The Sweet Potato Explained

The sweet potato (Ipomoea batatas), known in Hindi as shakarkandi, is a trailing vine of the morning glory family whose thickened, starchy, sweet-tasting underground storage roots are eaten as a vegetable across India and the world. The sweet potato is grown in many Indian states, harvested mainly in the cooler months and best known in cities as the roasted winter street snack sold from smoking coal carts.

Although its name suggests a link with the ordinary potato, the sweet potato belongs to a different plant family and grows in a different way. This article explains what the sweet potato is, where it came from, how it is cultivated in India, the main types, how it is eaten and stored, and what it offers nutritionally.

Key Takeaways

• The sweet potato is the starchy storage root of Ipomoea batatas, a creeping vine of the morning glory family, Convolvulaceae.
• The sweet potato is not closely related to the potato (Solanum tuberosum), which belongs to the nightshade family, or to true yams, which belong to the genus Dioscorea.
• The sweet potato originated in tropical Central and South America and was introduced to India by European traders in about the 16th century.
• The sweet potato is propagated from vine cuttings and not from seed, and the crop matures in roughly three to five months.
• Orange-fleshed sweet potatoes are an important plant source of beta-carotene, the precursor of vitamin A, while purple types contain anthocyanin pigments.
• The sweet potato weevil is the most serious pest of the crop, and the roots must be cured and stored carefully to avoid rot.

What is a sweet potato?

A sweet potato is the thickened, starchy storage root of the plant Ipomoea batatas, a perennial vine usually grown as an annual crop for its sweet-tasting, nutritious roots. The roots vary in skin colour from white and cream to yellow, orange, red and purple, and the flesh may be white, yellow, orange or purple.

The plant is a creeping vine with heart-shaped or lobed leaves and funnel-shaped flowers, usually pale purple or pink, that look like those of its relative the morning glory. The vine spreads along the ground and roots at the nodes, forming a dense green cover that suppresses weeds.

In India the sweet potato is called shakarkandi in Hindi and many other languages, a word that combines “shakar”, meaning sugar, with “kand”, meaning root. Regional names include ranga alu in Bengali, sarkaraivalli kizhangu in Tamil and genasu in Kannada.

Is a sweet potato the same as a potato or a yam?

No, a sweet potato is not the same as a potato or a yam, because the three belong to different plant families and are separate crops. The sweet potato is in the family Convolvulaceae, the ordinary potato is in the nightshade family Solanaceae, and true yams are in the family Dioscoreaceae.

A potato is a modified stem, or tuber, while a sweet potato is a modified root, and this botanical difference is why a sweet potato can be grown from vine cuttings while a potato is grown from pieces of tuber. The confusion over the word “yam” is common, because in North America orange sweet potatoes are often labelled yams, whereas in India the name yam refers to different plants such as suran or elephant foot yam.

Where did the sweet potato come from and how did it reach India?

The sweet potato came from tropical Central and South America, where it was domesticated thousands of years ago, and it reached India through European traders, generally in the 16th century. It later spread across Asia and Africa and became a staple in many tropical countries.

The crop is also found in the Pacific islands, where it was grown long before European contact, and the details of how it crossed the Pacific are still discussed by researchers. For India, Portuguese and other European ships are the usual explanation for its arrival along the coasts, from where it spread inland because the vine cuttings are easy to carry and plant.

The sweet potato is one of the many American food plants, along with potato, tomato, chilli, maize and pineapple, that became part of the Indian diet after the 15th and 16th centuries. Over several centuries, farmers selected local forms, which is why India now has a wide range of skin and flesh colours.

How does the sweet potato plant grow?

The sweet potato plant grows as a trailing vine that spreads along the ground and produces swollen storage roots below the soil from roots that thicken as the plant stores food made by its leaves. A healthy vine can spread several metres in a season and produce a small cluster of roots under each plant.

Key features of the plant

• Vines: long, slender, green to purple stems that creep along the ground and root at the nodes.
• Leaves: heart-shaped to deeply lobed, green or purplish, and edible when young.
• Flowers: funnel-shaped, usually pale lavender, pink or white, and often not produced in all varieties or climates.
• Storage roots: spindle-shaped to rounded roots, usually three to six per plant, which form from fibrous roots and store starch and sugars.
• Climate needs: warm weather and a growing season free of frost; the plant is damaged by cold.

The crop does best in loose, well-drained sandy loam soils, with a slightly acidic to neutral pH. Heavy clay and waterlogged soil cause misshapen and rotting roots, and excess nitrogen makes the vines grow lush at the expense of the roots.

Where is the sweet potato grown in India?

The sweet potato is grown across India, and the notable producing states include Odisha, Uttar Pradesh, Bihar, West Bengal, Gujarat, Madhya Pradesh, Assam and Karnataka, as well as parts of Kerala, Tamil Nadu and the northeastern hill states. Exact rankings vary from year to year, so state shares are best described only in general terms.

The crop is typically grown by small farmers on a modest area compared with cereals, and it is often raised on river banks, sandy soils and marginal land where other vegetables do not do well. The tribal and hill regions of Odisha and the northeast are important growing areas, where the crop is a useful source of food and cash.

Research on the crop in India is led by the ICAR-Central Tuber Crops Research Institute (CTCRI) at Thiruvananthapuram, Kerala, which has a regional centre at Bhubaneswar in Odisha. The institute has released improved varieties, including orange-fleshed and purple-fleshed types, and works on pest management and seed production.

How is the sweet potato cultivated in India?

The sweet potato is cultivated by planting cuttings from healthy vines, about 20 to 30 cm long, on ridges or mounds, and it is ready for harvest in about three to five months. Seed is not used, so planting material is taken from vine tips, which carry fewer weevils and diseases than older vines.

The main steps

• Land preparation: the soil is ploughed to a fine tilth and formed into ridges or raised beds to give good drainage and room for roots to swell.
• Planting: vine cuttings are planted on the ridges, usually with the monsoon from about June to August, or in the cooler months in some regions with irrigation.
• Nutrition and water: moderate fertiliser, with enough potash, and irrigation at intervals; too much nitrogen or water reduces yield.
• Earthing up: soil is pulled up around the plants to cover the developing roots and discourage weevils.
• Harvest: roots are dug when the leaves begin to turn yellow, taking care not to cut or bruise them.

Farmers often turn over the vines during growth to prevent them from rooting at every node, since this stops the formation of many small roots. After harvest, the vines are usually fed to cattle as fodder, so the crop gives both food and feed.

What are the main types and varieties of sweet potato?

The main types of sweet potato are classified by flesh colour into white or cream, yellow, orange and purple, and each type has different taste, texture and nutritional features. Many Indian varieties have been developed by ICAR institutes, and local landraces are also widely grown.

The orange-fleshed varieties have drawn special attention in India as a way to help address vitamin A deficiency, because they supply beta-carotene at low cost. Biofortified varieties are promoted by research institutes and nutrition programmes. Varieties differ in maturity time, yield and storage quality, so farmers choose them according to local conditions and market demand.

How is the sweet potato eaten in India?

The sweet potato is eaten in India roasted, boiled, steamed or fried, and the most familiar form is shakarkandi roasted in hot coals or in a drum oven and sold by street vendors in winter. It is typically served peeled and cut into pieces, sprinkled with rock salt, chaat masala, lemon juice and sometimes chilli powder.

• Roasted or boiled snack: a winter street food in many northern cities, usually served warm in a paper cone.
• Fasting food: sweet potato is permitted on many vrat or fasting days, such as during Navratri, and is made into chaat, boiled dishes and light curries.
• Curries and stir-fries: used in vegetable dishes and mixed with other roots in some regions.
• Sweets: cooked into halwa, kheer and other desserts, and the purple type is used for colour.
• Leaves and shoots: tender leaves are cooked as greens in some parts of India, especially in the northeast and the south.
• Fodder and industry: vines feed cattle, and roots can be processed into starch, flour and chips.

The sweet taste of the roots increases with cooking, because heat activates enzymes that turn some starch into the sugar maltose. Slow roasting therefore gives a sweeter, more caramelised flavour than quick boiling.

What nutrients does the sweet potato provide?

The sweet potato provides carbohydrates for energy, dietary fibre, vitamin C, potassium and, in orange-fleshed types, large amounts of beta-carotene, which the body converts to vitamin A. The roots are low in fat and protein, so they are best eaten with other foods that supply protein.

Orange-fleshed sweet potatoes get their colour from carotenoids, and a typical serving can meet a large part of a person’s daily vitamin A needs. Purple types contain anthocyanins, which are plant pigments that act as antioxidants. The skin adds fibre, so washing and cooking the root with the skin on is a good way to retain nutrients.

Sweet potatoes contain natural sugars but are digested more slowly than many refined foods, and the way they are cooked affects how quickly their sugars are absorbed. Boiled or steamed roots generally raise blood sugar more slowly than baked or roasted ones. People who manage diabetes should follow their doctor’s advice about portion size.

What pests and problems affect the sweet potato?

The most serious pest of the sweet potato is the sweet potato weevil, Cylas formicarius, whose larvae tunnel into the roots and vines and make the roots bitter and inedible. Viral diseases, fungal rots and poor planting material are other common problems.

• Sweet potato weevil: adults feed on leaves and vines, and larvae bore into roots, a problem that worsens in dry weather when soil cracks.
• Virus diseases: several viruses spread by whiteflies and aphids stunt plants and reduce yield, and they pass on through infected cuttings.
• Fungal diseases: leaf spots and storage rots, including black rot, damage plants and harvested roots.
• Handling damage: cuts and bruises at harvest let rot organisms enter, shortening storage life.

Farmers manage these problems with clean vine-tip cuttings, crop rotation, earthing up soil to cover the roots, timely harvest and careful handling. Resistant varieties and integrated pest management help reduce losses and the use of chemical sprays.

How should sweet potatoes be stored?

Sweet potatoes should be stored in a cool, dry, dark and well-ventilated place and not in the refrigerator, because cold causes the roots to develop a hard core and an off flavour. Roots that are handled gently and kept dry usually last several weeks at room temperature in the cooler months.

Commercial handlers cure the roots after harvest by keeping them for several days at warm temperatures and high humidity, which heals small wounds and thickens the skin. Cured roots keep longer and also taste sweeter. Small farmers often rely on simpler methods, such as storing roots in dry sand, in pits or in well-aired rooms.

Roots with soft spots, mould or a bitter smell should be discarded, since the bitterness can come from weevil damage or from stress compounds the root produces when injured.

Bottom Line

The sweet potato is the sweet, starchy storage root of a creeping vine from tropical America that became a well-loved Indian crop and winter snack. Easy to grow from vine cuttings, nutritious and adaptable, it provides food, fodder and, in orange-fleshed varieties, a valuable plant source of vitamin A.

Frequently Asked Questions

What is a sweet potato?

A sweet potato is the starchy, sweet-tasting storage root of Ipomoea batatas, a trailing vine of the morning glory family. Its skin and flesh can be white, yellow, orange or purple. It is called shakarkandi in Hindi and is eaten roasted, boiled or cooked in many dishes.

Is a sweet potato the same as a yam or a potato?

No, the sweet potato is a different plant from both the potato and the yam. The potato is a stem tuber of the nightshade family, true yams belong to the genus Dioscorea, and the sweet potato is a root of the morning glory family. In India, the word yam usually refers to other crops such as suran.

Which Indian states grow sweet potato?

Sweet potato is grown across India, with Odisha, Uttar Pradesh, Bihar, West Bengal, Gujarat, Madhya Pradesh, Assam and Karnataka among the notable producing states. Parts of the south and the northeastern hills also grow the crop. Exact state rankings change from year to year.

How long does sweet potato take to grow?

Sweet potato usually takes about three to five months from planting vine cuttings to harvest, depending on the variety and the climate. Early-maturing varieties are ready sooner. The roots are dug when the leaves begin to yellow.

Is sweet potato healthy?

Yes, sweet potato is a nutritious food that supplies carbohydrates, fibre, vitamin C and potassium, and orange-fleshed types are rich in beta-carotene. Its nutritional value is best retained when it is boiled, steamed or lightly roasted with the skin. People with diabetes should check portion sizes with their doctor.

Why should sweet potatoes not be kept in the fridge?

Sweet potatoes should not be kept in the fridge because cold temperatures damage the roots, producing a hard centre and a poor flavour. They keep best in a cool, dry, dark and ventilated place at room temperature. Cut or cooked pieces can be refrigerated for a few days.

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