Margaret Lauterbach

Tips for growing sweet potatoes in Idaho

Vining sweet potato plants produce a thick covering of leaves that preserves moist soil and prevents weeds from germinating. The leaves are edible too.
Vining sweet potato plants produce a thick covering of leaves that preserves moist soil and prevents weeds from germinating. The leaves are edible too.

I have some favorite plants in the vegetable garden, and one of the most treasured is the sweet potato. The vining sweet potato plant shades soil, winding around peppers and eggplants, and between rows of carrots, beans, beets and other plants. The vines shade bits of bare soil, preventing weed seeds from landing on soil at times, and other times, preventing their germination. It’s a pretty vine, too, with edible leaves. I’ve not eaten the leaves, and I’d caution against eating too many from one plant because chlorophyll manufactured in the leaves feeds the roots (including the sweet potato tubers).

Sweet potatoes are relatives of morning glory (including the wild morning glory or field bindweed), all members of the Ipomea genus. None of them requires a lot of care, and they thrive in our soil and climate.

Folks used to hesitate about growing sweet potatoes in the north, but that was principally because of the recommended curing of the harvested tubers. That curing demands high temperatures and high humidity, both lacking in our area at autumn harvest time. Some agricultural experts, though, claim the curing really is to heal wounds caused during harvest. Others claim curing extends the storability of tubers, but I haven’t had problems affecting the edibility of the tubers harvested last fall. I usually put harvested sweet potatoes in my greenhouse for a few days, where they experience some hot but dry air, then move them indoors to a spare bedroom. I don’t prepare them for meals for at least a week or 10 days, letting the starch turn to sugar during that time. I don’t wash them after digging, but I do brush off any dried mud.

The leaves and tubers are nutritious, providing protein, niacin, calcium, iron, vitamins A, C, B6 and thiamin, riboflavin, folate, magnesium, phosphorus and manganese. Their fiber is also beneficial to the digestive system. You can eat the leaves raw in salads, or cooked quickly in stir-fry dishes, and microwave bake the tubers. Consider the leaves a hot weather spinach. And in autumn, you have the delicious tubers, packed with nutrition even though low on the glycemic scale.

My late expert gardening friend, Ross Hadfield, started growing his own sweet potato slips (sprouts) in February from sweet potatoes he bought at a grocery store. He set the sweet potatoes at the side of the hearth of his fireplace in which he started a fire each evening. I think it was the proximity to heat that spurred his sweet potatoes to sprout. Mine have sprouted in a cardboard box, in a spare bedroom at room temperature.

Sweet potato slips are succulent, moist and fleshy. Some reports advise cutting long sprouts in half, so that one can plant both halves and start two plants. I’ve not done that, but a mistake I did make was using a portion of the mother sweet potato with the sprout. Squirrels found it and devoured the sweet potato bit, leaving the sprout to die on top of the soil. Instead of using part of the sweet potato, just pull the sprout off the mother potato, and plant that to a depth of about a half inch. Space plantings about 15 inches apart. I plant them down the center of raised beds because they won’t need attention until harvest time.

If you have limited space, you may want instead to grow a variety called Bush Porto Rico, even in a large container. Grow the Bush Porto Rico, not the vining variety. You’ll still get the super healthful and delicious leaves and tubers, but not the weed-suppressing vine.

Sweet potato plants are very tender to frost, so don’t plant slips (sprouts) out before all danger of frost has passed, or be prepared to protect them. They don’t require a lot of water, but I use seeping hose to give about an inch of water per week. My beds have abundant organic matter incorporated in them and a top dressing of compost, so I haven’t had to supplement them with fertilizer.

There are many varieties of sweet potato, but the basic differences are in color and moistness when cooked. Those usually available in our supermarkets are improperly called “yams”, but those sweets that have orange flesh (usually dark red or brown skin) are moist after cooking, whereas the lighter skinned, yellow-fleshed sweet potatoes are mealier after cooking. There are also some dark purple (skin and purple-fleshed) and some white-fleshed sweet potatoes available in our stores. I think the lighter the flesh color, the mealier the sweet potato. I detest those plastic-wrapped sweet potatoes available in some stores. Some even have visible mold under the plastic.

When you grow any sweet potato, the tubers don’t widely disperse like Irish potatoes do, but they tend to grow in a cluster. An old Victory Garden era gardening book advises special care during the month of September, when the yield of tubers doubles every two weeks from the first to the last day of September. If an early frost is forecast, cover your vines so you can wait to dig vines in October, at least.

I like to leave them until the last possible moment, then the best way to harvest is to cut the vines back to where the original plant was started. Starting a spading fork at least 6 inches away from the visible plant crown (and/or sweet potato ends) may minimize damage to tubers. Some of the tubers might be partly exposed to sun, since some grow vertically, but that doesn’t damage them as it does the Irish potatoes that develop solanine, which is toxic to humans. Some gardeners wash soil from newly harvested sweet potato tubers, but other folks recommend just brushing soil from them. I’ve done the latter, and haven’t had mold, or a shrinking or desiccation problem with the tubers.

If you have an area about 15 inches square that you could dig out of an ornamental bed in autumn, plant a sweet potato there and let the vine help suppress weeds. Remember, don’t use fertilizer containing pesticide in that vicinity. Far West will have starts of sweet potatoes, and NEON and Edwards Greenhouse will have slips available in late spring. These gems may become your garden favorites too.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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