When most people think about sweet potatoes (Ipomoea batatas, USDA hardiness zones 9-11), Thanksgiving dinner comes to mind. It's pretty easy to love a sweet potato casserole, as these tubers are edible as a daily starch. Packed with fiber, vitamins and minerals, sweet potatoes are a delicious root vegetable and they are fairly easy to grow in zones 9 and warmer, where they're perennial. However, they can also grow in cooler zones if you make a few adjustments and prep the plants well ahead of time. They need at least 90 days to mature; some require 120 or more.
Where to Grow Sweet Potatoes
Sweet potatoes love warm weather and must be planted in soil that is at least 70 degrees Fahrenheit. They are perfect for growing outside in places like the South that have long, hot summers, but you can plant them in colder climates if you take the time to warm the soil or plant slips or seedlings.
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If you live in a Northern state where the soil won't be 70 F in June, you can warm the soil by covering it with plastic. Buy black plastic mulch and anchor it in the ground where you plan to plant your sweet potatoes. In a colder climate, raised garden beds work even better than planting in the ground because it's easier to warm up the soil in contained beds. If your planting area gets direct sun, the soil should warm up fairly quickly. No matter the climate, make sure you plant your potatoes after the last frost. Ideally, sweet potatoes need eight to 10 hours of direct sun daily.
Grow and Prepare 'Slips'
Most sweet potatoes are grown using slips, small sprouts from a sweet potato. Ideally, it's best to purchase these slips, which are certified disease-free. But if you're using store-bought sweet potatoes, be sure to buy organic. Nonorganic ones may have sprout-suppressing chemicals and ingredients. You also want to check store-bought sweet potatoes for cold damage. This can show up as dark lesions and spots on the skin. You can grow your own slips by placing the wide end of a sweet potato in a water glass or canning jar. Stick a toothpick in each side of the potato to hold it up when it's placed into the glass. After a couple of weeks it will sprout and slips will grow.
The next step is to twist each slip out of the potato and then put them in a glass of water in bright light but out of direct sun. After another two weeks, the slips will have roots. Now the slips are ready to be planted outside. If you have a short growing season, transplant the slips after they've become seedlings.
If you want to keep things simple or you didn't give yourself enough time to grow your own slips, you can also order slips or buy them from garden centers.
Plant the Slips
When the roots have grown in, it's time to plant your slips in soil. Space them about 3 feet apart so there is room for each plant to expand beneath the soil. These plants do best in slightly acidic soil and don't like overly dense clay soil. If there is clay in your soil, loosen it by incorporating organic matter into the planting area. Or consider planting the potatoes in raised beds so you can mix your own soil.
If you're planting potatoes in a Northern climate, cut slits into the plastic that's been warming the soil and plant the slips in those spaces.
Caring for Your Sweet Potatoes
Water the crop thoroughly either in the early morning or late evening for the first two weeks. The plants will need at least 1 inch of water each week, especially when they are first planted and establishing their roots. Three to four weeks before you harvest them, stop watering. This will prevent the tubers from splitting.
Sweet potatoes produce beautiful vines on top of the earth while the tubers grow beneath the soil. Weed around these vines, but do so carefully so you don't disrupt the tubers underneath.
The Harvest and Curing Process
Sweet potatoes typically are ready to harvest 90 to 120 days after planting; some even take as long as 170 days. Definitely dig them up before the first frost. After you've harvested your sweet potatoes, don't eat them right away. They won't hurt you, but they won't taste very sweet. Like fine wine, sweet potatoes need to age a bit or "cure."
Allow the potatoes dry in a shady, warm location. You want the temperature to be about 80 to 85 F but not sunny. Leave them there for several days up to two weeks, and then you can move them to your kitchen, perhaps in the pantry. The temperature should be above 55 F, so a refrigerator isn't suitable. You can keep these potatoes for up to six months.
After they've been moved inside, it's time to feast. Enjoy your bounty and the satisfaction of eating something healthy that tastes delicious and that you grew all by yourself.
One thing to note is that there are two types of sweet potatoes: ornamental and edible. While both are technically edible, the texture and flavor of ornamental sweet potatoes are not as appetizing.