How to Turn One Sweet Potato Into a Garden Full of Slips

Once the cold weather and frost hits, many gardens close up until spring. But there's one crop you can keep growing right through winter, with no greenhouse and minimal maintenance: the sweet potato.

Overwintering sweet potatoes is simpler than you'd think. Instead of keeping a whole plant alive, you start growing slips indoors. One sweet potato on a sunny windowsill will sprout leafy vines all fall and winter, and each vine becomes its own plant, known as a "slip". By spring, you'll have your free slip starts ready for the garden.

And they're not just a warm-weather crop. Whether your summers are long and hot or short and cool, sweet potatoes can grow in your garden with very little planning.

Garden Tip: Already growing sweet potatoes or ornamental sweet potato vine outside? Snip a few 6-inch vine tips before your first fall frost and root them in water. They overwinter the same way.

The process is simple. Set a sweet potato in a jar of water on a sunny facing windowsill with the bottom third submerged. Root the shoots (slips) that grow, then pot them in small pots of soil, or a grow bag, and keep them in bright light around two to three weeks after your last spring frost. Then plant them outside right in the garden or in a grow bag.

What are sweet potato slips?

Unlike regular potatoes, sweet potatoes aren't grown from chunks of the potato. Gardeners plant slips: the leafy shoots that sprout from a mature sweet potato. Each one grows its own roots and becomes a full plant.

Garden centers and online nurseries sell slips in spring, but they can be pricey and popular varieties sell out early. Growing your own costs the price of one sweet potato, and it's a great windowsill project for kids.

How to start a sweet potato in water

You can start any time over the winter. Aim to have your sweet potato in water about 10 to 12 weeks before your planting date. In warm zones (8 to 10), that means January. In cooler zones (3 to 7), early March is about right.

1. Pick a firm, healthy sweet potato. Organic ones are a good bet, since some grocery store sweet potatoes are treated to slow sprouting.
2. Find the right end. The narrower root end goes down, the wider stem end up.
3. Add toothpicks. Push three or four into the middle so the potato rests on the rim of a jar.
4. Add water. Only the bottom third to half should sit in water. A fully submerged potato rots.
5. Give it light and warmth. A south-facing window is best. On cold nights, pull it back from the glass, since a chilly windowsill can stall sprouting. Change the water every few days.

Be patient. Roots show up first, and leafy shoots can take two to six weeks. The top of the fridge is a handy warm spot to speed things along until shoots appear.

How to take and root sweet potato slips

Once the shoots are about 6 inches long with several leaves, they're ready to become their own plants.

1. Remove the slip. Gently twist it off, or snip it right where it meets the potato.
2. Strip the bottom leaves. Pull the leaves off the lowest couple of inches of stem.
3. Root it in water. Stand the slip in a glass so the bare stem is under water and the leaves stay above.
4. Wait for roots. In about a week or two, white roots will grow along the stem.

Keep the main potato going after you take slips. It will keep producing new shoots for weeks, sometimes months.

Overwintering your slips indoors until spring

Cooler weather brings short days, cold windows and dry furnace air. Your slips can handle all three with a little help, and they make a lovely trailing houseplant in the meantime.

• Pot them up. Once a slip has a few good roots, move it into an grow bag filled of regular potting soil. Soil-grown slips are sturdier than ones left in water for months.
• Chase the light. December and January days are short, so give them your sunniest south-facing window. Pale, stretched vines mean they want more light.
• Keep them away from heat vents and cold drafts. Both dry out or stress the leaves.
• Water when the top of the soil feels dry. Soggy soil leads to root rot.
• Trim long vines. Snip off an unruly vine and root it. Now you've got another slip.

If the original sweet potato turns mushy or smelly, take any remaining shoots and compost it. Your new plants don't need it anymore.

When to plant sweet potato slips by zone

Sweet potatoes love heat and not so much of the cold. Plant them out about two to three weeks after your last spring frost, once nights stay above 55°F.

Northern gardens (zones 3 to 5), like northern Minnesota, North Dakota, Michigan, upstate New York and the Colorado Front Range, have the shortest window. Plant slips in early to mid-June and plan to harvest by early to mid-September.

Middle zones (6 and 7), including Ohio, Pennsylvania, Kansas, Virginia, Tennessee and Oklahoma, can plant from mid to late May. Harvest runs from early to mid-October.

Southern gardens (zone 8), like the Carolinas, Georgia and north and central Texas, can plant from late April to early May and harvest by late October.

Warm climates (zones 9 and 10), including Florida, the Gulf Coast, southern California and Arizona, can plant in April. Since frost isn't usually a worry, harvest about four months after planting.

Please note that dates are approximate. 

How to plant them

1. Harden them off. For about a week, set slips outside a few hours a day, building up to a full day and night.
2. Choose full sun. A sunny, warm spot is where they will do best.
3. Plant deep. Bury each slip up to its top few leaves. Roots form all along the buried stem.
4. Space them about 12 to 18 inches apart. The vines spread.
5. Water well for the first two weeks, then deeply about once a week.

Why sweet potatoes thrive in a raised bed

In northern zones, a short season is the biggest challenge, and warm soil is the secret to beating it. Raised beds warm up faster in spring and drain better than ground-level gardens, giving your plants a quicker start. In the South, that drainage keeps roots from rotting after heavy summer storms.

Loose soil matters too, since sweet potatoes grow bigger and smoother when they're not fighting heavy clay. A Cedar Planters raised garden bed gives you 12 inches of planting depth, and at 30 inches tall, there's no kneeling at harvest. Beds come in lengths from 24 to 72 inches, built from WRCLA-certified Western Red Cedar that's naturally rot- and pest-resistant.

Ready to give your slips a warm home this spring? Shop the Raised Garden collection and have your bed set up before planting day.

Harvesting and curing your sweet potatoes

In most zones, dig them up before your first fall frost, using the harvest timing for your zone above as a guide. In frost-free areas, harvest about four months after planting, once the leaves start to yellow. Cold soil damages the roots, so if a frost warning pops up, dig that day.

Dig gently and wide around each plant. The skins are thin at harvest and bruise easily.

Then comes the step most people skip: curing. Fresh-dug sweet potatoes aren't very sweet yet. Leave them unwashed in a warm spot, like near the furnace room, for a week or two. Then store them around 55 to 60°F. Skip the fridge, cold garage and root cellar, which are all too cold and ruin the texture.

FAQ

Can you grow sweet potatoes in northern states?

Yes. Your harvest may be smaller than in the South, but a fast-maturing variety, warm soil and your sunniest spot make a big difference. Gardeners in zones 3 to 5 grow them every year.

When should I start sweet potato slips?

Start about 10 to 12 weeks before your planting date. That's January in zones 8 to 10 and early March in zones 3 to 7. Starting in fall works too if you want to keep them as houseplants over winter.

Why isn't my sweet potato sprouting?

Give it up to six weeks and a warmer spot, away from cold window glass. If nothing happens, it may have been treated to slow sprouting, so try an organic one.

How many slips should I plant?

Plan on one slip for every 12 to 18 inches of bed length. Each plant usually gives you several sweet potatoes.

Are the leaves edible?

Yes. Young sweet potato leaves are tasty sautéed like spinach. Just don't strip a plant bare, since it needs those leaves to grow its potatoes.