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What Are Purple Sweet Potatoes?
Purple sweet potato (Ipomoea batatas), also known as the Okinawan sweet potato, Hawaiian sweet potato, or Japanese yam, is a root vegetable similar to the white sweet potato, but with vibrant, deep purple flesh. The sweet potato’s purple color comes from anthocyanins, the same element in the soil that gives purple carrots and cherries their deep, plummy hues.
The purple sweet potato comes in a few different varieties—Charleston, Murasaki, and Okinawan. You can prepare each variety of purple sweet potato using several methods, including boiling, baking, mashing, roasting, and frying.
How to Make a DIY Potato Slip
Root vegetables like white potatoes and sweet potatoes are not grown from seed at all but from chunks of potato. Purple sweet potato slips are rooted cuttings of the potato vine that you can plant directly into your vegetable garden.
For DIY slips, find purple sweet potato (organic is best) at your local grocery store or farmers’ market. Cut halves of fresh sweet potato and soak the pieces in water, with half of the potato sticking out of the water (you can hold it in place with toothpicks). Keep the potato chunks in a warm spot until the green leafy bits begin sprouting. Next, twist off the sprouts, and soak the bottoms in water, with the top leaves hanging out above the water. Eventually, roots will form, and when they reach over an inch long, your sweet potatoes will be ready to plant.
How to Plant Purple Sweet Potatoes
Planting purple sweet potatoes can be challenging, as they require a long growing season (around 120 days), and consistent, hot weather. To grow your own purple sweet potatoes, check out the following steps:
- Choose a site. Sweet potatoes need at least six hours of full sun a day. While they can still grow in partial shade, the crop will thrive better with direct sunlight. Choose a planting site that receives at least six hours of sunlight per day.
- Dig your planting holes. You can grow sweet potatoes once the danger of frost has passed and your soil temperature reaches above 50 degrees Fahrenheit. Plant sweet potatoes in hilled rows, berms, or raised beds. Create your mounded rows of soil with planting holes approximately five to eight inches deep, and three to four inches wide.
- Plant. With the roots side facing down, bury your sweet potato slips in loose, well-drained soil, keeping the sprouted leafy part above ground. Fill the planting hole with soil and gently firm it with your hand to remove any air pockets.
- Water. During the first week of planting, water your mounds to thoroughly soak the dirt (but don’t water so much that the soil erodes). After the first week, water every other day, gradually tapering down the watering to once a week.
How to Care for Purple Sweet Potatoes
Purple sweet potatoes require little maintenance other than watering and pest control. Your potatoes won’t likely need fertilizer, but if you need to treat your soil, use a low-nitrogen fertilizer. Too much nitrogen in the soil will cause potato vines to grow rather than the tubers themselves.
Deer are big fans of sweet potato vines, so use mesh netting or wire cages to keep these critters from snacking on your crop.
How to Harvest Purple Sweet Potatoes
In warmer climates, it’s easier to tell when purple sweet potatoes are ready to harvest because their vines will yellow and die back. If you live in a cooler climate, harvest time will be shortly before the first fall frost (as early as 90 days, and as many as 120 days). When your tubers are ready, use a pitchfork or digging fork to loosen up the soil and dig out your potatoes with ease.
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