Purple Sweet Potatoes are a recent addition to the North American Gardening realm. According to the LA Times, a sweet potato farmer in the Carolina's received some as a gift, and began growing them. They were later patented as Stokes Purple Sweet Potato.
However, they had been growing in the pacific region where they are believed to have originated. Some versions are called the Okinawa Sweet Potato, others the Hawaiian Sweet Potato. One thing is certain they are not-GMO and are heirlooms of exotic origins.
Purple Sweet Potatoes taste differs from traditional orange sweet potatoes and yams, it is not quite as moist but makes up for that with its rich texture and creamy yet subtle fruit flavor. Purple Sweet Potatoes still have that unmistakeable sweet potato taste, but picture if you will sweet potatoes blended with a tiny shot of wine.
Dr. Oz back listed them as a superfood.... "The women of Okinawa, Japan (who also happen to be the world's longest living ladies) enjoy a purple sweet potato they call imo every day for breakfast, lunch and dinner. Rich in beta-carotene and boasting 150% more antioxidants than blueberries, sweet potatoes are also super high in heart-healthy vitamin A. They're also packed with vitamin C to keep your immune system strong..." Dr. Oz's Favorite Superfoods
The flavanoid - antioxidant known as anthocyanin is a pigment found in many foods with a blue or purple hue and is effective in reducing cholesterol in addition to its anti-oxidant capabilities. Anthocyanin is what makes many "super foods" super.
Most Purple Sweet Potato varieties take a tediously long time to grow, a growing season of 140-160 days is needed to produce mature tubers. When they are harvested not fully mature the taste does not suffer, they still make a great swet potato - but they tend to be elongated and a tad scrawny. Plant in the same way you would standard potatoes or sweet potatoes, from slips or starts.
The Purple Sweet Potato slips require a warm environment to get going. If you live in a shorter season -cooler area it is a good idea to start them indoors. Place the slips in a glass of water, half of the potato should be above the waters surface. Using toothpicks to hold the slip in place works just fine.
Once they have sprouted they are plantable. Unlike with regular potatoes, you do not need to plant the entire sweet potato, although you can if you'd like. It is best to carefully separate the sprouts from the start - you should get several from each tuber.
Sprouts that you have been separated from the sweet potato are laid out in a bowl filled half way with water with the stem submerged. Root development from each sprout generally takes only a few days. Roots should be roughly an inch long before planting in soil. In short season regions it is best to plant them indoors to allow them to produce some healthy top growth before transplanting them into the garden.
Sweet potatoes need well-drained, non compacted soil to form the best tubers. The less resistance and obstacles the roots encounter, the better and bigger tubers it will yield. Loose soil is crucial.
After planting be sure to soak the bed thoroughly. Water them daily for the first two weeks but don't drown them. As the season progresses cut back on the water gradually till they are only being watered once a week towards season end. Excessive and persistent watering can lead to substandard mushy tubers as well as rots and fungi.
They are somewhat tolerant of drought, but naturally under extreme heat conditions you should bump up the water to curtail unnecessary stress on the plant. In warmer regions, where there is no hard frost they will over winter.