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Planting, Growing, and Harvesting Sweet Potatoes
A few sweet potato plants can produce a generous harvest! This nutritious, sweet-tasting root vegetable is heat-tolerant and pest-resistant. Here is everything you need to know about growing sweet potatoes.
Though commonly grown in the South because they require warm weather, northern regions can have success, too. See our advice on which varieties to choose below.
About Sweet Potatoes
The sweet potato is a tropical plant and is actually a member of the Morning Glory family. Compare a sweet potato vine鈥檚 foliage and flowers to those of morning glory, and you鈥檒l see the family resemblance! Despite their name, they are not related to potatoes, which are in the nightshade family. Another difference between sweet potatoes and 鈥渟tandard鈥 potatoes is that the edible portion of the sweet potato is a tuberous root, not a true tuber (which are technically modified plant stems).
This root vegetable has deep-orange flesh and a coppery skin jacket. Sweet potatoes are commonly served cooked in mashed form or roasted whole. They may also be used as pie filling.
This tropical crop needs at least 4 months of warm weather and warm soil, but they are drought- and heat-tolerant and have few pests or diseases. Although traditionally more of a Southern crop, there are many short-season sweet potato varieties today. They will grow in the North (even parts of Canada!) when grown in sandy soil or raised beds mulched with black plastic to keep the soil warm.
Sweet Potato Slips
Note that sweet potatoes are not grown from seed. Instead, they鈥檙e grown from slips, which are sprouts from existing sweet potatoes. Slips are often available at local garden centers and nurseries, from local farmers (such as farmers鈥 markets), or mail-order companies. Or you can start your own (see below).
Before you order slips, please make sure that you have a long enough growing season to grow sweet potatoes. Most varieties will take about 90 to 120 days to mature. See your frost dates and length of growing season. Also, ensure you time your order with your planting dates in mind!
Planting
Choose a sunny spot with well-draining soil. Sweet potatoes aren鈥檛 too picky, but they do prefer soil on the sandier side. They need plenty of air space in the soil for roots to reach down. Consider growing in raised beds if your soil is clay, rocky, or compacted.
Add compost, perlite, and/or coconut coir to the growing area to build fertile, loamy soil down to 8 to 10 inches. Avoid adding animal manure, including pelleted chicken manure; it can result in spindly and/or stained roots. Also, avoid heavy nitrogen fertilizers, which produce lush leaf growth at the expense of the edible roots!
When to Plant Sweet Potatoes
- Plant slips outdoors, 3 to 4 weeks after your last spring frost or once the soil has warmed to at least 65掳F (18掳C). Nighttime temperatures should be at least 55掳F (13掳C). The trick is to plant them early enough to have time to mature fully but not so early that they get killed by a late spring frost.
- Be sure to protect young sweet potatoes from late frosts or cool nights (lower than 55掳F/13掳C), as they are very tender. Cover them with plastic milk jugs or use row covers, removing the covers during the day.
- If you ordered slips from a mail-order source, unpack them right away. Stick the roots in water for a day or so, and they鈥檒l perk up. Plant them as soon as conditions are right.
Credit: Lex20/Getty Images.
How to Grow Your Own Sweet Potato Slips
You can start your own slips instead of buying them, but it鈥檚 more work. Here鈥檚 how:
- About 8 weeks before your last spring frost date, look for unblemished, smooth, organic sweet potatoes at the store or farmers market. Be sure to ask about the variety and check that it鈥檚 one you want to grow.
- Place the whole sweet potatoes in pots or bins that contain at least 3 inches of light, organic, well-draining soil. Leave an inch or two of space between each sweet potato.
- Lightly cover with a few inches of additional soil. Water now and as needed to keep soil damp but not soggy.
- Maintain the soil and the room at 75掳F to 80掳F in sunlight or under artificial lights. Use a heating mat if necessary; sweet potatoes respond well to warm temperatures.
- Soon, slips (shoots) will emerge from the soil.
- After about 6 to 8 weeks, the slips should be between 6 and 12 inches long, with a number of leaves and roots.
- Remove the slips from the sweet potatoes with roots attached. (If no roots have formed on the slip itself, remove the slip and place it in water; roots should appear in 1 to 2 weeks.)
- If it is still too soon to plant outdoors, stand the slips in potting mix or sand and keep them moist until the right planting time (3 to 4 weeks after the last frost).
- Harden off the slips (before planting outdoors) for 1 to 2 weeks by exposing them to filtered sunlight outdoors during the day.
How to Plant Sweet Potatoes
- Create raised mounds 6 to 8 inches tall and about 12 inches wide.
- Plan 3 feet between mounds so there is enough space for vines to run.
- Plant the slips on a warm, overcast day when the soil temperature has reached 60掳F (15掳C).
- Break off the lower leaves, leaving only the top ones.
- Set the slips deep enough to cover the roots and the stem up to the leaves. Sweet potatoes will form on the nodes.
- Water with a high-phosphorus liquid fertilizer, then water generously for 7 to 10 days to make sure that the plants root well.
Growing
- Side-dress the sweet potato plants 3 to 4 weeks after transplanting with 5-10-10 fertilizer. If you have sandy soil, use more.
- Weed the sweet potato beds regularly, starting 2 weeks after planting.
- Avoid deep digging with a hoe or other tool that disturbs the delicate feeder roots.
- Water regularly, especially during mid-summer. Deep watering in hot, dry periods will help to increase yields.
- Do not prune sweet potato vines; they should be vigorous.
- Late in the season, reduce watering to avoid cracking of the sweet鈥檚 skin鈥攁 problem in storage.
Credit: Getty Images.
Growing Sweet Potatoes in Containers
Bush-type sweet potato plants are ideal for container growers. The vines that they produce are short and compact, not sprawling like typical sweets鈥攂ut the roots are full size, not miniatures.
While slips mature, prepare a large container or tub. (A too-small container can result in small, curly sweets or fewer than hoped for.) A 10-gallon container can support two or three sweet potatoes; a 20-gallon one, four to six. A half-barrel container (20 to 25 gallons) is ideal. Place the container where it will receive full sunlight every day. (It will be heavy to move once filled and planted.)
Sweets like moist but not wet soil; the medium must be well-draining and rich; sweets are also heavy feeders. Provide potting mix amended with compost, sand, bonemeal (for potassium), and wood ash (for potash). Minimize nitrogen or risk producing heavily leafy tops and spindly roots. If you purchase a bush variety, soak the roots in water for a few hours before planting.
Plant slips 3 to 4 weeks after the last spring frost, when the soil has warmed to 65掳F and nighttime temperatures are at least 55掳F. Mulch with black plastic before and during the season, if necessary, to capture or retain heat. Set slips 4 inches deep on a bed of compost, then cover up to their bottom leaves. Water with a high-phosphorus liquid fertilizer (5-10-10) for 7 to 10 days to ensure that the plants root well.
Harvesting
- You can start digging up the roots when they are big enough for a meal.
- Harvest when the leaves and ends of the vines have started turning yellow or about 100 days from planting.
- Loosen the soil around each plant (18 inches around, 4 to 6 inches deep) to avoid injuring the roots. Cut away some of the vines.
- Pull up the plant鈥檚 primary crown and dig the roots by hand. Handle the sweet potatoes carefully, as they bruise easily.
- Shake off any excess dirt; do not wash the roots.
- Complete harvesting by the first fall frost.
How to Cure and Store Sweet Potatoes
- Curing sweet potatoes gives them a sweet taste and also allows a second skin to form over scratches and bruises.
- Handle sweet potatoes carefully; they bruise easily.
- To cure, store roots in a warm place (about 80掳F) at high humidity (about 90%) for 10 to 14 days. A table outside in a shady spot works well. Arrange sweet potatoes so that they are not touching.
- After curing, discard bruised sweet potatoes, then wrap each one in newspaper.
- Carefully pack in a wooden box or basket. Store in a root cellar, basement, or the like with a high humidity at 55掳 to 60掳F.
- The roots should last in storage for about 6 months.
Cooking Notes
Relatively low in calories, sweet potatoes are very nutritious, a top source of beta-carotene, and contain some protein, calcium, iron, vitamins A and C, and other minerals. They can be stored longer than winter squash.
To cook, sweet potatoes are easier than pie (or sweet potato pie!).
- They can be scrubbed, poked with a fork in a few places, and baked at 400掳F for 35 minutes to 1 hour, until they give a bit when you squeeze them in your pot-holder鈥損rotected hand.
- In the microwave, a whole sweet potato baked on high should be ready in 4 to 6 minutes. It may still feel firm when done; let it stand for about 5 minutes to soften.
- Sweet potatoes can also be steamed whole (cleaned and unpeeled) for about 40 minutes or until tender or cooked whole (cleaned and unpeeled) in boiling salted water for about 35 minutes. (Boiling reduces the flavor considerably.)
- Immerse cut raw sweet potatoes in water until you’re ready to cook them; they will darken otherwise.
As a general rule, don’t substitute sweet potatoes for regular potatoes in recipes; the two aren’t related. Sweet potatoes don’t hold together the way potatoes do, and their strong flavor can overwhelm a dish meant for a milder potato taste. Sweet potatoes are also not related to yams. But they make a fine substitute for pumpkin, especially in desserts.
Check out our ten best sweet potato recipes!
Catherine Boeckmann
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1. Yes, you can grow both sweet potatoes and the ornamental sweet potato vine vertically. The vines make an attractive decoration while the tubers are growing in the soil. However, the vines don’t twine or cling, so you need to support them, such as tie the stems to the trellis loosely with strips of pantyhose.
2. Your growing season is about 154 days. (See our Frost Dates page for more: http://www.almanac.com/gardening/frostdates/MI/Marquette). There are some varieties of sweet potatoes that can work within your time frame, especially if you use season extenders and start indoors. The soil needs to be at least 65F before you plant outdoors. Planting slips outdoors would likely be in late May or June (May 11 being your last expected spring frost date).
3. A sweet potato is not a potato but the elongated root of a vine in the morning glory family. Its smooth skin can be white, yellow, brown, red, or purple. White-flesh sweet potatoes aren鈥檛 as sweet as the bright-orange types and have a drier texture. In North America, the orange types are often called yams鈥攁nd there lies the confusion.
A true yam, sometimes called a tropical yam, is a tuber from one of several tropical vines. A yam can be similar in size to a sweet potato or grow more than 8 feet long in the wild. It has rough skin that can be cream, brown, or pinkish. The flesh is white, yellow, pink, or purple and is sweeter and moister than that of a sweet potato.
Can you plant a rooted sweet potato, that was started in a jar of water, or just the slips?
You have grown a slip…plant if for sure!
Good morning - we planted sweet potatoes in our church garden and we're not sure of the variety - but we planted on May 14th - my question is how do we know they are ready to harvest - can you see the potato above ground or do they grow underground like regular potatoes?
Looking forward to hearing from you
Best Regards Robert W. Flowers
Greetings, Robert! Sweet potatoes are roots that grow underground from a vine. Usually, sweet potatoes are ready to harvest when the leaves and ends of the vines have started turning to yellow. See more details above in the harvest section. All the best with your harvest, your Old Farmer’s 蜜桃恋人 editors
I planted my sweet potatoes in may is it safe to say I should harvest them in the fall, maybe November?
The days to maturity for sweet potatoes will vary with variety, and ranges between about 90 days to 140. If you know the variety that you are growing, count out the recommended days from the time you planted for a guideline as to when to harvest. For example, if you planted on May 15, and you had a 120-day variety, you would harvest around the middle of September. Some gardeners harvest early sweet potatoes in late summer, when they are about 1-1/2 to 2 inches long, but others wait until they are of a more mature size, usually harvesting around September/October, when the leaves start to yellow, or there is a light frost, but before there is a killing frost and before soil temperatures drop to 55F and below. It will depend on your climate. For a general guideline for your area, visit the following page and type in your zip code — it will give you a chart with planting and harvesting dates for various crops, including sweet potatoes.
/gardening/planting-calendar
For 6 to 7 years now, I have been cultivating sweet potatoes on the same land, and my output is getting lower. What could cause that?
My sweet potatoes vines are running all over the garden. They are green But the leaves have a few eaten areas on them. Is it okay to spray them with seven spray?
Since this is a crop you will consume, we wouldn’t recommend spraying it with pesticide. Instead, try to identify what is chewing your plants. A number of leaf-eating insects are active at night. Bring a flashlight into the garden after sun down to see what’s out there (check the underside of the foliage). In some cases, you can curb the problem by picking off the predators and dropping them into soapy water.
