Common Name: Sweet Potato, Creeping Yam, Kūmara
Scientific Name: Ipomoea batatas
Family: Convolvulaceae (the Bindweed or Morning Glory family)
Sweet Potatoes are perennial in climates warmer than USDA Zone 8 or 9, and are grown as annuals if the climate is cooler; however, I personally think that with some experimentation and large trials, we could push perennial growth into colder zones. However they are grown, Sweet Potatoes are a wonderfully nutritious plant. The majority of people are familiar with the sweet, orange flesh of the tuber, which may also be white, yellow, purple, violet, pink, and red! But most Westerners do not know that Sweet Potato shoots and young leaves are edible and are considered a tasty vegetable in many parts of the world. In addition, Sweet Potato makes a great animal fodder – all parts are edible, and the fast-growing, beautiful vines make an effective groundcover, especially in perennial locations. Sweet Potatoes should be incorporated into most Permaculture designs!
Sweet Potatoes were likely domesticated in Peru by 8,000 BC, and they either had a second domestication or were transported to Central America and grown domestically by 5,000 BC. Although there appears to be growing evidence that the origin of our modern Sweet potato was on the Caribbean coast somewhere between the Yucatan Peninsula in Mexico and the Orinoco Delta in Venezuela. There is also strong evidence that supports the Polynesian explorers visiting South America and bringing back Sweet Potatoes around 700 AD. In modern times, Sweet Potatoes are grown around the world in tropical and subtropical climates for human food (tuber and leaves) and as animal feed.
- Sweet Potatoes are NOT yams, although in the U.S., Sweet Potatoes are often called “yams”.
- Yams are tuber plants in the Dioscorea genus originating from Africa, and are typically drier and starchy.
- Sweet Potatoes are tuber plants in the Ipomoea genus originating from South America.
- Sweet Potatoes are considered “root tubers” which means they have modified roots called “storage roots”.
- Regular potatoes are considered “stem tubers” which means they have modified stolons (stems) that enlarge just below ground.
- Sweet Potatoes can have beige, brown, yellow, orange, red, or purple skins.
- Sweet Potatoes most commonly have light or deep orange flesh, but white, yellow, purple-blue, violet, pink, and red-fleshed varieties exist.
- Not all Sweet Potatoes produce tubers that are edible… they aren’t poisonous, but they do not taste good.
- Sweet Potato leaves and shoots are a common vegetable in many parts of the world, and some varieties are grown only for the leaves.
- Not all Sweet Potatoes produce leaves or shoots that are edible… they aren’t poisonous, but they do not taste good.
- While Sweet Potatoes do best in hot and humid climates (Zone 8 and warmer), they can still be grown for tubers if the Summers are hot enough for long enough. If the climate is too cold for good tuber production, they can easily be grown for leaves/shoots as an annual vegetable in almost any location.
- Tubers can take 2-9 months to mature, depending on the variety.
- The Sweet Potato is considered the 7th most important food crop in the world.
- The Sweet Potato is the state vegetable of North Carolina (United States), and this state is the lead producer of Sweet Potato in the US.
- China is the world’s largest producer of Sweet Potato at 105 million tons (95,250,000,000 kg)! Half of it is used for animal feed.
- People from Papua New Guinea consume about 1,100 lbs (500 kg) per person per year!
- Americans consume about 4.5 lbs (2 kg) per person per year.
- Random Bit… every time I read about Sweet Potatoes and see the genus (Ipomoea), I hear the tune for “The Girl from Ipanema” in my head!
USING THIS PLANT
- Edible Tubers – the root (tuber) of Sweet Potatoes almost need to description. The large tuber is sweet, moist, and fleshy, but there are some varieties that are considerably less sweet and/or less moist. The tubers are usually cooked – baked, fried, steamed, roasted, etc. The cooked potatoes can also be thinly sliced and dried. The dried potatoes can be used in soups or stews or can even be ground into a flour.
- Edible Shoots/Leaves – the top 3-4 inches (7.5-10 cm) of growing (shoot) tips are used as a vegetable, as are the small, young leaves. Cooked – treated like most other “greens”.
- Ornamental Plant – Sweet Potatoes are commonly used as an ornamental plant. The vigorous vine has attractive foliage and can come in a range of colors and shapes.
- Groundcover Plant – very effective due to its fast growth.
- Drought-Tolerant Plant – Sweet Potatoes can be fairly drought tolerant once established (after about 80-90 days… after the tuber initiation stage) as perennials.
- Animal Fodder Plant – the tubers, stems, and leaves can all be used for animal feed.
- Sweet Potatoes can be used to make alcoholic beverages (wine and liquors).
- Industrial uses for starch and alcohol (ethanol) – research is being conducted for biofuel.
Yield: Variable. It all depends on how it is grown, where it is grown, and the variety.
Harvesting: The shoots can be harvested at anytime. The tubers can be harvested at anytime as well, if the plant is a perennial. If the plant is treated as an annual, than they are harvested at the end of the growing season (before the first frost).
Storage: The tubers can be used fresh or stored, but they need to be cured first. The simplest way is to let the tuber (unwashed!) sit in the sun for about a week or so when the temperatures are over 77 F (25 C) and the humidity is high. The cured tubers will last for many months (often up to a year) if kept in a cool, but not cold, location and handled as little as possible. Ideal storage is around 60 F (15 C), and there is conflicting information on whether dry or moist storage is best.
Using Stored Potatoes: Sweet Potatoes that are cracked or have large wounds (sustained from harvesting) that have not sealed during the curing process should be eaten first. Any Sweet Potato that is showing bruising should be eaten next. Sweet Potatoes with wounds that did seal during the curing process should be eaten next. Finally, the non-cracked, non-wounded, non-bruised tubers, which are the ones that typically store the longest, should be eaten last. Stored tubers can also be planted the following year.
DESIGNING WITH THIS PLANT
AHS Heat Zone: 12-1
Chill Requirement: Unlikely, but no reliable information is available.
Plant Type: Herbaceous Vining Plant (non-climbing)
Leaf Type: Deciduous
Forest Garden Use: Underground Layer, Vining Layer, Groundcover Layer
Cultivars/Varieties: There are a number of varieties available.
Pollination: Self-sterile (the vast majority of Sweet Potatoes are grown from slips, cuttings, tubers, or tissue culture). Sweet Potatoes need cross-pollination from another variety in order to set seed.
Flowering: Summer. Flowering events are rare for Sweet Potatoes grown in Temperate Climates. Flowering typically occurs in the Tropics or Sub-Tropoics, and is triggered by changing day length.
- Years of Useful Life: No good information available as we typically harvest the tubers and eat them. Considering that the plants can be propagated so easily, an individual’s life span is likely irrelevant. But I would like to know this for those living in warmer locations and using Sweet Potatoes for groundcovers.
PHYSICAL CHARACTERISTICS OF THIS PLANT
Roots: Large to very large tuber with small fibrous roots
Growth Rate: Fast
GROWING CONDITIONS FOR THIS PLANT
Shade: Tolerates light shade (Sweet Potatoes tolerate more shade in hotter climates)
Moisture: Prefers moist soils.
pH: 5.5-6.5 (prefers slightly acidic to neutral soils, but can still produce in less than ideal conditions; however, there are reports that state diseases occur more as the pH becomes more neutral.)
Special Considerations for Growing:
- Sweet Potatoes love the heat, and they really like humidity. But they really don’t like wild changes in temperatures, so it is important for them to planted once the temperatures stabilize. After that, the more heat, the better… within reason!
- Sweet Potatoes do not like to be transplanted, so either plant in place or transplant as few times as possible.
- Be sure to plant potatoes that are disease resistant and virus free if possible.
- Planting in raised mounds or raised rows/beds makes for easier harvesting.
- “Hilling” can be done (mounding up the soil or adding compost or mulch around the base of the plants) helps tuber development and prevents dehydration of the tubers.
- If growing as an annual, rotate the Sweet Potatoes’ location to minimize nematode problems.
- Sweet Potato can be propagated from seed. Like most species in the Morning Glory family, scarifying the seed or soaking the seed for 12-24 hrs before planting will increase germination. Sweet Potato seed may not yield plants with the same quality as the parent (i.e. they are not “true to type”).
- Sweet Potatoes are often propagated via stem cuttings; these cuttings come from the terminal tips of a growing shoot, should be 7.5-18 inches (20-45 cm) long, and should contain at least three nodes. The lower leaves can be removed, and the cuttings are direct planted into the soil at about half to two-thirds their length/depth.
- Another common way to grow Sweet Potatoes is by using whole tubers. The entire tuber is planted whole in the ground. This is an easy way to use your stored Sweet Potatoes.
- Finally, Sweet Potatoes are commonly propagated by using slips. “Slips” are sprouts with small roots that are removed from a tuber (i.e. “slipped off”) and planted as individual plants. These are easy to produce yourself….
- Just take a whole, half, or large chunk of Sweet Potato, poke some toothpicks in the side, and let the tuber sit about half in a cup/jar of water and half out. The shoots will grow out of the top. Once they are strong and healthy (about 8-10 inches/20-25 cm), the shoots can be slipped off (this takes a little practice) and placed in a cup of water, like a cut flower. Keep the water fresh, and roots will start to grow from the slip. Once the roots are about an inch long, they can be planted in place. Some sources state that these slips do not form as vigorous a root system as possible.
- Alternatively, the tuber can be covered in moist garden soil or sand. Keep the soil moist. Sprouts will appear just as above, and the slips may be placed in water above or in moist soil.
There are some relatives of Sweet Potato that are deadly poisonous. Just make sure you know what you are eating before you consume “wild” Sweet Potatoes.
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