Sugar Spud : Call them sweet potatoes or yams, they belong on your table and in your garden

I know. You weren’t raised in the American South or some other place where summers are long and sultry. That’s why sweet potatoes are rarely on your plate.

On the other hand, if you did grow up with sweet potatoes, you’re smiling because you often fill your mouth and belly with one of the world’s most delectable comfort foods. In fact, you rarely eat so-called Irish potatoes. That’s because they’re native to cool, dry, high mountains and just won’t grow in sultry climates. Happily, sweets are native to tropical America, where dessert bananas and coconuts prosper.

From their native habitat, there are all sorts of legends to explain how, when and where sweet potatoes landed. One has it that Henry VIII loved the root, regarding it as an aphrodisiac. And why not, with its satiny texture and gratifying sweetness?

Today, sweet potatoes thrive in warm climates all over the world, and each culture prepares them in its own culinary tradition. In Japan, sweet potato slices are a heavenly addition to tempura. In India, pureed sweets blended into whole wheat poori dough give the puffed, deep-fried breads a deep, nutty taste. In Morocco, sweet potato slices are often added to beef tagine , the famous spicy, slow-cooked stew.

In the Americas, although sweet potatoes are a flavorful part of soups, breads and side dishes, for the most part they’re saved for the end of the meal, in everything from souffles to cakes and pies to candies. Dulce de camote is a melting Latin sweetmeat, sometimes made with brown sugar and cooked to a fudge consistency (a flavor that chocolate has got to envy), sometimes combined with chopped nuts, candied fruits, tequila and rum, ripened several days, then served under a mantle of thick cream.

Today’s chefs--with ingredients from all over the world at their fingertips and a public primed to embrace the new--are making innovative changes. In “The New Southern Cook,” for example, John Martin Taylor notes that a sweet potato is now more often prepared “in ways that accent its distinctive earthiness.”

Taylor, a sweet potato aficionado, adds, “I use them the way the French and Italians use pumpkin and squash.” His favorite recipe in the book is sweet potato slices mixed with grated horseradish and whipping cream and baked until slightly soft.

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There are two forms of these roots. Sometimes they’re labeled yams and sometimes they’re labeled sweet potatoes. What’s the difference?

By tradition, those with moist, very sweet flesh should be called yams. Botanists go nuts over this, because the true yam is a tropical root that grows yards long and has a crisp, slippery texture. Most food historians think the name turned up in the South, where early African Americans called the vegetable by a name that sounded like yam .

When the roots have flesh that’s flaky-dry like a white potato’s and only moderately sweet, they’re called sweet potatoes.

It’s not always the case--there are dozens of cultivars grown around the world with all sorts of variations--but usually tan skin means the root has drier flesh and skin in the red-to-purple range indicates more moist flesh. So the darker, the more moist and the sweeter is a fairly safe rule of thumb.

One of the splendid things about a sweet potato is that it sweetens in the cooking process. Sweets with moist flesh take a little longer to cook than those with dry flesh. While you can cook both sorts of roots any way you cook an Irish potato or winter squash, I prefer to mash a dry-fleshed sort. That way I can add my butter and milk and make the flesh moist.

Sweet potatoes should not be peeled. Their peels, like all others, contain nutrition and flavor. Besides, peeling raw sweet potato causes its flesh to discolor. Knives used on sweets should be stainless steel, because carbon steel also discolors the flesh.

Beauregards and Jewells are sold at the supermarket, and they’re fine eating. But why not grow sweets you’d never otherwise be able to taste? Oklahoma Reds have red skin with rosy flesh that’s moist and sweet.

Best of all, consider one of the most exciting vegetables you’ll ever grow, the white sweet potato. White Crystals have cream-colored skin and white, moist, sweet flesh. There’s no giveaway gold on the plate, but their melting texture and luscious flavor will proclaim them the sweetest sort of potato imaginable.

Sweet potatoes aren’t just gorgeous on the plate and in the mouth. The vines are a marvelous addition to a mixed border. The flowers are trumpets in shades of rose and pink. Leaves can be blue-green or even reddish, and heart-shaped or notched or lobed. Sweet potatoes are perennials grown as annuals, although if you don’t have frost and you don’t harvest the roots, the vines will last for years.

To grow them, take a whole potato and sprout it, then plant the long shoots. Be sure the potatoes from which you start the slips are blemish-free.

One small to medium-size root will give you dozens of slips. Start them about six weeks before you expect to plant them, when the soil is at least 50, preferably 70, degrees.

Cover a whole sweet horizontally in a container with several inches of sand, sawdust or chopped leaves. Water thoroughly and set in a warm, airy place out of direct sunlight. Warm does not mean so hot that the potato cooks! Keep moist until the leafy shoots are six to nine inches long.

Sweet potatoes are tolerant of most soils so long as they’re loose and drain well, but rich sandy loam is best. Soil can also be fairly acid.

Given their simple needs, sweets are easy to grow. I’m appalled when I read in garden books that sweets are space grabbers and take a lot of fussing. Although vines of some cultivars can ramble for 10 feet, the vines of Oklahoma Reds and White Crystal are only about a yard long. Others are bush types, with vines a foot long. You can set such plants in good soil a foot apart in all directions.

The plants are best set on the top of a small hill about eight inches high for maximum warmth and drainage. As for companions, the purple-leaved basil is charming amid sweets.

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Folk wisdom says slips must be planted in the late afternoon. Snap off each shoot at its base on the tuber, then snip off the bottom inch of the shoot, which can harbor unfriendly organisms. Poke a hole in the soil with a pencil and set in the slip up to its leaves. Pat firmly in place and water thoroughly.

Keep the soil moist. Sweets are drought tolerant, but they’ll produce better in moist--not wet or soggy--soil.

While plants are getting started, cultivate the soil to keep it loose; loose soil is essential to sweets. After a couple of weeks, when the vines are thriving, mulch the plants with six inches of organic matter, like spoiled hay or chopped leaves or sawdust mixed with a handful of cottonseed meal. This keeps the soil loose, preserves moisture, nourishes the plants and prevents vines from rooting.

Sweet potato vines, like many others, root when they touch soil, forming new plants. Some should be snipped off and moved or discarded but not too many, because a luxuriant canopy of leaves improves the vigor of the plant.

No space, sun or good soil left in the border? Sweet potatoes can be grown in containers of potting soil at least a foot deep and 15 inches wide. Vines can flow gracefully out of pots or handsomely up sturdy stakes set in the pots.

You can expect each plant to give an average of two pounds of roots.

Optimum growing temperatures for sweets are 70 to 85 degrees. The plants are happiest in a steamy climate, not the semi-arid desert where most of us live. If your summer air is on the cool side, cover the bed with black plastic mulch.

Under the most favorable conditions, you can have sweets in three months, but generally early cultivars require four months to mature and standard cultivars take five months.

As do all root crops, sweets need to be fertilized. Using the amounts on the label recommended for the area, dig in equal parts organic cottonseed meal and kelp meal and a veil of steamed bone meal before planting. That should be enough if the soil is rich.

To harvest the biggest sweets, let the plant grow for as long as you can, but dig them before the ground turns cold. If you won’t have frost and the soil stays warmer than 50 degrees, leave the sweets in the ground and harvest when you’re ready to cook them.

The skin of the sweet potato is very delicate, and roots must be handled from harvest to kitchen with care. Dig with a fork, a foot or two from one side of the plant, going slowly so as not to pierce the roots. Separate the sweets, but don’t wash them until you cook them--the less handling, the less chance of spoilage.

For storage, cure the roots: Dry them on the ground in the sun for a few hours, then pack them in boxes in no more than a double layer (single is best). Place them somewhere toasty, between 80 and 86 degrees, for a week or two, then store in a cold (close to 50 degrees) humid place. Check occasionally and remove any that show signs of spoilage. The roots will keep for several months, actually sweetening in storage.

Another excellent way to preserve the crop is to slice and cook the roots, then dry them in the sun until the pieces are hard, one to two days. Store them in airtight containers in a dark dry place, then cook as you would any dried vegetable or fruit.

Be sure not to eat two or three of the best roots; save them for starting a new crop in spring. Grow each crop of sweets in a different place (called crop rotation and essential for warding off problems).

For the fun of it, save a sweet and stand it on end, set 3 toothpicks evenly around it about two-thirds of the way down, then tuck the root into a jar of water. Place it in a window out of direct sunlight.

It will be slow to start, but then you can watch the vines and roots grow enthusiastically. Change the water occasionally and give the vines (not the jar) some sunshine.

* Sources:

Standard yellow- and orange-fleshed sweets are at the market, but you may find uncommon cultivars at a farmers market. Slips of all cultivars mentioned, to be shipped in spring in bundles of 25 or more, from Fred’s Plant Farm, Box 707, Dresden, TN 38225.