A great exercise in garden patience is in learning when to harvest sweet potatoes. Sweet potatoes are a long-season crop and it takes months for the tubers to mature, but the anticipation grows right along with the vines and roots. This popular vegetable is not difficult to grow and a great crop for in-ground gardens, raised beds, and containers. Because sweet potatoes are root tubers that grow entirely underground, you can’t judge their harvest readiness by their color, size, or shape. When to harvest sweet potatoes depends on a number of factors, and I’ll cover those here, along with how to cure and store sweet potatoes, plus a few tips for growing the biggest sweet potatoes.

What are sweet potatoes?

In America, sweet potatoes are thought of as a Thanksgiving holiday-meal staple. Looking at the Thanksgiving table, most of the standard foods are fall-harvested seasonal fare: turkey, cranberries, pumpkin, and sweet potatoes. We plant sweet potatoes in the late spring but have to wait as many as 4 months to dig them up in the fall. Don’t confuse sweet potatoes with yams, however, which are tropical plants. And sweet potatoes are also not related to white potatoes. Each of these crops belongs to different families and has different growth habits and needs.

Why grow sweet potatoes 

For me, a shorter list would cover why not to grow sweet potatoes. There are so many reasons to add sweet potatoes to your plot or your container garden:

• Sweet potatoes have beautiful, sprawling vines that can reach 20 feet. These are lovely garden accents, and there are even strictly ornamental varieties of sweet potato vines that shine in pots and planters.
• The vines and leaves cover the ground and smother weeds. Alternatively, if you grow them vertically and weave the vines along a trellis, they create a great living wall.
• Sweet potatoes are relatively insect-pest- and disease-free.
• They’re great storage crops. By following the harvest, curing, and storage advice here, you can be assured you’ll be eating them for months to come.
• Sweet potatoes are versatile kitchen staples. There is no shortage of sweet or savory dishes for these delicious root vegetables. In many recipes, you can use them as a substitute for white potatoes, winter squash (like butternut or acorn), and pumpkin, as well.
• They’re also filling and nutritious. They’re higher in beta carotene than many other vegetables and provide potassium, fiber, and vitamins A and C.

To learn more about how and when to harvest sweet potatoes, watch this step-by-step video:

How long does it take to grow sweet potatoes? 

Sweet potatoes take 85 to 120 days to mature. The days to maturity for the variety dictates when to harvest sweet potatoes. Varieties with shorter growing periods are best for northern climates. When ordering sweet potato slips or starting your own from tubers, be sure to check the days to maturity for that specific variety and choose one that works for your region.

When to harvest sweet potatoes 

Because they’re a long season crop, when to harvest sweet potatoes usually coincides with the start of needing a sweater and a headlamp for the final dog walk of the evening. Of course, this depends somewhat on when you planted your sweet potato slips and what variety you chose. A good indicator of when to harvest sweet potatoes is that the foliage will begin to turn yellow. Sweet potatoes continue to grow until frost kills the vines, but the leaves start to yellow as temperatures drop. Why? These warm-season plants are sensitive to cold temperatures, so your first frost is a major factor in when to harvest sweet potatoes from your garden. 

While the roots are safe underground during a light frost, the sweet potato plants won’t survive. In a hard frost, the sweet potatoes near the surface of the soil can be damaged. Additionally, when soil temperatures drop to 50 F degrees (10 degrees Celsius) or below, the roots can be damaged. These tubers can be eaten right away, but they won’t keep in storage. Cold, wet soil can cause the sweet potatoes to decay in the ground and become inedible. 

Let’s also not forget that sweet potato greens are edible! When to harvest the greens differs from when to harvest sweet potatoes: Go for the spinach-like leaves and shoots when they’re young and tender. Don’t take too much, because you want the plant to be able to have enough leafy green tissue to photosynthesize and send energy to its growing roots. Over harvesting the leaves can lead to smaller tubers.

How to harvest sweet potatoes from the garden

Now that you know when to harvest sweet potatoes, get your tools ready. You need:

• A garden fork or shovel
• Pruning shears
• A basket or bucket
• Garden gloves

Sweet potatoes look like rugged roots, but they’re surprisingly fragile. Take care in handling them to not damage the skin or cause a nick or crack. Surface damage may heal over during curing, but those sweet potatoes will not keep for as long in storage.

Pick up the end of a vine, and follow the vine back to its source. Use the pruning shears to cut the vines from the roots, leaving a little bit of the stems attached to act as handles. Clear away the rest of the vine. Sink a garden fork or shovel into the ground about 18” away from the root, and loosen the soil. Move in closer, if you must, but be careful not to spear your tubers! Pull up on the stem, and a whole string of sweet potato roots should follow. With your hand, carefully dig around in the soil to feel for additional roots that became separated. The tubers grow in the top 8 to 10 inches of soil. Gently remove soil clumps from the roots, but don’t use water or a harsh brush on them.

The sweet potato stem exudes a milky sap that can leave sticky black spots on your skin. They eventually do wash off, but this is why garden gloves are nice for harvesting sweet potatoes.

How to harvest sweet potatoes growing in pot 

Harvesting sweet potatoes from a pot couldn’t be easier. Follow the guidelines for when to harvest sweet potatoes outlined above. When it’s time, all you have to do is lift the sweet potatoes from the container. A digging fork isn’t necessary. Reach your hands into the potting mix to support the roots as you lift. Gently turn the pot on its side, if you need to loosen the soil. Cut the roots from the vine with pruning shears. Whether you’re harvesting sweet potatoes from the ground or a pot, handle them gently.

Curing the tubers

If you’ve harvested sweet potatoes with significant damage—maybe a vole found your bed or a sweet potato was dropped and split open—go ahead and eat those right away. These may not cure and won’t keep as well in storage, if they do cure. Newly dug sweet potatoes have a less-developed flavor than those that have gone through the curing process. During curing, starches are converted to sugars, making sweet potatoes actually sweet.

The ideal conditions for curing sweet potatoes will allow you to keep these garden gems to eat all winter. To cure, hold the sweet potatoes at:

• 80 to 85 degrees F (27 to 29 degrees Celsius) with 85% to 90% relative humidity for 10 days
• Or 65 to 75 degrees F (18 to 24 degrees Celsius) with 85% to 90% relative humidity for 2 to 3 weeks

Achieving the high humidity can be a challenge. Your best bet may be to place the sweet potatoes in plastic bags in a single layer. Close the bags and cut some slits for aeration. This will keep humidity high but allow excess moisture to escape. Put the bags in a sunny part of your house so they can warm up during the day.

A backyard greenhouse is another option, if you have a way to heat it at night. Keep the curing sweet potatoes out of direct sunlight, in this situation. 

Storing sweet potatoes

Sweet potatoes require different storage and handling than most vegetables. Just as the roots can become damaged in cold soil, they can become damaged in cold storage. A temperature of 55 to 60 degrees F (13 to 16 degrees Celsius) is ideal for maximum storage life. A refrigerator is too cold. You may be able to wrap cured sweet potatoes in newspaper and store them in a cool closet, pantry, or basement.

If your storage conditions are too warm, you may find a sweet potato that sprouts slips. This is still edible; just remove the sprouts. If it happens to be springtime when you find this one, you can grow out the slips to start this year’s crop.

What might have gone wrong 

With root crops, it’s hard to know how things are going until harvest time. Apart from rotting in the ground—which is rare but can happen in cool, wet years—there aren’t a lot of things that can happen to your sweet potatoes that would render them entirely inedible. Two of the biggest sweet potato problems are scurf—a fungal disease—and wild pests, mainly deer and voles.

Scurf causes dark spots across the sweet potato skin. This is a superficial surface condition and doesn’t affect the quality of the sweet potato flesh. In sourcing your sweet potato slips, be sure to find those that are disease-free, as the scurf fungus can remain in soils for several years.

Deer will eat the sweet potato vines, and voles will eat the roots. Both need to be excluded from your growing space. Deer require fencing or repellents. (Read Jessica’s deer-proofing advice here.) Voles can be deterred by keeping the area around your sweet potatoes mowed or tilled. If growing in a raised bed, line the bottom with hardware cloth so they can’t chew through it.

Tips for growing bigger tubers 

Growing the biggest sweet potatoes makes harvesting this crop more fun. The best sweet potatoes start with the best preparation. Here are some tips:

• Don’t plant your slips until you have warm soil: 65 degrees F (18 degrees Celsius) is ideal. Slips are the sweet potato shoots that start a whole new plant. In northern areas, building raised beds and using a black plastic cover will help the soil warm faster. 
• Plant in light, sandy soils, if possible, without too much fertilizer. If you have a heavier clay soil, amended it well with compost to lighten it up. Go easy on the nitrogen unless your soil is deficient; too much nitrogen will encourage foliar growth but not root growth.
• Plant sweet potatoes in an area that receives at least 6 hours of sunlight per day; 8 to 10 hours is better.
• In cooler areas, planting into a black plastic mulch not only warms the soil earlier in the season but can extend the growing season in the fall, making a big difference in the size of your sweet potatoes. In warmer climates, black plastic mulch may make the soil too warm.
• Sweet potatoes can tolerate drought after the first couple of months of growth, but uniform moisture will lead to the best root development. Too much water can cause roots to rot or split.
• Weed your sweet potato patch until the vines start to take over.
• Find more tips for planting the tubers, growing bigger sweet potatoes, and more on in our article on growing sweet potatoes.

Final thoughts

Also keep in mind that even though the real fun in growing sweet potatoes is in digging up and showing off giant roots, you can—and should—eat sweet potato roots of any size. Those very small “fingerling”-sized sweet potatoes are just as tasty.

The patience required in the timing of your sweet-potato harvest will pay off. September—or whenever you break out your evening sweater—will be here soon enough! Then wait just a few more weeks for curing to maximize these roots’ sweetness. All through fall and winter, as you bring sweet potatoes out of storage for holiday meals and everyday meals, you’ll recall what you accomplished in your vegetable garden last year. 

Remember to watch the vines for a change in color and the weather for an impending frost as the season comes to an end. These are signs that sweet-potato-harvest time has arrived. This well-planned harvest will set you up for a successful curing period and then storage. Your sweet potato casserole, stew, quesadillas, and muffins are as good as made.

For more information on growing roots and tubers, be sure to check out these articles:

• When to harvest potatoes
• How long does it take potatoes to grow
• A guide for growing potatoes in raised beds