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How to Grow: Sweet Potatoes
Learn about sweet potatoes, including how to plant and grow this vegetable.
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Now here’s a vegetable you normally don’t think of growing in the Northeast, but you actually can. Sweet potatoes (Ipomoea batatas) are a traditional Southern crop and need heat and a long season (up to 4 months) to form potatoes. However, with a few tricks, I’ve been able to grow good-sized sweet potatoes even in Vermont, so it is possible.
The keys with growing sweet potatoes in our sometimes cool summer climate is to get them off to a good start, keep the plants well watered and fertilized, and keep the soil warm. Beside being tasty baked, mashed, or in soups and pies, sweet potatoes are high in vitamin A and fresh tubers dug from your garden are much tastier than anything store bought. Plus, they’re an attractive ground cover. Some varieties are sold for their beautiful leaves as ornamentals, not their edible tubers.
When to Plant
Unlike most other vegetables, sweet potatoes are planted from little plants or “slips”. While you can grow your own slips, it’s much easier to buy them locally or order them through the mail and they will be certified disease free. You need to wait until the soil has warmed to 65F, at least 2 weeks after your last frost date, to plant. That’s late May or June in most areas.
Where to Plant
To get a good crop, sweet potatoes need lots of sun and warmth. plant them in the hottest place in your garden. They also need well drained soil, so build a 8-inch tall raised bed a 2 weeks before planting and lay black plastic mulch on it to preheat the soil.
How to Plant
Amend the soil with compost prior to building the raised bed. Plant slips in holes poked in the plastic 1 foot apart in rows 3 feet apart for bush varieties and 4 feet apart for vining varieties. Place a small handful of an organic fertilizer, such as 5-5-5, in each planting hole.
Care and Maintenance
Cover the planted slips with a floating row cover during any cool nights. Once the vines begin to grow or “run”, mulch the pathways with a layer of an organic mulch such as straw or untreated grass clippings. Although sweet potatoes are somewhat drought tolerant, keep the young plants well watered until they’re established. Stop watering a few weeks before harvest to avoid rotting the roots.
Sweet potatoes don’t have many pest problems. Rotate crops, not growing sweet potatoes in the same area for 3 years, to avoid diseases. Don’t plant in an area that was recently lawn to avoid wireworms tunneling holes in the tubers.
Sweet potatoes can be a bit mysterious to know when to harvest. Start checking for tubers about 3 months after planting. Look for signs of leaves yellowing, too. Gently lift the plants out of the ground before the cool weather of autumn begins. They won’t grow much during cool temperatures and the longer the tubers are in the ground, the more likely they will get attacked by wireworms or other pests.
Don’t eat them immediately or you’ll be disappointed. Cure the tubers in a warm, high humidity room for two weeks so the skins toughen. Store them in a dry, 60F room for at least 6 weeks before eating. During that time the starches will turn into sugar, creating the sweet tubers we all love. They can store for up to 6 months.
‘Beauregard’ is a fast maturing vining type with red skin and moist orange flesh. ‘White Yam’ is a white skin and dry-fleshed vining variety. ‘Bush Porto Rico’ has red flesh that turns yellow when ripe.
Excepted from the Northeast Vegetable and Fruit Gardening book.
Sweet potatoes are not a vegetable you normally think of growing in Vermont, but you can. It’s a warm weather lover that also makes an attractive ground cover. There are a number of ornamental sweet potato vines available exclusively grown for their foliage. They do produce edible tubers, but if you want good flavor, try the ‘Beauregard’ variety.Sweet potatoes grow best on a well-drained, loose soil amended with compost. Lay black plastic mulch over the garden area two weeks before planting. Transplant your locally purchased sweet potato slips after all danger of frost has passed. Let them grow all summer keeping them well watered.
Once the foliage yellows, but before frost has blackened the vines, start harvesting. If you wait too long they may rot in the ground. Wait for a dry day and with a shovel or iron fork carefully dig the tubers not bruising the delicate skin. Leave the harvested tubers on top of the soil for a few hours to dry. Cure your sweet potatoes in an 80F, well ventilated room for 10 days. This will help transform the starches into sugars. Store them in a 55F degree room.
Now for this week’s tip, those white, fuzzy caterpillars that are crawling all over plants and buildings are tussock moth larvae. They only cause damage in high numbers and are easily controlled with sprays of Bt.
Next week on the Vermont Garden Journal on Vermont Public Radio, I’ll be talking about a collection submitted to the Vermont Garden Journal on Vermont Public Radio’s Facebook page. For now, I’ll be seeing you in the garden!
Read more about growing sweet potatoes.