(Ipomoea batatas)

Sweet potatoes have been around for centuries. Domesticated sweet potatoes were present in Central and South America more than 5000 years ago. People obviously liked them and shared the bounty with others because now they are found all over the world including the continents of Africa, Asia, Europe, and Australia. The first Europeans to taste sweet potato were some of the members of Columbus’s expedition when they landed in Haiti in 1492. Now, most of the world can enjoy this sweet tasty versatile food in their kitchen, and garden.

We first discovered the joys of growing sweet potato plants a year after we got married. Marin had just returned to Arizona from New York missing the greenery and ivy that grew wild there. The hottest part of an Arizona summer was just beginning, and not a season of weather we generally look forward to.

That May we plunked a leftover piece of a purple sweet potato in the ground. We put it right under the eves of the house not far from where the A/C unit left a constant condensation drip. Most plants this time of year wilt no matter how much water you give them and seem as if they will turn to dust if you touch them. But for this sweet potato, in the miserable summer heat, oh joy of joys! It thrived and quickly became a lush groundcover reminiscent of the ivy Marin so fondly remembered in New York! It took off and filled that entire border area so well that we had to trim it back drastically every time we mowed the lawn!

We have learned much about growing and using sweet potatoes since then and now we highly recommend this incredible plant for anyone who is growing an edible landscape! Not only are the tubers tasty and colorful and the greenery beautiful, but it is a two-for-one crop. Sweet potato leaves taste great too!

SWEET POTATO OR YAM?

This topic usually needs some clarification. The many different types of “Sweet potatoes” and “yams” found in markets in the continental United States are generally the same species, Ipomoea batatas. “Batatas” is the name that the native people in Haiti called them when Columbus arrived. The Spanish later changed the name to Patatas, and then when introduced to the common potato, they also called that patatas. Now we call them sweet potatoes because they resemble a potato, but the Ipomoea was there first!

Here’s where the names “sweet potato” and “yam” gets confusing. The tubers that we eat may be classified by their two different characteristics of texture when cooked. These two distinctions are those that become moist-and-sweet when cooked, and those that remain somewhat dry and flaky (resulting in different ideal uses in the kitchen). Some varieties are able to convert more starch to sugar during cooking and will be more moist and sweet. These are often marketed as “yams” while the varieties that are comparatively drier and starchier are usually differentiated as “sweet potatoes”. Unfortunately, that doesn’t always apply and they may be marketed with interchangeable classification. Generally, the drier ones are not as readily available to home gardeners and are less common in markets due to less popularity, giving rise to markets using the appellations “yams” and “sweet potatoes” more fluidly.

To complicate matters, “true yams” of the genus Dioscorea are often sold in international markets in bins right next to bins full of Ipomoea sweet potatoes and yams. Sometimes they go by the name “yams” and other times they go by “ñame”, the common name of yams in many Latin American countries. Another species of Dioscorea is called “yamaimo”, or “Chinese yam”, one of the varieties of Dioscorea from China or Japan. Occasionally there are other Dioscorea species available as well, but as true yams are a very interesting topic, we will save that discussion for another post. True yams are generally not as sweet as Ipomoea cultivars, which is why the differentiation “yam” can be so very frustrating. Note: while the leaves of sweet potatoes are edible and delicious (as will be discussed later), the leaves of most Dioscorea species are toxic, and even fewer of the tubers are safe to eat raw.

CHOOSE IT:

RELATIVES

In addition to the sweet potatoes that we are familiar with, the genus Ipomoea also contains several perennial wild types and relatives globally. Upon inspection, you will see that they all bear the signature flower of the common garden morning glory and moonflower, which are members of the genus though generally not considered edible without extensive preparation. In North America, there are a few that can get quite large (known colloquially as “manroot”) and are supposedly best when the roots are carrot size. One such is Ipomoea pandurata known by some indigenous American peoples as “mecha-meck”, and another is I. leptophylla. I. aquatica, also known as “kang kong” or “water spinach”, is invasive, and in some places illegal, aquatic species grown in Asian communities for its delicious greens. There are many other edible and medicinal species of Ipomoea around the world including I. mauritiana, I. costata, I. simplex, and others. Identification and methods for processing Ipomoea vary according to species and we will not go into detail here.

Ipomoea batatas, our common tetraploid sweet potato, only exists as we know it in cultivation. While not particularly cold hardy, in theory, it could potentially be crossed with some of its cold-tolerant wild relatives such as I. pandurata. Worldwide there are somewhere between 6500-7000 different varieties of the familiar domesticated sweet potatoes, with new ones coming out all the time. In the United States, there are roughly 100 popular ones. Here are some of the more common sweet potatoes that we have grown.

NOTABLE CULTIVARS:

‘All Purple’ (120 Days to harvest); Dark purple flesh with purple skin. Hardier than most. A fast and strong Grower (deep and long brittle roots may need containing). Roots are dry and starchy, slightly sweet, and store well. Best tubers are grown from slips. Will become fibrous and inedible if left in the ground too long.

‘Beauregard’ (90 days to harvest); Orange flesh with red-orange skin. Vigorous vines. The early-maturing variety produces high yields.

‘Centennial’ (100 days to harvest); Orange flesh with copper skin. Fine-grained. Early. Semi-bush vines produce tapered roots. A commercial standard in U.S. High yields and a good keeper. Performs well in clay soils.

‘Georgia Jet’ (90 days to harvest); Deep orange flesh with red skin. Moist. Very fast-growing semi-bush type.Early producer.

‘Ginseng’ (120 Days to harvest); Orange flesh with pale orange skin. Vigorous semi-bush vines. Prolific producer. Dry, but sweet. Distinctively lobed “trident” shaped leaves.

‘Hernandez’ (120 days to harvest); Orange flesh with light red skin. Reddish-purple-stemmed. High yields from vigorous vines may produce some “football-sized” tubers in each bunch. Mid-season. Very sweet and moist when cooked. Great baking potato.

‘Jewel’ (100 days to harvest); Orange flesh with copper skin. Moist. Vigorous semi-bush vines produce uniform roots that are good keepers. Mid-season.

‘Red Japanese’ (95 days); White flesh, with red skin. Dry but sweet. Popular in Asian markets. Vines of average vigor are disease resistant. Heavy producer (if watered well). Midseason. Cultivars we want to try:

‘Okinawa Purple’ Deep purple flesh with light beige skin. Slow vines. Very late.

‘Okinawan’ Purple flesh with pale purple skin. Slow vines. Very late.

‘O’Henry’ (100 days); White flesh with white skin. Sweet and creamy. Short busy vines. Early producer. Heirloom.

‘Porto Rico Bush’ (110 days); Copper skin covers sweet, moist, Deep orange flesh with copper skin. Moist. Compact bushy vines.

‘Vardaman’ (110 days); Deep red-orange flesh with yellow skin. Bush variety with burgundy-bronze new foliage. Midseason.

‘White Hayman’ (100 Days); White flesh with cream skin. The flesh is starchy and sweet and turns more yellow when cooked. A good substitute for “Irish Potatoes,” but with a sweeter flavor. Vigorous vines produce large uniform roots. Midseason. Heirloom.

Sweet potatoes come in many different foliage colors and textures. All ornamental varieties that can be purchased from your local garden center will have edible and nutritious leaves, which is why they are perfect for an edible landscape! (though very few will produce a tuber and even fewer that do will prove palatable). We often see the purple leaves next to the chartreuse green leaves that make a perfect pop. All are edible, but some are sold for their glamorous foliage, others for their tasty roots, and still others are cultivated specifically for their tender, flavorful greens.

PLANT IT:

SOIL PREPARATION

One of the most important things to consider when planting sweet potatoes is that they require a loose and “roomy” soil 8-12” deep to grow good tubers. Fail to provide this, and other aspects of planting and soil preparation will matter little, as your tubers will be no bigger, and of no more culinary value, than a doorstop.

PROPAGATION METHODS

The most common method of propagation is by “slips”. Slips are vegetative shoots that come from the tuber itself. These can be obtained by rooting a tuber, or a piece of the tuber, in a jar of water using toothpicks to suspend it partially submerged in the water. Keep the water fresh. The new shoots that result within a few weeks in a sunny windowsill or under a grow light can then be removed, and themselves rooted in water. Good slips will have sturdy, thick stems, be 6 to 9 inches long, and have at least 5 leaves. One medium-sized sweet potato should yield about 12-20 good slips.

Within a few days of placing slips in water, they will have inch long roots and will be ready to plant. These will have the highest likelihood of forming beautiful spuds. In areas with a long growing season, such as ours, you can also remove shoots from an actively growing plant and root them in water for transplant, though some sources say that the resulting tubers may be more fibrous- I have not noticed. Whichever method you choose, lay the sprigs sideways an inch or two under the surface 18” apart and top with compost and organic mulch.

I have also simply placed a sweet potato in a brown paper bag on the back porch in late April until it sprouted and then planted it. Tubers still result and it’s less effort!

PLANTING SEASON

The best time of year to plant sweet potatoes in our area is March to June, usually whenever you would also be planting okra. They both love that heat!

GROW IT:

MICROCLIMATES

Sweet potatoes are a tropical vegetable and appreciate the long, hot, humid summers. When it’s too hot for me and most of my garden, sweet potatoes thrive. The ideal location for growing thriving sweet potatoes is a position in the all-day open sun, though they can grow (with smaller tubers) in locations that receive a partial day’s shade. While sweet potatoes do not prefer reflected heat, most varieties can take it, as long as they have sufficient water.

COMPANION PLANTING

We have found in our own gardening experience that they make good companion plants for our banana trees, as they have the ability to shade the soil and improve fertility in the surrounding bed. They would also work well as a companion plant for ginger, canna lily, lemongrass, garlic chives and any other complimentary strap-like foliage that can hold up to the groundcover’s desire to “cover” its companions.

LANDSCAPE USES

Sweet potatoes make a marvelous summer ground cover to shield, protect, and nourish the soil. They look great covering a sloping mound, or greenery butting up against a lawn or a walk. Every container for effective curb appeal must have 3 features: a “thriller” in the center to catch the eye and provide a focal point, a “filler” to buffer the base and provide additional color, and a “spiller” to give the pot a skirt of foliage; a wall of greenery. In a sunny spot or hanging over a wall, sweet potatoes fill this function with stunning excellence. You may even be graced with some of the gorgeous morning-glory flowers late in the season.

As part of their effectiveness as a cover crop, they have also been found to have an allelopathic relationship against certain weed species. Of particular mention is their skill at making the soil environment less suitable for yellow nutsedge, an annoying perennial weed in warm weather climates that is very difficult to eradicate in cultivated and uncultivated areas alike.

CARE FOR IT:

WATERING

Because sweet potatoes are a water and nutrient storage organ for the plant, they form as the long days wane and require regular watering for sizeable tubers. The plant is, however, fairly drought tolerant and will survive periods with little moisture, though the tubers may be of poorer quality. Sweet potatoes will produce the best tubers if they are watered regularly, starting with daily dosages the first week after planting and slowly weaning back the quantity throughout the season, while still maintaining consistency. Make sure that the watering is deep during hot, dry periods for best tubers. However, if plants receive too much water late in the season many varieties will crack and attract pests such as earwigs and woodlice, which will cause further damage to your tuber crop. The resulting tubers look more like garden goblins than those smooth sweet potatoes that you buy in the store. The trick is to find that balance.

FEEDING

While fertilization during the active growing season is not generally necessary because of its nature as a biodynamic nutrient accumulator, it is essential to start with a soil that has good tilth and have some level of organics and phosphorous. For extra vigorous plants, you may consider an occasional application of compost tea or liquid organic fertilizer as a foliar feed after the plants have been in the ground for a month or so. Be conservative, as too much nitrogen will result in excessive growth that will be a prime target for pests such as flea beetles, aphids, caterpillars, and crickets. While this largely doesn’t affect your tubers, if you are also planning to make meals out of the leafy vegetable part, this may present a problem. In short, feeding is helpful, but not too much!

MAINTENANCE

Pruning should be moderate. If you find that the plant is escaping its bed and traversing areas you would rather it not, simply pick up the vines and throw them back into the bed. By evening the leaves will likely reorient and you may not even be able to tell what you did.

MULCHING

We have found that a 2-3” layer of wood chips works wonders as a surface mulch for this plant. The chips keep the moisture in and evenly distributed while simultaneously providing a slow feeding as they break down. It is valuable to have a buffer layer of compost under the wood-chips to ensure that the plants are not starved of nitrogen. The added bonus is that the tubers form near the top of the soil just under the chips. Simply reach down under the mulch and pull up a tater for lunch (although it won’t have been cured yet)! This is an ideal way to maintain the aesthetics of the groundcover in the landscape and still get a harvest. The other advantage of this is that it prevents the vines from rooting in as they go across the ground. Instead of getting a million tiny tubers, the energy is spent on the tubers you will be harvesting.

HARVEST IT:

WHEN TO HARVEST

Sweet potatoes take about three to four months to reach maturity. Know your variety- If you let them go too long they may start to get tough or invite pests, but they are usually ok to leave until the first light fall frost. You can begin harvesting them as soon as they are big enough for a meal. Usually, sweet potatoes are ready to harvest when the leaves and ends of the vines begin to yellow. Some of the late-season varieties are best harvested after the first frost has turned the leaves black. If you are harvesting late, dig them out and leave them to sit on the ground with the dirt on them for another couple of cold nights to improve the flavor. This practice will depend upon the variety.

HOW TO HARVEST

Start by cutting the vines back to a six-inch shrub. This allows you room to work and a landmark for your digging. Most varieties will be found 4-6 inches deep in the soil with some vigorous varieties (like the ‘All Purple’) found deeper. If the tubers were grown in a raised bed or hilled they may be easier to dig out. Use a spading fork or broadfork to avoid the common mistake of slicing through tubers with a shovel. Loosen the dirt in a wide berth around the crown of the plant providing room around the roots so you don’t damage your crop. You may want to carefully lift the plant and use your hands to dig up the tubers, as they bruise easily. After digging up the tubers, shake off any excess dirt, but do not wash the roots.

The leaves are best in the early and mid-season but may be picked all summer long until the frost gets them in the late fall. Do not harvest too much, however, or you will be doing so at the expense of good tubers.

PROCESSING/CURING

Sweet potatoes need to be cured to develop maximum sweetness. Essentially this thickens the skin and heals over scratches that occurred during harvest. To begin that process a neighbor friend of mine recommends leaving the sweet potatoes out on the porch for the night after harvesting in cool weather, dirt and all. She said that’s what made them the sweetest!

Initially, they should be kept in a warm place but not too hot- about 75-85°F, ideally with a humidity of about 80-90% for 1-3 weeks. Warmer than that and they will sprout; too moist and they will spoil; drier than that and the skin won’t toughen up enough. Do not wash them however, as any residual moisture on the roots can cause them to spoil faster. Maintain good air circulation to prevent spoilage during curing. Placed in paper bags on the back porch in the shade with a wet towel on them works, placed one layer in a plastic grocery bag with holes on a sunny windowsill works, or in a storage tub on a rack with some water in the bottom works. Whatever your method, you have options. In the warm south where fall is still very warm (like here in Arizona) a garage or a shady garden shed works well for the location to cure them.

If you live in a more humid part of the United States an outdoor location in the shade works because the latter part of the summer usually includes humid weather. Some people pack them in crates of clean damp sand, but it is better if they have air circulation and are not touching. For this reason, you may opt to leave them in a single layer and use a small fan to improve the air circulation to prevent spoilage.

STORING

After curing, sort sweet potatoes and discard those that are bruised, sprouting or molding. You can then place them in the sand or wrap the tubers in a breathable newspaper and pack them in a box or basket for long term storage in a root cellar, basement, pantry, or garage. The ideal location for long-term storage would maintain a temperature range of 55°-60°F and 60% humidity for a minimum of 6 weeks. Storing in this way will improve the keeping quality and flavor yet more. If the storage location falls below 55 degrees for too long the centers of the potatoes may develop hard, white spots, but If it remains too warm, 60 degrees or higher, the potatoes may soften and shrivel and start to sprout. Stored properly, the tubers should last for up to 6 months.

Some people recommend putting an apple in each box of sweet potato tubers to prevent them from sprouting. This is probably because an apple releases ethylene gas as it continues to age. The gas acts as a growth suppression and fruiting hormone. Personally, I think that I would rather not find a rotten apple in my sweet potatoes a few months down the road, especially since The ripening enzymes found in the sweet potatoes themselves can accelerate the ripening process of other fruits and vegetables.

Without going through the effort for long-term storage you can keep sweet potatoes in a cool room for a few weeks in root form and a little longer in the fridge. For long-term cold storage (up to a year) they really should be diced or sliced, then cooked, or cooked then mashed before vacuum sealing and freezing. Adding some lemon juice to them will help maintain the vibrant color. We have found that slicing, roasting and freezing them works great for long term storage and convenient for later use.

The leaves work well frozen if you plan to use them within six months. For safety reasons we recommend blanching the leaves and then straining quickly and dropping them in ice water, then pat dry prior to freezing or dehydrating them. For leaves taken from our own yard we usually just rinse them and throw them in a freezer bag or use them directly.

USE IT:

TUBER VERSATILITY

Sweet potatoes can be used in curries, chutneys, casseroles, desserts, roasted, sauteed, boiled, baked, or cooked in a crockpot with other vegetables. They often make a superior substitute to pumpkin in dishes as well. Their uses are nearly endless. The drier, starchier varieties are sometimes used as a potato substitute, while the moist varieties don’t make good potato substitutes, but rather lend their own unique virtues to the culinary experience.

One of the best traditional uses is of course baked. The tubers should be washed clean, poked with a fork several times, then coated in olive oil and placed on a cookie sheet. Bake at 400°F for 40-60 minutes. Do not wrap in foil so that the sugars can caramelize. When they are done they will be soft when you squeeze them. Watch out it’s hot! Or you can cook them in the microwave on high for 4-6 minutes. They will be soft once cooled.

EAT YOUR GREENS!

Aside from the sweetest and tender root that is so familiar on our Thanksgiving plate, the leaves have a variety of uses in the kitchen as well. The leaves are great for stir fries, green smoothies, salads, and casseroles.  One amazing quality is that the leaves hold flavor better than any green I have come across. If you season them well and saute in the flavor, they can be put into any dish such as quinoa or rice as a savory spinach substitute. One of our favorite recipes using the leaves is Savory Garlic Chicken Bake on a thick bed of sweet potato greens. While they do not disintegrate when cooking like spinach does, they cook down a lot and it is easy to use a whole bag full in one dish.

FEEL IT:

THE TUBERS

These naturally fat-free vegetables are rich in protein, fiber, sugars, and carbohydrates, but are lower in calories, and have a lower glycemic load than traditional Irish potatoes. The vegetable as a whole has a strong anti-inflammatory effect, whereas yams and Irish potatoes are moderately inflammatory.

An average sized cooked tuber without salt contains 37% of the recommended daily value of Vitamin C, along with Vitamin K, and B Vitamins Thiamine (B1), Riboflavin (B2), Niacin (B3), Pyridoxine (B6), and Folate (B9). This dish also provides 438% of the recommended daily value of Vitamin A, which comes in the form of carotene. Carotene, once quickly converted into Vitamin A, has powerful free-radical fighting properties. Additionally, it is rich in other antioxidants, anthocyanins, chlorogenic acid, coumarins, and other nutrients.

Let’s not forget the minerals! It contains approximately 28% of the recommended daily value of Manganese, as well as high concentrations of absorbable Calcium, Iron, Potassium, Phosphorous, Magnesium, and Copper.

THE LEAVES

We love our summer greens! Part of our beloved morning routine includes going out in the morning to forage greens from our landscape, including sweet potato leaves, for our morning green smoothie. This tradition is largely to take daily advantage of the nutritional supplement provided by the greens that we are using.

Sweet potato leaves have many of the same nutrients as the tubers and are a great source of vegetable protein, Calcium, and Iron, and are highly anti-inflammatory. They are a very good source of Vitamin A, Vitamin C, Vitamin E, Vitamin K, and B Vitamins Thiamine (B1), Riboflavin (B2), Niacin (B3), Pyridoxine (B6), and Folate (B9). As a green leafy vegetable, they are also high in Magnesium, Phosphorus, Potassium, and Manganese. Vitamins A, E, D, and K are fat-soluble minerals essential for building strong bones, cartilage, teeth, and hair.

Sweet potato leaves contain a small amount of oxalic acid, which adds to the pleasant flavor, but not enough to harm and therefore may be used raw as well as cooked. The leaves are also a great source of dietary fiber and very beneficial for maintaining the digestive tract, as evidenced by the slightly mucilaginous texture. There is also strong evidence that many nutrients in the leaves are anti-mutagenic, therefore showing potential as a wholesome anti-cancer food.

FINAL THOUGHTS

The sweet potato plant is one of the best options for a great edible landscape, not to mention one of the easiest groundcovers to grow!  We hope this information leads you to a bounteous harvest in your progress to paradise!

How are your sweet potatoes growing? Any ideas, suggestions, or recipes that have worked for you?  Please comment to share!

Happy growing!