highly nutritious food for man and animal.

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Sweet Potato Nutrition

According to the Growing Sweet Potatoes Fact Sheet, published by the Maryland Cooperative Extension at the University of Maryland, a medium-sized sweet potato contains, “130 calories, 0 grams of fat, 17 mg sodium, 350 mg potassium (10%), 28 grams of total carbohydrate (10%), 3.4 grams of dietary fiber (14%), beta-carotene (about 16 mg), 26 micrograms folate (6.5%), 2 grams of protein, over 500% vitamin A (for both men and women), 47% of vitamin C, 4% calcium and 3.4% iron (based on a 2,000 calorie dietary requirement).”

So why should you know how to grow sweet potatoes? For one, they pack a nutritional punch, taste great and are low in fat, and will fill your belly every time. But they are also incredibly versatile and can easily be prepared using just about any method you can imagine. Whether you bake, boil, steam, fry, mash, dice or slice them, sweet potatoes have an uncanny flexibility that will suit even the pickiest eater and can be used to prepare everything from decadent baked goods to savory stews, soups and sauces.

Of course, sweet potatoes are a shoo-in for dishes like sweet potato pie or candied sweet potatoes, but don’t let their natural sweetness deter you from spicing things up a bit, too. One of my all-time favorite dishes made with these fleshy orange roots is sweet potato chicken curry made with lots of garlic, chili peppers and a plethora of Indian spices! The rich, savory-sweet stew is a real tummy warmer on a cold winter’s day and is a sure-fire remedy for anyone with a cold or the flu.

With a surge in popularity among gardeners and gourmet chefs, the homely root with the pumpkin-colored flesh is being grown in quantities not seen for decades. For those who already love sweet potatoes, that probably doesn’t come as a surprise. After all, sweet potatoes cover a lot of ground: They taste great, are easy to grow, relatively care-free and incredibly ornamental. But if you want to try growing your own sweet potatoes, you’ll need to hold back a few of those tuberous roots from the pot in order to start new sweet potato plants for the garden.

One of the drawbacks to growing sweet potatoes at home is that they need a long growing season to produce a good crop — anywhere from 90 to 150 days, depending on the variety. Sweet potatoes also require a lot of room for their delicate, but sprawling vines and will not tolerate cold, wet soil or frost at any stage of growth.

Sweet potatoes prefer full sun, but a bit of light afternoon shade helps retain moisture in the leaves and soil in areas with hot summers. Many a fact sheet on sweet potatoes will tell you that sweet potatoes need loose, well-drained soil, but I’ve been growing sweet potatoes in heavy Ozarks rock and clay for 12 years and have yet to be disappointed in their yield or form. As long as the soil drains well, you can grow a nice crop of sweet potatoes. If your soil doesn’t drain well or is overly rocky, work in plenty of compost, leaf mold, shredded leaves or straw in the spring and keep the bed well-mulched.

Sweet Potato Propagation

Learning how to grow sweet potatoes does not have to be hard. For the farmer and home gardener alike, sweet potatoes should always be propagated vegetatively through vine cuttings or root sprouts known as “slips.” The true seeds of sweet potatoes are viable, but don’t generally produce a reliable edible crop. True seeds are used primarily for breeding new varieties. Good quality, disease-free slips are available at many nurseries and seed houses, but you can easily start your own sweet slips right at home.

To sprout a sweet potato, begin with one or more slender, unblemished, organically- grown roots. Do not use the most gigantic root you can find. Instead, look for those that are 1-2 inches in diameter and 6-10 inches long. These young, slender roots produce more sprouts in less space and are less prone to rotting. Also, do not use sweet potatoes from the grocery store for sprouting unless they are labeled organic. Almost all commercially produced sweet potatoes are treated with an anti-sprouting agent that cannot be washed or worn off. You might be able to coax a few slips from one of these, but usually the tubers rot from the inside out before generating sprouts.

Avoid using sweet potatoes that have nicks, cuts, scars, bruises, sunken spots or any other kind of malformation as these can be indicators (and incubators) of disease. This is the reason you should never, ever plant chunks of sweet potato directly in the ground as you would Irish potatoes. It is also why you will never see sweet potato roots being sold for sprouting slips — sweet potatoes are prone to disease and the roots are the main carrier. Slips grown from potatoes are much less likely to carry and transmit diseases, which helps guarantee healthy crops from year to year.

There are essentially two methods for sprouting sweet potatoes — in water or in a hot bed. For most gardeners, sprouting in water is the most common method because it is convenient, cheap and effective. Plan to start the process about six to eight weeks before the last frost in your area.

The most common question asked about starting sweet potato slips in water is, “Which end goes up and which end goes down?” A quick search on the Internet will reveal the confusion surrounding this dilemma, but the answer is: Sweet potatoes will sprout from whichever end (or side) is up. Like most plants, sweet potatoes have an innate way of knowing where the sun is and will grow toward it like a magnet.

Find a large jar or other container into which you can easily fit the bottom third of a sweet potato. Any kind of vessel will do, but a quart-sized canning jar works exceptionally well. Start by filling the jar to the rim with water and inserting one end of the potato until about one-third of it is immersed in water — some of the water will be displaced. Remove the potato and insert three toothpicks evenly around the circumference of the root about ½-inch above the waterline mark you just made on the potato by dipping it in the water. Take care when inserting the toothpicks — push them into the root no more that ¼- to ½-inch deep.

Place the jar in a warm, sunny window. The warmer the spot, the faster the sweet potato will grow. If conditions are right, the sweet potato should begin sending out roots in 7-10 days and small sprouts and leaves should begin to appear within three to four weeks. Over time, the sprouts will elongate and grow stems — these will be your slips. Allow the sprouts to grow as long as possible before harvesting. Although I have planted tiny slips with success, ideally, they should be 6-8 inches long for best results.

Begin rooting the slips to set out in the garden approximately 10 to 14 days before the recommended outdoor planting date for sweet potatoes in your area. This information can be found online or at your local extension office.

The first thing to know when learning how to grow sweet potatoes is to remove the slip from the mother root and there are two ways to do this. Some sources recommend gently twisting the slips off at the bottom in such a way as to peel off a little piece of the mother root along with the slip. The idea is that the slip will root and grow faster with the bit of root than without it. Indeed, this is likely true and it has its benefits, but removing the bit of mother root also destroys the “eye” from which the slips grow. This not only creates an open wound in the mother root, but reduces the overall number of slips you could potentially get if left in place. Also, when you remove the eye with the slip, that bit of mother root might just be the carrier of a nasty disease, which will ultimately wind up in your garden soil.

When the slips are long enough, snip them off above the eye and place them in a jar of water to root, which usually only takes a week to 10 days. If your slips have suddenly turned into long vines, simply cut them into 6- to 8-inch lengths with at least one leaf on each, before placing in water to root.

I don’t have a lot of experience with the second method of propagation, which is a two-step process used primarily by large-scale producers. First the roots are pre-sprouted at a tightly controlled 75- 80°F at 90 percent humidity for about a month. As soon as the buds break, the roots are moved to sand-filled hotbeds where they are planted on their sides 2 inches deep and 1 inch apart. These are kept at a constant 75-80°F for an additional six weeks. This method, while not always feasible for the home gardener, is said to produce abundant and excellent quality slips.

Once all the slips have rooted and outdoor soil temperatures have reached 60- 65°F (usually about two to three weeks after the last frost date), plant the slips in the garden 2-3 feet deep and 12-18 inches apart. Keep well-watered until you see new leaves growing. You can actually plant un-rooted slips, too, but they must be kept moist and slightly shaded for up to 10 days before the roots begin to form.

A few more tips for growing sweet potatoes include planting them in well-drained soil with a soil pH of approximately 6.0 and using a three-year crop rotation to avoid diseases and soil pests such as wireworms and flea beetle larva. Finally, never plant sweet potatoes following a legume cover-crop as the excess nitrogen will enhance leaf and vine growth at the expense of root formation.

Sweet potatoes are a wonderfully delicious, nutritious and easy-to-grow crop. Sweet potatoes are heat and drought resistant, have few insect pests, and are at times just drop-dead-gorgeous.

Jill Henderson is an artist, author and organic gardener. She is currently the editor of Show Me Oz (showmeoz.wordpress.com), a weekly blog featuring articles on gardening, seed saving, nature ecology, wild edible and medicinal plants and culinary herbs. She has written three books:  The Healing Power of Kitchen Herbs, A Journey of Seasons: A Year in the Ozarks High Country, and The Garden Seed Saving Guide.

This article appears in the April 2014 issue of Acres U.S.A.

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