4/5 – Moderate (3-4 months as leaves die, but well worth the wait)
4/4 – Very tender (can’t take light frost)
Most Problematic Nemesis:
Nothing too serious
No – produces tubers away from main base
There isn’t much mention of sweet potatoes in most gardening books, yet it is extremely easy to grow and the harvest is bountiful. These tubers can be eaten baked, boiled or candied – even alcohol can be made from sweet potatoes. Young shoots and leaves are sometimes eaten as greens or given to livestock. Given enough space, sweet potatoes grow vigorously and produce a lot of tubers, but they may take over the garden if not kept in check!
It is generally assumed that the sweet potato has its origins in tropical America, specifically from wild Mexican Ipomoea trifida. It may have been cultivated since 8000BC in Mexico, Central and South America, and the West Indies. Columbus returned from his first voyage to the New World to Spain with the sweet potato. Thereafter the Spaniards and Portuguese transported it to Asia and Africa, and by some way it was transported to Polynesia and New Zealand as well. Lately, it is an important root crop in Asia and Africa, but is also cultivated in the Americas and Europe.
The Sweet Potato, Ipomoea batatas, belongs to the Convolvulaceae (the morning glory family) and is often confused with yams (Dioscoreaspp.) and is not a true potato (Solanum tuberosum). There are ornamental varieties, which are called tuberous morning glories, which to my mind it a better definition for the root crop.
There are different varieties of sweet potato, elongated to globular, white, tan, yellow, red, purple skinned and ones with white, yellow or orange flesh.
Ipomoea trifida, and some other wild sweet potato varieties are still bred into the domesticated lineage, as these varieties have high genetic diversity and their tubers contain more starch.
Growing Sweet Potatoes
So the one big thing I read on sweet potatoes is that it does not tolerate frost, considering that it is a subtropical to tropical crop. Therefore it should be grown in regions with five months (or more) worth of growing season. Cold tolerant cultivars have been introduced to the UK, but it still requires the protection and added heat from tunnels, frames or green houses to crop reliably.
It prefers temperature above 24oC (75oF), but will tolerate temperature as low as 15oC. It likes lots of sun and warm nights. Apparently it likes a lot of water and is sensitive to drought, although mine did not have the slightest problem with this – the tomatoes are more thirsty that the sweet potato! Water-logging may cause the tubers to rot, but there is no such threat in SA
It will appreciate some compost and produce larger crops, but it can cope with poor soils and many farming conditions. The sweet potato requires little weeding, as it is a weed itself, excluding all other weeds (although mine was able to co-habituate with some miss-placed potato plants). Make sure that the soil is loosened up to 25cm for tubers to form properly.
Other sweet potato tips
Make sure to keep an eye on its trailing nature as it will creep into everything and needs to be restricted if grown amongst other vegetables, else you can plop it somewhere in the garden and let it carry on.
The plant does not have problematic pests or diseases, I had a few caterpillars feeding on its foliage, but luckily my wasp army made off with the invasion soon enough 😉
Golden, orange or jewel sweet potatoes are more resistant to millipede damage (holes eaten into tubers, especially pronounced during droughts)
Harvesting and Storing
Sweet potatoes are harvested once the leaves start to yellow, usually 4-5 months after planting. Leaving the tubers in the soil after the plant has died ensures that the starch content increases and the tubers become sweeter, but the tubers must be harvested before the first frost.
Sweet potatoes need proper curing to become sweet and moist. This can be done by storing them in a warm (26oC, 80oF) and humid room with good ventilation for 5-10 days. Afterwards the sweet potatoes can be stored at 12-15oC (55-60oF). To low temperature causes root to harden, whereas to high and dry conditions cause roots to shrivel. So I suggest storing them in a paper bag to level out the conditions a bit more. Properly cured sweet potatoes can keep for up to 12 months, just check them regularly for any signs of disease or rot.
Sweet potatoes do best when grown vegetatively- that being cuttings or ‘slips’. Cuttings of sweet potato vine root easily and rapidly in water. Slips are similar to potato ‘eyes’; half of the tuber can be placed into a cup of water and left in the water until the tuber produces shoots, after which it can be planted into the garden.
I suppose you can get sweet potato plants/cuttings and a nursery, but no such luck here. I let some store-bought sweet potatoes produce slips and planted them in the garden.
As with the potatoes, keep some smaller tubers to produce slips in the next season.
My Sweet Potatoes
So, again, as with the potato – I don’t have a ‘formal’ sweet potato cultivar. I have made slips from white and orange flesh varieties. You will notice that some of your sweet potatoes will grow slower than the others (and they’ll have leaves that curl inwards), these are poor stock and their smaller tubers should rather not be kept as slips for the next season.