October 4, 2013

By William Woys Weaver

Heirloom Vegetable Gardening by William Woys Weaver is the culmination of some thirty years of first-hand knowledge of growing, tasting and cooking with heirloom vegetables. A staunch supporter of organic gardening techniques, Will Weaver has grown every one of the featured 280 varieties of vegetables, and he walks the novice gardener through the basics of planting, growing and seed saving. Sprinkled throughout the gardening advice are old-fashioned recipes — such as Parsnip Cake, Artichoke Pie and Pepper Wine — that highlight the flavor of these vegetables. The following excerpt on heirloom sweet potato varieties was taken from chapter 34, “Sweet Potatoes.”

To locate mail order companies that carry heirloom sweet potato varieties, use our Custom Seed and Plant Finder.Check out our collection of articles on growing and harvesting heirloom vegetables in Gardening With Heirloom Vegetables.

A Brief History of Heirloom Sweet Potato Varieties

The sweet potato (Jpomoea batatas) is a morning glory that produces roots. It is a tropical plant that thrives in a warm, sunny climate and prefers loose, well-drained soil. Because it requires a long growing season, its culture is concentrated primarily in the South, where virtually hundreds of backyard varieties abound. With careful planning, however, it is possible to grow sweet potatoes in most sections of the United States. Even in Chester County, Pennsylvania, where I live, there are ample references to farmers raising sweet potatoes in the eighteenth century. Philadelphia botanist John Bartram grew both red and white varieties, which he procured from Florida, and in 1766 instructed his son on the West Indian method of planting them: cut the tubers in half and plant the two pieces in the ground flat side down. That system works in the tropics, but in more northerly regions, other cultural methods prevail.

Sweet potatoes are generally classified by their leaf type, although I find this system confusing, since constant crossing between varieties has resulted in large numbers of intermediate leaf shapes that defy categorization. This is further complicated by the fact that in the South many people refer to sweet potatoes as yams, which are botanically unrelated, and categorize certain sweet potatoes with short, fat, stumpy tubers as a “yam type.” Confusion is further compounded by the grocers who sell yams as sweet potatoes because the public thinks that sweet potatoes must be yellow or orange. Most are not. Sweet potatoes come in a wide variety of colors.

One of the leading books on heirloom sweet potatoes is James Fritz’s Sweet Potato Culture, which first appeared in 1886, but was much enlarged in 1902. He lived at Keswick, Virginia, within eyesight of Thomas Jefferson’s Monticello, and was a well-known cultivator of sweet potatoes. His inventory of sweet potato varieties is considered a beginner’s guide for heirloom fanciers, of which there are indeed a great many.

The oldest variety of early American sweet potato thus far documented is the Spanish Potato once grown in tidewater Virginia and Maryland, as well as in colonial Pennsylvania along the Delaware River. The tuber resembled ginger root — often knobby, and sometimes even branching. It was eaten in the winter because it “fattened” in storage, that is, acquired a rich, buttery texture. This variety, which came from Cuba or Jamaica in the 1670s or perhaps even earlier, was popular among all classes of colonists, from slave to planter. In the cabins of the poor and in the kitchens of the rich, pits were dug in the floor near the area of the hearth so that the sweet potatoes could be stored in sand in a warm, dry place. This prevented the tubers from rotting, for sweet potatoes will rot quickly if stored below 50 degrees Fahrenheit. A strain of the Spanish Potato is available on a limited basis through Seed Savers Exchange under the name Spanish Red. It has red skin. There is a subvariety with a more violet-tinged skin, but both produce long, sticklike tubers on trailing vines.

Two later varieties, and probably the ones raised by John Bartram in the
1760s, are the Bermuda Pink and Bermuda White, which are characterized today as “yam” types because of their stumpy shape and ability to grow plump in sandy soil. The Bermuda leaf-type also represents one of the largest groups of sweet potatoes, for many varieties have evolved out of them. The leaf is shown in the woodcut. Both varieties have creamy flesh, but they have different skin textures and colors. The pink has a rose-tinged skin covered with heavy ribs. The white has parchment-colored skin resembling some of the very blond varieties of potato. I raise both sorts in my garden, and their flavor is excellent. They are readily available and can be grown in many regions outside the South.

As a rule, northerners prefer sweet potatoes that are dry and mealy, while southerners prefer varieties that are sugary and sweet. This regional taste
difference is breaking down, since sweet potato culture in the North has declined, especially in the old centers of growing in South Jersey and Delaware. Many of the nineteenth-century varieties that catered to these tastes are now extinct or extremely difficult to obtain. Three nineteenth-century varieties that are dependable and still available are Southern Queen, Nansemond, and Hayman, which I have listed in order of popularity.

Southern Queen matures in 105 days, which is about average for most of the sweet potatoes that can adapt to a wide variety of conditions. It is a vining type that produces long, narrow tubers with white skin and white flesh. The original strain was introduced from South America in 1870.

In Southside Virginia, where this variety originated, Nansemond has been a perennial favorite since 1850, made into sweet potato pies with toasted peanuts and a little peanut flour in the pie crust. There is no better way to pass through the Great Dismal Swamp than with this culinary treat (and maybe a bottle of Virginia Gentleman) packed into one’s survival kit. Nansemond is yellow, but there is also a subvariety that is red, and an improved variety called Hanover, after the Virginia county where it was developed.

Hayman is a white-skinned white sweet potato that was developed on the Eastern Shore of Maryland. In Philadelphia, we always called it the “terrapin potato” or the “crab potato” because it was used so much in making croquettes and stews, and it is so superior to potatoes when cooked with shellfish that it is a great wonder why it is not better known. I fault the Marylanders for not sticking up for their own inventions; when cured in the sun, this sweet potato is not only highly aromatic — perfect for a crab boil — but also fragrant of cinnamon, which is not bad when it comes to making pies.

I raise a few other sweet potatoes of uncertain origin — one called Amish Pink, which does well in Pennsylvania and the Midwest, and two varieties obtained from Wayne Miller of Littlestown, Pennsylvania. These were raised without varietal names by his grandmother Bertie Missouri Miller, a formidable lady who was well known in the Gettysburg area for her sweet potatoes. All of these are vining types.

Grow Sweet Potatoes

Sweet potatoes are generally started from slips created in the spring by planting sweet potatoes held back for seed in a hothouse or hotbed and letting them sprout. The suckers are pulled off and planted once the threat of frost has passed. In the South the suckers are generally planted on ridges, but this is due more to the nature of the soil there and the types of sweet potatoes grown. In the North sweet potatoes thrive better when planted on flat ground, although the ground should be worked deeply and be well manured. I use rotted horse manure — smelly maybe, but worth its weight in gold.

Sweet potato vines will sprawl across the ground and take up a great deal of space, with some vines reaching 16 feet long. It is possible to increase production by covering vines at their joints with a shovelful of soil. These joints will then root and produce tubers. In the South, the vines may blossom. If there is more than one variety in the garden, they will cross, and the seed will produce hybrids. From this seed come the numerous backyard varieties that exist today, as well as the commercial varieties created under more controlled conditions. Sweet potato vines rarely bloom in the North; in fact, I have never seen a sweet potato flower, even though I have raised sweet potatoes for quite a long time. As long as the potatoes are reproduced from the tubers, and not from seed, more than one variety can be grown in the garden at the same time, even in the same bed. It is advisable, however, not to plant varieties together that look alike, as they may become mixed together too easily during harvest.

Late in the fall, when the leaves of the plants begin to yellow — usually late in September — the potatoes are ready to harvest. They should be dug and cured in the sun for a few days to increase their sweetness, then separated, setting aside the best for seed and storing the rest for winter.

How to Store Sweet Potatoes

Storage is a major problem for some gardeners; if conditions are too cold, the tubers will rot. Wayne Miller wraps his potatoes in old newspapers, taking care to eliminate any that are damaged or bruised, and then stores them at 65 degrees F in a specially rigged refrigerator. This system works perfectly.

I store mine in a dry pantry and check them weekly. In reading through an agricultural report from the 1850s, I spotted a letter from an Ohio farmer who wrote that he stored his sweet potatoes in dry sand packed down in boxes in a cellar kitchen. The boxes were set up on scantling (wooden slats) so that they would not draw off dampness from the floor. This idea is very good for market gardeners who are raising sweet potatoes on a large scale, but it may not guarantee seed stock over the winter. Sweet potatoes that begin to soften or discolor can always be salvaged for cooking, but not for next year’s crop.

The French were confronted with this problem in the 1830s; the king of France at that time was fond of sweet potatoes, yet the climate around Paris was not conducive to their culture. Their solution was to grow the sweet potatoes in a hothouse and simply root shoots taken from the vines each spring. Since sweet potatoes are perennial in the tropics, this clever system works perfectly, and I use it myself. My seed potatoes are planted in Styrofoam ice chests, and from these vines I root slips for my spring plantings. By growing the mother plants as perennials, I preserve plant purity and avoid the worry of losing seed stock over the winter. Furthermore, the leaves of sweet potatoes are entirely edible and can be cooked like spinach greens. Therefore, by pruning my vines, I not only have a supply of greens over the winter, I also encourage the vines to branch and produce more rootable shoots.

Find seeds for these heirlooms and more with our Custom Seed and Plant Finder.

Photos and Illustrations Courtesy William Woys Weaver.