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GROW YOUR OWN SWEET POTATO SLIPS: With some deliberate planning, you can start hearty new sweet potato slips from tubers saved from last year's harvest.

Unlike many vegetables, sweet potato plants aren't started from seed or from replanted tubers, but are grown from "slips," which are pieces of stem with a few leaves that've been grown from a mother tuber. We used to buy bare-root slips for our garden, believing that growing our own would be very tricky, but we eventually attempted it anyway. While we had some initial problems--and I can warn you about those--we now have a system that results in a number of sizable sweet potatoes every year.

Homegrown Advantages

Through trial and error, we've found several advantages of homegrown slips over purchased ones. We really appreciate the convenience of not needing to order the slips months ahead of time and hope for good weather on the ship date. There is, of course, also the added benefit of self-reliance, which is a bonus for any farm.

If you grow your own sweet potato slips, you'll have the option to delay planting them, allowing you to put your crop in the ground in stages rather than all at once. If you purchase slips, on the other hand, you'll have to jump-to when they arrive and get them all in the garden promptly.

With purchased slips, a certain amount of drooping (transplant shock) is normal. However, homegrown slips will get off to a strong start--a particular advantage for these 90- to 120-day plants in regions that experience shorter growing seasons.

Selecting for Slips

The ideal time to set aside sweet potatoes for slip production is at harvest, when you can choose from the highest-yielding plants. However, if you didn't select at harvest, you can still grow your own slips by retrieving some from your stored sweet potatoes. Select small or medium-sized tubers (1 1/2 inches in diameter) of typical appearance (no rattails). Don't use any tubers that show signs of disease.

If you don't have your own sweet potatoes, buy some from a local grower so you'll get a cultivar that does well in your area. If you're in a cold region with a short summer, choose a fast-maturing type.

I took several wrong turns when I first learned to grow slips, but you don't have to repeat my mistakes! My first big error was to follow growing directions written for farms much farther south. I tried growing slips in mid-January in central Virginia, and had a dismal fight against nature.

I set up a soil-warming cable in a cinder-block-enclosed bed on the concrete floor of our greenhouse. This is how I discovered that most soil-warming cables have thermostats set to switch off the heat at 70 degrees Fahrenheit. That meant I couldn't get the soil warm enough for sweet potatoes.

How to Actually Sprout Sweet Potatoes

* TIMING. Figure out your ideal planting date, and work backward to find your starting date. Planting out usually occurs about two weeks after the last frost. You'll need settled, warm weather. At my location in Virginia, we wait until soil temperature reaches at least 65 degrees at 4 inches deep for four consecutive days. Don't rush into planting too early, or you'll get lower yields.

We plant on May 10, between pepper, okra, and watermelon transplanting dates. It takes 7 to 8 weeks to grow the slips using our method, and the tubers produce more slips if conditioned for two weeks (or even four) before you start to grow slips. So start 10 to 12 weeks before your planting date. For us, that's March 4.

* OPTIONAL TESTING. First, test the roots in a bucket of water--the ones that float are said to yield more and produce better-flavored tubers.

Second, test for viral streaking (color breaks or chimeras). Discard tubers with pale spots or streaks wider than a pencil lead. Cut across the distal end of each tuber (that's the stringy root end, opposite the end that was attached to the plant stem). All the slips will grow from the stem end, so don't cut there! If you can't tell the difference between the ends, ignore this step.

Propagate your own slips for just two or three years to minimize the proliferation of pathogens (disease-causing agents) in your stock.

* CONDITIONING. Conditioning can double or triple the number of slips the tuber will produce in a timely manner. Put the tubers you've selected for growing slips into flats or crates, without soil, in a warm, moist, light place for 2 to 4 weeks. Ideal conditions are 75 to 85 degrees with 95 percent humidity. The cut surfaces will heal during conditioning.

* SPROUTING. The best environment for sprouting slips is similar to that for conditioning tubers after harvest, so you can likely use the same location. You'll need 12 inches of headroom.

Plant the selected tubers flat, almost touching, in free-draining potting compost in flats or crates. The tubers don't need to be fully covered with soil. Water them, and keep the compost damp. If your planting medium is without nutrients, feed the tubers occasionally with some kind of liquid feed.

* CUTTING SLIPS. Check the tubers daily. After 5 to 7 days, they'll begin to produce slips. When the slips are 6 to 12 inches tall with 4 to 6 leaves apiece, cut them from the tubers.

Some people twist the slips from the tubers, but this can transfer diseases, so I recommend cutting.

After cutting, bundle the slips with rubber bands and set them in water. The slips will grow more side roots if they're in water for several days. Once a week, plant the oldest, most vigorous slips with the best root structure into 4-inch-deep wooden flats filled with compost. Place the flats in good light in a frost-free location, and provide them with sufficient water.

Planted in the flats, the slips will become sturdy. Ten days before planting, start to harden off the slips.

* PLANTING. If you wish to grow large sweet potatoes, plant the slips vertically in your garden. For average-sized roots but larger total yields, plant the slips horizontally 2 to 3 inches deep. Place 3 to 5 leaf nodes underground and only the tips aboveground; this will give the plants a second chance if frost strikes.

If, on the other hand, you're planting in hot, dry weather, you should water the soil first, and keep the roots enclosed in damp compost as you plant. Sweet potatoes are often hilled to minimize flood damage. Hills can be made before planting. In colder areas, black plastic mulch can be used to warm the preformed ridges for about three weeks before you plant, and may increase both the rate of growth and the yield.

We used to plant slips on the flat in bare soil with overhead irrigation, but we sometimes had to battle weeds with this method. We now use drip tape for irrigation and see fewer weeds. After one wet year, we tried ridging before planting to reduce flood losses. It was difficult to keep the drip tape on the ridges, though, so we planted on alternate sides of the tape; these alternating plantings helped prevent the tape from sliding off the ridges.

Nowadays, we use ridges, drip tape, and biodegradable plastic mulch (even fewer weeds!) to get our sweet potato slips growing. We run the drip tape while planting, and then nudge it to where we want it relative to the plants.

By Pom Dawling

Pam Dawling worts in the gardens at Twin Oaks Community in central Virginia. Apart from presenting workshops at Mother Earth News Fairs, Pam also writes for Growing for Market magazine and is the author of Sustainable Market Farming.

Tips for Careful Cutting

To safely tease rooted slips from tubers without transferring diseases, use a simple pocketknife. You'll want the knife to be sharp so that it separates plant tissue with minimal tearing and cellular damage. Work the knife through a series of sharpening stones with increasingly fine grit ratings to at least 600 grit. Once you've worked the knife to a wire-edge condition, give it a couple licks on a leather strop.

Next, to minimize the spread of diseases among your slips, surface-sterilize your blade with a brief dunk in rubbing alcohol (let it air-dry), and keep the slips from individual tubers separated, if possible. Wiping the blade and re-sanitizing it in rubbing alcohol between cuttings can slow the spread of pathogens that will, over generations, diminish the health and yield of your sweet potato patches.

Finally, when you've finished cutting slips, wash your pocketknife in warm soapy water, dry it thoroughly (a hair dryer or compressed air can speed the process), and lightly oil the pivot joint and any metal surfaces, including the blade, before returning it to your pocket or storing it.

Gritty's Tips

When you grow your own slips, you'll have to plan how many slips you'd like to have on hand for an adequate crop the following season (plus some spares to replace casualties). To help you calculate how many pounds (or tons) of sweet potatoes you want to grow, here are some numbers to keep in mind:

* One plant will produce 4 to 10 roots, each weighing 3 to 17 ounces.

* Yield range is 2 1/2 to 7 pounds per plant, or 276 to 805 pounds per 1,000 square feet.

* Plan for at least 6 to 18 inches of space between each plant in a row. Wider spacing yields larger tubers.

* Sweet potato vines become rampant, so space rows 32 to 48 inches apart.

Calculate how many slips you'll need based on these statistics, and add 5 to 10 percent to that number. If you plan to do the two optional tests (explained at right), include an extra 10 percent.

When you harvest your sweet potato crop, you should save at least one tuber for every 10 slips you want for the following season. Each tuber will produce 10 to 30 slips. Size doesn't affect slip production, so there's no advantage to selecting jumbo potatoes.

When you grow your own sweet potato slips, you have the option to delay planting them, allowing you to put your crop in the ground in stages rather than all at once.
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Author:Dawling, Pom
Publication:Grit
Geographic Code:1USA
Date:Mar 1, 2019
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