Imagine harvesting sweet potatoes in Dutchess County, N.Y. Many Farm & Home Center visitors were surprised to see a cluster of dark red sweet potatoes “hanging” in the soil on Open Gardens Day 8/29/2008. I had pushed aside the luxuriant vines and dug a hole at the side of the sweet potato bed. A few minutes of work exposed the potatoes, which grow straight down.
The sweet potato plant, Ipomoea batatus is native to tropical regions of South America. It thrives in long hot summers but a few varieties can be grown in the north because they mature in only 90-100 days. The variety I grow, Georgia Jets, produces a heavy yield of sweet, red skinned, orange fleshed potatoes.
Sweet potatoes are grown from “slips”: sprouts removed from the sweet potato and rooted. We ordered our slips through a seed catalog. Vendors ship the slips at the correct time of planting in your zip code, so orders for Dutchess County ship in late May for planting in warm soil after all danger of frost is past. Unfortunately the order often languishes in the Post Office over the Memorial Day Weekend – a bad situation for the slips.
After planting, sweet potato slips eventually grow into 4-6′ long vines with flowers that show their relation to morning glories. They can root and produce potatoes along the vine. I’ve found nicely sized tubers up to 2′ away from the original planting.
Sweet potatoes vines will not survive a frost (or deer). Japanese beetles also nibble the foliage. The most common problem with sweet potato tubers is splitting when they get very large, or from uneven moisture. The split potatoes usually heal, and can be stored after curing, although they should be eaten first.
The sweet potato tubers must be dug immediately after frost, but they can be dug any time after they have sized up – as early as late August. The Perdue University Cooperative Extension Service says that “Sweet potatoes should be cured before storing to heal wounds and improve flavor. It is during the curing process that starch is converted to sugar.” Curing is definitely needed for the best flavor: I cooked and served a freshly dug sweet potato this week and the flavor was flat and lacking natural sweetness.
“Cure sweet potatoes by holding them for about 10 days at 80-85°F and high relative humidity (85-90%).” These conditions are very difficult to find in D.C., N.Y. in October, but Perdue says that you can compensate. “If the curing area’s temperature is between 65-75°F, the curing period should last 2-3 weeks.” Just be sure to maintain the required humidity. In the past I’ve cured my potatoes by piling them all together in a big bowl and leaving them on a kitchen counter for a few weeks. Then I laid them on a shelf in my unheated basement, which provides the perfect storage temperature. That worked quite well: the potatoes were still good in March!
This article was first published in the Oct. 2008 issue of Dutchess Dirt. Since then I’ve learned a few more things about curing sweet potatoes.
I tried curing my sweet potatoes in a plastic storage box with the lid in place. That kept the humidity too high; so high that moisture condensed on the lid. Many of the sweet potatoes started sprouting. Luckily I discovered the sprouts while they were still tiny, and moved the sweet potatoes to my basement storage area immediately. The sprouts stopped growing and stayed the same size all winter. When I started my slips the next spring, I chose potatoes with sprouts to root. With roots and warmth the sprouts resumed growing and produced slips quickly.
This year I used a loose dish towel to cover my bowls and plastic bins of curing sweet potatoes. That seems to be working quite well. The humidity is higher than ambient, but not so high it condenses of the sides of the containers.