Sweet potatoes fall into two basic types, the sweeter varieties popular in the South, known as yams, and the drier, mealier types called Jersey sweets. Botanically, they are all varieties of a New World species of the morning glory family. The true yam, by contrast, is from an unrelated tropical plant that produces huge starchy tubers.

Unlike true potatoes, which are started from whole or sliced tubers, the sweet potato is propagated from the shoots that erupt from the seed tuber once it is coaxed into growth in the spring. The gardener must plant the rootless “slip” right away in the prepared garden bed: Make a hole, stick the shoot in about halfway and space them 18 to 24 inches apart. You must keep the soil wet for a week or two until the slips grow roots. Consider cutting the shoots at soil level, which reduces the risk of a slip carrying a disease in the tuber.

A bed dedicated to sweet potatoes should be sunny, free-draining and sandy, which is why you need to amend the soil. Heavy clay soil just won’t do. Don’t add lime or high nitrogen fertilizers, but feed them with potash. The vines should be watered regularly; uneven moisture causes the potatoes to crack. The vines grow to three feet or more and need some space, along with good soil preparation.

Rodents can be a problem, particularly voles, and if you have rats in your plot, this might not be the crop for you.

Sweet potatoes will keep well into the spring if they are handled and stored properly. Cuts and bruises from digging or rough treatment will cause them to rot. Dig them carefully and never wash them until you are ready to cook with them.

And they must be cured by lying out in a warm room for a week or more. Temperatures must stay above 55 degrees to prevent spoiling — they are not for the traditional cool root cellar.

Curing not only preserves them, it improves the flavor in some varieties. ‘

Old-time sweet potato varieties:

• Hayman white is a flavorful sweet heirloom variety originally from Maryland. Each plant produces a lot of small tubers.

• Puerto Rican, also known as Porto Rico, is the closest in size and color to the robust supermarket varieties, with coppery skin and rose-colored flesh.

• Nancy Hall is a small, white yam type that is considered a poor yielder but has excellent flavor.

• Jersey red is valued for its drier flesh and attractively mealier texture. It is a taste from the past.

• Jersey yellow is a yellow-skinned and -fleshed version with excellent old-time flavor.