Barefoot Gardener: How Sweet It IsDecember 27, 2019, 6:00 AM HST (Updated September 8, 2020, 10:50 AM)
Known in Hawai‘i as ‘uala, sweet potatoes have long been an important food crop throughout Oceania. Endemic to South America and Africa, purple sweet potatoes (known as Okinawan sweet potatoes) and the common orange sweet potatoes of Hawai‘i underwent an interesting journey before arriving on these shores.
Christopher Columbus carried sweet potatoes from South America to the Orient, introducing them to China in 1525 and later to Japan in 1620. About the same time, Magellan brought the tubers to the Philippines from Western Mexico, then later to Japan. Sweet potatoes were subsequently introduced to Polynesia; they are believed to have first arrived in the Marquesas, eventually being transported to the Society Islands, Easter Island and Hawai‘i. Once in Hawai‘i, the growing of ‘uala was the only major agricultural endeavor in which women were known to participate.
Contrary to popular belief, sweet potatoes are not yams, though they are similar. Another lesser-known fact about sweet potatoes is that the attractive leaves and stem tips are edible, though there is a great deal of variation in flavor and culinary characteristics between varieties.
It is recommended that sweet potato leaves and stem tips be cooked, as some varieties may be slightly poisonous if eaten raw. The young leaves are the tastiest.
In Hawai‘i, most commercial sweet potatoes are grown around the 1,500- to 2,000-foot elevation. However, they will grow profusely just about anywhere in the Islands with the exception of very high elevations. There are two prevalent varieties of sweet potatoes grown here: the common sweet potato, Ipomea batatas, which is the variety that Columbus spread throughout Asia, and the Okinawan sweet potato, which boasts delicious purple meat.
A member of the morning glory family, sweet potatoes enjoy a slightly acidic (between 5.2 and 6.7 pH) sandy loam with clay subsoil, however they do quite well in a well-tilled clay soil that is amended with plenty of compost.
Generally, sweet potatoes are propagated from stem cuttings, though slices of the tuber buried straight into the garden or in a compost pile have been known to do quite well. Just recently, I discovered some ‘uala volunteers in my garden that sprouted just from some thin peelings I had randomly buried.
Plant six- to nine-inch long slips approximately four inches deep and about a foot apart. Planting in mounds or ridges is best, as it allows the sprawling vines room to ramble. If you are container gardening, planting in deep planter boxes that hang on a balcony railing provides room for the vines to trail and also creates an attractive foliage screen.
You’ll want to add a bit of phosphorus and potash, following the manufacturer’s directions for the amount per square footage of plantings. Be sparing with nitrogen, however, as too much will compromise root growth in favor of foliar proliferation. To simplify things, a good 0-6-6 fertilizer will do the trick. Make sure they have full sun and your sweet potatoes will usually mature in 120 to 180 days.