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Mysterious no more...the sweet potato.

Mysterious no more . . . the sweet potato

Few vegetables are as tough as sweet potatoes --drought tolerant, easy to grow, and productive, yielding 1 to 4 pounds per plant depending on the plant and weather. They're also rich in vitamins A and C, and make an attractive ground cover.

But for all their attributes, they remain something of a mystery to many home gardeners, and they aren't widely grown. There's some confusion in the terminology, too: for instance, when is a sweet potato a yam, and vice versa?

The vegetable referred to as a yam in this country is actually a sweet potato, but it's a moist-flesh type; "Garnet' and "Jewel' are examples. The ones called sweet potatoes are dry-flesh types, such as "Jersey' and "Okinawan'. The true yam is tropical and is not grown commercially in the United States.

Sweet potatoes grow best in warm inland areas and require about 120 frost-free days to mature. But gardeners in coastal areas and regions with short growing seasons have reported success by covering soil around plants with plastic sheets or using row covers.

To grow them yourself, you can buy rooted cuttings by mail (see list of sources on page 194) or grow your own cuttings from store-bought potatoes (these are sometimes treated to prevent sprouting; if you get no results in a couple of weeks, buy by mail-order).

Starting your own slips or cuttings

To grow your own, start them about eight weeks before the last chance of frost--this month in mild-winter climates. Each potato will produce 10 or more shoots.

You have several ways to grow transplants. Root whole potatoes in water: poke three toothpicks into the sides at midsection and suspend in a jar of water that covers the bottom tip (the scar end should point up). Or in soil indoors: place them on their sides in a container and cover partway or entirely with soil or sand (see photographs at left); be sure to provide good drainage. Or outdoors, in a warm climate: bury them in sandy soil in a protected area and cover with plastic. For the latter two methods, keep the growing medium moist but not wet.

If you start them indoors, set containers in a warm place to root, such as on a furnace or hot-water heater. When sprouts appear, move to a sunny window or under a grow light. Shoots develop fastes if potatoes are kept between 75| and 85|.

When soil-started shoots are about 8 inches long, carefully pull them off with roots attached. Snip 8-inch cuttings from potatoes started in water. Leave part of the shoot on the potato so it will continue to grow; you can make additional cuttings later for future plantings. In warm areas, sweet potatoes can be planted over a two-to three-month period.

Planting: not much to it

To produce well-formed roots, sweet potatoes need loose, fast-draining soil. Before planting, cultivate the soil about a foot deep and work in plenty of organic matter. Mix in 5 pounds of 5-10-10 fertilizer per 100 feet of row and form 8- to 10-inch raised rows; flatten the tops for planting.

Set plants about 14 inches apart in rows 2 1/2 to 4 feet apart. Plant deeply so three-fourths of the stem is covered (unrooted cuttings will root in a few days). If the area is very weedy, just after transplanting spray the ground with a pre-emergent herbicide, such as dacthal, to control germinating weeds, or cultivate the soil as weeds appear. The potato vines will eventually shade out most weeds.

Care and harvest: let vines sprawl

Once they're planted, sweet potatoes need little care. Keep the soil moist until plants are established, then water deeply about once a week--don't overwater or potatoes will be long and stringly. Plants need less water as vines fill in and leaves shade soil.

Allow vines to sprawl in the garden (each plant spreads 3 to 4 feet). Do not prune back growing tips or root formation may be inhibited. In areas where nematodes are troublesome, fumigate before planting or leave the area bare and weed-free for a year before planting. Reduce water in August; heavy watering late in the season may cause sweet potatoes to crack.

Starting in September, periodically dig down by one plant and check tuber size. When roots enlarge, you can harvest them for immediate use. Sweet potatoes increase in sugar content as they're stored; freshly dug potatoes aren't as sweet.

Finish harvesting before the first killing frost. Dig with a spading fork or shovel (it may be easier to cut off the vines first). To find the potatoes, follow an umbilicalcord-like root from the main plant.

Handle potatoes carefully; they won't store long if they're cut or bruised. Let them dry in the sun for a few hours so the soil brushes off easily. To heal wounds, cure in a warm, preferably humid, spot for 7 to 10 days. Properly cured, roots can be stored for about four months. Store in crates or baskets in a cool place; temperatures below 55| can cause them to rot.

If you don't have a suitable place, you can cook them and store in the freezer. Bake on a rimmed baking sheet in a 400| oven until soft when pressed (about 45 to 50 minutes), wrap whole potato in plastic, and freeze; or peel, steam until soft, mash, and freeze puree in airtight containers.

Where to buy cuttings

Hundreds of varieties of sweet potatoes exist, but few are readily available. Exotica Seed Company offers several unusual varieties, including "Okinawan', "Mexican Purple', and "Hawaiian Red'. Otherwise, try the old standbys. "Jewel' is one of the earliest; "Garnet' is very sweet, with orange flesh and red skin.

Most growers in the Southeast and Midwest can't ship cuttings into California and Arizona. These sources can ship anywhere in the West.

Photo: Set cutting of sweet potato deeply in hole. Three-fourths of stem should be covered

Photo: To harvest mature potatoes, hunt through foliage for crowns; dig into the side of the raised bed and follow an umbilical-cord-like root to potato

Photo: Two potatoes rooted in water: one with tall shoots ready for cutting was started on a hot-water heater and moved to a sunny window after sprouting; one on far left, started in a window, grew more slowly. Another way to sprout (right): partly bury potato in soil or sand and keep moist

Photo: This payoff is a 1-pound "Okinawan' sweet potato

Photo: Proud gardener shows off 2-pound "Mexican Purple' prize
COPYRIGHT 1986 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Publication:Sunset
Date:Feb 1, 1986
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