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Zones 8-10, 12-15, 18-24, 29-33, H1, H2
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Moderate

Sweet potato

Convolvulaceae
Perennials, Vegetables, Vines

Not a potato, but the thickened root of a trailing tropical vine closely related to morning glory (Ipomoea); the scientific name is Ipomoea batatas (see that entry for ornamental varieties). Most varieties trail several feet, but bush and short vine varieties are also available, making it possible to grow them even in modest-size gardens.

Sweet potatoes are classified by flesh type. One has soft, sugary, yellow-orange flesh (examples are ‘Centennial’, ‘Jewel’, ‘Kona-B’, and bush types ‘Vardaman’ and ‘Vineless Puerto Rico’); the other has firm, dry, whitish flesh (examples are ‘Hoo­le­hua Red’, ‘Waimanalo Red’, ‘Yellow Jersey’). Sweet yellow-orange type is incorrectly sold under the name “yam” in grocery stores.

Needs a long, hot, frost-free growing season; is easiest to grow in Hawaii. Requires well-drained soil (preferably sandy loam) and plenty of room. Start with certified disease-free or disease-resistant slips (rooted cuttings) from a garden center or mail-order nursery. To avoid buildup of disease organisms in the soil, don’t grow sweet potatoes in the same location 2 years in a row.

Plant in late spring, when soil temperature has warmed to 70°F (21°C). (You can plant year-round in Hawaii, but spring-planted crops mature faster.) Before planting, work in a low-nitrogen fertilizer; too much nitrogen produces leafy growth at the expense of roots. Set slips so that only stem tips and leaves are exposed; space 1 ft. apart, in rows 3 ft. apart. To ensure good drainage, mark off rows and ditch between them to form planting ridges. Row covers provide added heat and keep out many pests.

Harvest before the first frost (110 to 120 days after planting for most varieties); if sudden frost kills the tops, harvest immediately. Dig carefully to avoid cutting or bruising roots. Flavor improves in storage (the starch is converted to sugar). Let roots dry in the sun until soil can be brushed off; then cure by storing 10 to 14 days in a warm (about 85°F/29°C), humid place. Store in a cool, dry environment (not below 55°F/13°C).

 

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