Sweet potatoes grow like weeds!

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Sweet potato crop. Image by Chang Min SHIN from PixabaySweet potato crop. Image by Chang Min SHIN from PixabaySweet potatoes are extremely easy to grow at home in garden beds or containers. They make beautiful foliage plants which can be placed on a sunny patio and trained up a trellis. Their lush foliage also makes them lovely indoor pot plants. Here's everything you need to know about growing your own delicious and nutritious sweet potatoes.

For South Africans sweet potatoes are the traditional “soet patat” or batata, and because they thrive in hot summer conditions and are so easy to grow, they could almost be classifies as weeds. And, there's no denying the beauty of a sweet potato plant, whether it's placed where it can creep up a trellis or is grown in a garden bed as a groundcover, or as a simple container plant, its foliage is quite beautiful. And when it comes to its health benefits, sweet potatoes are well worth adding to your diet as they are loaded with vitamins, minerals, fibre, and phytonutrients that can bolster your body and mind.

The origins of sweet potatoes are shrouded in the mists of time, and although it is generally accepted that they originated in Central and South America, and we are taught in school that  Christopher Columbus and his European compatriots are responsible  for spreading many foods like tomatoes and chilli peppers, as well as sweet potatoes  around the world, many anthropologists think that a few foods made the vast trek across the Pacific Ocean long before Columbus landed in the New World, and their proof is in the sweet potato.

Sweet Potato'Beauregard' Picture courtesy LivingseedsSweet Potato'Beauregard' Picture courtesy LivingseedsArchaeologists have found prehistoric remnants of sweet potato in Polynesia dating from about A.D. 1000 to A.D. 1100, according to radiocarbon dating, and these archaeologists hypothesized that these ancient samples originally came from the western coast of South America. Among the clues were the names for sweet potatoes as the Polynesian word for sweet potato "kuumala" resembles "kumara," or "cumal," the words for the vegetable in Quechua, a language spoken by Andean natives.

For a very long time there was little genetic proof for this theory, partly because modern sweet potatoes are a genetic muddle - a hybrid of different cultivars that Europeans helped spread around the globe - so it's hard to decipher their origins from their DNA. Caroline Rouiller, an evolutionary biologist, got around this problem by turning to dried sweet potato remains preserved in a London museum, which Captain James Cook's crew picked up in Polynesia back in 1769, before all this interbreeding took place. Examining the genetic blueprint of these sweet potatoes allowed Rouiller and her colleagues to trace the root's evolution all the way back to Ecuador and Peru.

These clues naturally led to the question “how did the sweet potato travel 5,000 miles across the vast Pacific Ocean?” It is surmised that the seeds could have possibly hitched a ride on seaweed or gotten lodged in the wing of a bird, but Pat Kirch, an archaeologist at the University of Berkeley, California, thinks the Polynesians were well-equipped to sail right across the Pacific to South America, and he states that there is a lot of new evidence that the Polynesians made landfall in South America, and that it is highly possible that they had sophisticated double-hulled canoes much like very large catamarans which could carry 80 or more people and be out to sea for months. For those who like to study history there are many articles online on this subject, but no matter what you believe, today no one can dispute the popularity of sweet potatoes, and this warm-weather crop grows worldwide, from tropical regions to temperate climates.

Sweet potatoes come in two different varieties - dry flesh types and moist flesh types. The moist fleshed types convert more starch to sugars when cooked, thus becoming softer and sweeter than their dry kin and are often referred to as yams, although true yams can only be cultivated in tropical climates. Either variety has roots variously hued from white to orange or red, depending on the cultivar.

In South Africa the major commercial production areas are in Limpopo, Mpumalanga, KwaZulu-Natal and the Western Cape.

Sweet Potato 'Bophelo' Picture courtesy LivingseedsSweet Potato 'Bophelo' Picture courtesy LivingseedsHealth Benefits:

The orange and red-fleshed types are rich in beta-carotene, a pro-vitamin A carotenoid that is converted to vitamin A by the human body, and for this reason they are grown to alleviate vitamin A deficiency in many parts of the world, including Sub-Saharan Africa, and South and East Asia. In South Africa, this food source is of great importance as a recent survey indicated that 43.6% of children aged 1 to 5 years, and 27% of women of reproductive age, are deficient in vitamin A, a level which is considered as a serious public health problem.

Sweet potato is an excellent source of carbohydrates and has a low glycaemic index (GI) because they take time to digest and so keep blood sugar constant.

Sweet potatoes are remarkably nutritious and are also rich in vitamins B6 and C, along with many other important minerals like iron and magnesium. Including them regularly in your diet can help prevent heart attacks, boost the immune system, protect the body against toxins, and improve the metabolism.

Sweet Potato Cake. Image by la fontein PixabaySweet Potato Cake. Image by la fontein PixabayIn the Kitchen:

Use sweet potatoes grated raw, boiled, or baked, in soups, casseroles, desserts, breads, or stir-fried, and for a delicious treat make some homemade sweet potato fries!

There are many exciting ways to use your sweet potatoes in the kitchen and one classic favourite that will please adults and children alike is 'Candied Sweet Potatoes' which are often served in America for Thanksgiving and Christmas. This dish is easy to make and many recipes are available online, often including brandy. And for those with a really 'sweet tooth' Thanksgiving isn't complete without a homemade sweet potato casserole, topped with marshmallows and toasted pecans.

Savoury recipes include: 'Twice Baked Sweet Potatoes with Ricotta Cheese' where baked potatoes are scooped out and blended with ricotta, salt, pepper, and sugar (optional) until smooth, before adding finely sliced spring onions or shallots and placing the pulp back into the shells, then sprinkling Parmesan cheese and freshly chopped sage on top before popping them back into the oven to finish them off - delicious!

'Slow-Cooker Vegetarian Chilli with Sweet Potatoes' is a delicious dish where sweet potatoes are used to bulk-up  vegetarian chilli with lots of sweet potatoes and veggies like red onions, bell peppers and tomatoes. To round it out, add two different kinds of beans. This sweet potato chilli has staying power, whether it’s for a weeknight dinner or a crowd-pleasing main course.

'Sweet Potato and Kale Frittata' is perfect for breakfast, lunch, or dinner; and 'Sweet-and-Spicy Chicken with Roasted Sweet Potatoes and Asparagus' is an easy weeknight dish which is packed with flavour, and the leftovers taste delicious reheated or cold. 'Bean and Corn-Stuffed Sweet Potatoes' is the ultimate filling yet quick and easy lunch or dinner meal. Microwave or bake the potatoes, top with beans, greens, cheese and spices, and voilà, a happy and full tummy is guaranteed.

Explore the multitude of yummy dishes using sweet potatoes online to find the perfect ones for your family.

Uses:

Sweet potatoes may be not as popular as other vegetables like potatoes and tomatoes, but they still play an important role in South Africa in terms of food security and alleviating malnutrition. Sweet potato is grown by many resource-poor farmers in virtually all provinces of South Africa. Because they are very nutritious, the leafy vines are used by rural farmers feed to their stock, and the tubers that cannot be sold or eaten because they are damaged or too small or cracked, can also be used as stock feed.

Sweet Potato 'Variety Hamper' Picture courtesy LivingseedsSweet Potato 'Variety Hamper' Picture courtesy LivingseedsIn the Garden and Home:

If you're curious about growing sweet potatoes at home, keep in mind that they do best in a sunny position. They can be grown in the vegetable garden and can even act as a temporary groundcover. They also look beautiful climbing up a trellis or trailing down a pot on the patio, where the vine will form a gorgeous foliage plant that you can harvest in autumn by tipping the pot over to remove the tubers. The plant can even make a glorious trailing houseplant, so no matter how much space you have available most folks can grow some sweet potatoes.

Companion Planting:

Root vegetables, such as parsnips and beets, are good sweet potato companions, and bush beans also make good companions. Regular potatoes, because they are not actually closely related at all to sweet potatoes also make good companions.

Aromatic herbs like thyme, oregano and dill, are great with sweet potatoes, and to deter the sweet potato weevil plant summer savoury nearby.

Be aware that your sweet potato vine will grow to cover a large area, so take care that it doesn’t crowd out its beneficial neighbours. For this reason pumpkin and squashes, which also spread widely, do not make good companions for sweet potatoes.

Cultivation/Propagation:

Although the sweet potato is a perennial plant in its native environment, in South Africa it is treated as an annual summer crop because it cannot tolerate cold and frost. The plant requires plenty of sunlight, with hot days and warm nights, with very few cold, cloudy days. The flesh is classified as either moist or dry, and the moist, deep orange types which are sometimes called yams, are more popular with home gardeners.

Depending on the cultivar grown, sweet potatoes have a growing season of 3 to 5 months, and planting should preferably take place from October to December. In frost-free regions planting can continue up to about March.

Sweet potatoes can be grown on a wide variety of soils and thrive on fairly deep, sandy loam which drains well. Heavy clayey soils are not recommended as they may produce misshapen roots (tubers) and cause tuber rot. Very rich soils which contain a large amount of organic material are also not suitable, because the plant will produce very lush top-growth at the expense of the tubers which will be long and thin. For this reason fresh compost or manure should not be worked into the soil immediately before planting.  In very poor, sandy soils the tubers will also be long and stringy.

Sweet potatoes are usually propagated by means of rooted shoots or vine cuttings, and unfortunately for the average gardener or small-scale farmer there are not many commercial sources of cuttings. Livingseeds supplies them to the public but orders need to be placed in advance for planting from September to November. Luckily sweet potatoes are easily grown from a few well-shaped, disease-free tubers bought from the store or local farmers market, or you could get a few runners from a friend who is growing them.

Plant the tubers closely together in a seedbed, cover them with a 5cm layer of soil, and water moderately until the shoots appear, after which watering can be increased. When the shoots are about 20 to 30cm long they are ready for planting out, and the shoots are then simply tugged gently or cut off of the tubers. Cut off a small portion at the bottom of each slip before planting as that portion sometimes harbours disease organisms. Carefully plant them up to half their length into the soil, gently firming it down and watering well afterwards.    

It is possible to plant the crop successfully on level soil and then simply allowing it to spread as a groundcover, but better yields are obtained by planting on top of  flattened ridges, about 25cm high. Space the ridges about 90cm to 1m apart, and space the shoots 30cm apart. The closer the spacing, the smaller the tubers will be. 

To smother weeds, conserve moisture, and keep the soil loose for root development, mulch the vines two weeks after planting. As the plants grow, draw up soil to the main stem to ensure a good yield and to prevent the sweet potato weevil from reaching the roots through cracks in the soil. Keep the beds free of weeds which can harbour pests and diseases.

Often the crops are grown between black plastic sheeting to keep weeds at bay and to prevent them from continually rooting as they spread along the ground, but if you are growing them on open soil it is advisable to occasionally lift the longer vines to prevent them from rooting at the joints, or they will put all their energy into forming many undersized tubers at each rooted area rather than ripening the main crop at the base of the plant. Otherwise, handle the plants as little as possible to prevent wounds that make them vulnerable to disease spores.

Although sweet potatoes are fairly drought resistant, if the weather is dry, water moderately to ensure a good yield, but do not overwater, or the plants may rot. About two weeks before harvesting, reduce the amount you water and allow the soil dry out a bit.

Sweet Potato 'IPC Yellow' Picture courtesy LivingseedsSweet Potato 'IPC Yellow' Picture courtesy LivingseedsHow to Grow Sweet Potatoes in Containers:

If space is limited you will be glad to know that sweet potatoes grow easily in containers of all sorts and grow bags are available from garden centres. These bags are designed specifically to provide aeration to the roots, adequate drainage, and some even have side pockets so you can sneak a small spud here and there. When your sweet potatoes are ready to harvest, you simply lift the bag and dump the contents out onto the ground or into a wheelbarrow, making harvesting extremely easy. Grow bags can be re-used and are easy to store in the winter because of their collapsible nature, making them very economical in the long run. Many gardeners have also had great success when using whiskey barrels as well as clay containers. If you can, for pot culture, select varieties which are more compact in their growth habit.

Sweet potatoes love to remain moist, but do not like to sit in water. Therefore it is important to have a good soil mix which drains well while still retaining moisture. Therefore, when planting in containers, using a container mix amended with compost, some washed river sand, and a fertiliser for vegetables is ideal. Place gravel or pebbles at the bottom for drainage then add about 10cm of soil to cover them before planting your sweet potato slips. Then add just enough soil to secure the cuttings firmly and water well.

Once planted, make sure to water regularly. Water frequency depends upon the type and size of container selected. If you are using a grow bag which is porous, it causes the soil mix to dry out quicker than it would in a clay or wooden container, so check the soil daily and water if dry. If fertiliser was not included in your original mixture, two weeks after planting, feed with a fertiliser for vegetables. As the stems grow upward, continue to add more of your soil mix until the level reaches the top of the container.

Sweet Potato 'Ndou' Picture courtesy LivingseedsSweet Potato 'Ndou' Picture courtesy LivingseedsHarvesting, Curing and Storing:

Sweet potatoes can be harvested as soon as the roots are large enough, usually 3 to 5 months after planting, depending on the cultivar. A good indication that they are ready to be harvested is when the ridges crack open because of the swelling roots. You can also start harvesting as soon as leaves start to yellow, but the longer a crop is left in the ground, the higher the yields will be. Once frost blackens the vines, however, the tubers can quickly rot. If the vines are still green but the crop needs to be harvested, they can be cut off, but not earlier than 2 to 3 weeks before harvesting. This makes it easier to lift the tubers.

Dig the tubers out on a sunny day when the soil is dry, using a garden fork to lift them,  and remember that tubers can grow a 30cm or more from the plant, so ensure you collect them all. Be very careful not to damage the tubers as any nicks on their tender skins will encourage spoilage. Damaged tubers should be used as soon as possible.

Sweet potatoes do not store very well unless they are well cured, so if you have a small crop, lift only as many as you need every time. Do not wash the tubers but rather brush the soil off and then dry the tubers in the sun for several hours before moving them to a warm and dry, well-ventilated spot to cure for 10 to 15 days. After they are cured, store in a cool place at about 13 to 16°C with a humidity of 75 to 80%. Properly cured and stored sweet potatoes will keep for several months.

A 3.5m row will produce about 3 to 4.5kg of potatoes, and if you have a large enough crop to sell, cure the roots by placing the tubers in small heaps on the land for about 7 days to dry off, covering  them lightly with vines to prevent sun damage.

Problems, Pests & Diseases:

Sweet potatoes are generally not bothered by many pests and the sweet potato weevil is the most serious pest affecting crops around the world. The adult beetle measures 5.5 to 8mm in length and appears smooth and shiny, but upon close examination shows a layer of short hairs. It is striking in form and colour, and the body, legs, and head are long and thin, giving it an ant-like appearance. The head is black, and the antennae, thorax and legs are orange to reddish brown; and the abdomen and elytra are metallic blue. The snout is slightly curved and the antennae are attached at about the mid-point on the snout.

Adults are secretive and are not readily noticed, often feeding on the lower surface of the leaves and stems of sweet potatoes, and quickly feign death if disturbed. Adults can fly in short, low flights, but rarely seem to do so. However, because they are active mostly at night, their dispersive abilities are probably underestimated. Females feed for a day or more before becoming sexually active, after which they puncture the stems and tubers of their host plant to lay their eggs. Developing larvae tunnel and feed on the fleshy roots, while adults generally attack the vines and leaves. They also spread foot rot, which creates enlarging brown to black areas on stems near the soil and at stem ends. Since weevils multiply quickly and prove hard to eliminate, try to plant certified disease-resistant slips and practice a four-year crop rotation. Destroy infected plants and their roots, or place them in sealed containers and dispose of them with your household trash.

Fungal diseases include black rot, which results in circular, dark depressions on the tubers, which should be discarded. Don't confuse this disease with less-serious ‘scurf’, which creates small, round, dark spots on tuber surfaces but doesn't affect eating quality.

Stem rot, or wilt, is a fungus that enters plants injured by insects or by careless cultivation, or wind. Even if this disease does not kill the plants, the harvest will be poor. Minimize the chances of disease by planting only healthy slips; and avoid black and stem rot by planting resistant cultivars. Reduce the incidence of dry rot, which mummifies stored potatoes, by storing the fleshy roots at the correct temperature.