let there be sweet potatoes: how to plant them

B ETWEEN A ROW OF CUTTING TULIPS AND ANOTHER OF ALLIUMS, on a mounded “ridge” of soil created for the purpose, the sweet potatoes were tucked in here a week ago. You have to love a seed or plant that comes in the mail complete with recipes: how optimistic, how confidence-inspiring. My box of “slips” included all the details on planting, sure, but also on making sweet-potato fries and sweet-potato pie, and I cannot wait. But there are probably just a few details to consider before I fire up the stove:

Unlike white potatoes, where you plant a “seed potato” whose eyes are starting to sprout, with sweet potatoes you start with bits of vine called slips. Glenn Drowns of Sand Hill Preservation Center in Iowa, who lists more than 100 sweet-potato varieties in his amazing catalog, explains the origin of the word slip:

“A slip is a single plant (with small roots) that is sprouted on the sweet potato root and then slipped off so that you may plant it in the garden to grow a sweet potato plant.”

Each slip doesn’t look like much when it arrives—a piece of vine with some roots and maybe a leaf or two, usually a little pale and worse for the wear after days in transit. But it will quickly rebound if planted promptly according to some basic guidelines (that’s the above-ground bit of one a day or two after planting, above):

The more deep, loose soil you give the plants, the more easily roots (potatoes) will form, and apparently they will also be smoother if not expected to bump into to many obstacles when they grow. Hence the idea of creating a ridge (sort of an elongated hill), but a raised bed would be fine, too, or for that matter any well-cultivated area.

Space the plants 12 inches apart within the row and rows 36 inches apart, because these things take off in wild, vining fashion. I don’t mind; both adjacent rows of cutting bulbs (the tulips, right, and the alliums, left, in the photo above) will soon go dormant, and since I don’t need to dig to plant or harvest the sweets, it works out well; the bulbs won’t be disturbed by this neighbor in between.

Gardeners in the north may want to pre-heat the soil by stretching black plastic over their rows, as in the audio-less video I happened on (below) from Johnny’s Selected Seed, piercing the plastic every 12 inches to insert a slip. I skipped the plastic; my one long recycled piece of it was called into duty elsewhere this year, so we shall see. [Update: I regretted skipping the plastic, as much as I loathe the stuff, because the vines rooted i along their stems and I got more small potatoes than large ones.]

Water each transplant in and firm the soil around it, and that’s about it…except one thing: If your slips arrive as mine did before the weather really settles, you’ll have to have some Reemay or an old sheet ready for protection. These are heat-lovers, not cold-hardy types.

In late summer, check the ridge by just digging in with your hand to see what’s formed, to judge readiness. Digging (as with white potatoes) is best done very carefully, to avoid piercing the roots; again here the ridge comes in handy, as you can basically “dig” by hand.

After digging, potatoes must be dried thoroughly to cure, and then stored at 55 to 60 degrees. With common varieties like ‘Beauregard,’ one that I am growing on my first major sweet-potato adventure, large potatoes up to 2 or more pounds are possible; other varieties vary widely in productivity, shape, size and even skin and flesh color. Just scan the list at Sand Hill to grasp the possibilities.

Want to try your hand at sweet potatoes? Longtime grower and mail-order source the Steele Plant Company in Tennessee is sold out for the season, as is Johnny’s Selected Seeds in Maine, but check in with Sand Hill to see if Glenn Drowns still has some of his “Season Closeout-General Assortment” specials left, the only thing he takes orders from after mid-May, and then ships late June into mid-July. You might get lucky. If not, order as soon as the catalogs arrive in early winter…to guarantee that homemade pie and sweet-potato fries in 2010.