when-to-harvest-sweet-potatoes

When to Harvest Sweet Potatoes

Sweet potatoes are a classic southern food, used in pies and casseroles, especially around the holidays. They are also used in tempura and dehydrated to make snacks. You can grow them easily in warm climates, and with a little more effort, in colder climates as well. Proper harvest techniques increase quality and storage life.

Are Sweet Potatoes and Yams Different?

Although the names are often used interchangeably, calling sweet potatoes yams is a misnomer. The two are tropical, perennial vines with edible tubers, but that’s the only point of resemblance. True yams are members of a different family. The flesh is typically white and has a dry, starchy texture. Sweet potatoes, as the name implies, are also much sweeter in taste.

What’s the Best Way to Grow Sweet Potatoes?

Sweet potatoes will tolerate relatively poor soil, although they produce better with fertile soil. A sandy loam with good drainage that is slightly on the acid side is a good choice. They should be watered well when growing for better tuber production, texture and taste. However, they don’t tolerate wet soil. The vines will scramble over the ground and don’t need a trellis.

Do Growing Methods Affect Harvest?

Although sweet potatoes have a reputation for growing a decent crop even in poor soil, you’ll get more and larger tubers if you provide them with plenty of humus in the form of compost, well-rotted leaves or aged manure. Shorting them on water also has a negative effect on tuber production. If not grown in full sun, you may have smaller tubers and it will take longer for tubers to develop.

Can You Harvest Sweet Potatoes in Winter?

If you garden in a desert area, you might be able to grow sweet potatoes all year-round. In these areas, you might harvest in winter. Native to tropical climates, they will continue to grow and tubers will become larger as long as the soil remains warm. Make sure you give them adequate nutrients by amending the soil with plenty of humus and water them well.

What Are Some Good Varieties?

Although there are more than 6,500 sweet potato varieties world-wide, your selection will probably be more limited. They come in multiple colors and some are heirlooms. These are usually available:

  • All Gold
  • Apache
  • Beauregard
  • Excel
  • Georgia Jet
  • Jewel
  • Porto Rico
  • White Queen
  • Yellow Jewel.

Do Sweet Potatoes Have Maturity Dates?

Maturity for sweet potatoes is calculated from the time you plant slips until tubers are mature. These plants do best in long-season areas unless you practice season extension techniques. Here are some examples:

  • Beauregard – 90 days
  • Vardaman – 95 days
  • Georgia Jet – 100 days
  • Copper Jewel – 110-120 days
  • Golden Kumara – 120 days or more.

Can I Harvest Leaves?

In addition to the tasty tubers, sweet potatoes produce edible leaves. You can harvest your vines in the garden at any time – just pick the young and tender leaves. You can also grown them in water on a sunny windowsill in winter for greens only – not tubers. They can be used as you would any slightly bitter green. They should be cooked and can then be dressed or served with a cream sauce.

Can I Harvest “New” Sweet Potatoes?

Irish potatoes can be harvested as soon as the tubers are about the size of a hen’s egg for new potatoes. They won’t keep well, but are considered a treat. Sweet potatoes don’t go through a similar stage. You can’t harvest them until the tubers have attained the minimum mature size, which usually occurs about three to four months after you plant slips.

How Do I Know They’re Ready?

The projected maturity date is only an approximate. The first time you grow sweet potatoes, start checking them at least two weeks before they “should” be mature. Gently dig down and see if the tubers have attained some size. If not, check again at two week intervals. The tubers will keep bulking up if the weather stays warm. For future crops, use your findings to estimate actual maturity in your garden.

What’s the Best Tool For Harvesting?

Your soil condition makes a difference when considering harvesting tools. Heavy clay soils are more likely to require a pointed-end shovel. Loose friable soils can be harvested with a three- or four-tine potato fork. If properly used, the potato fork is less likely to cause damage to tubers. In a small garden with good soil, a trowel will also work.

What’s the Best Harvest Method?

Tubers can form a foot or more away from the center of the plant. Dig too close and you risk damage that can result in spoiled sweet potatoes. It’s best to start about 18 inches away from the center. Dig a trench around the plant. Pull up the vine. Slide your shovel or fork vertically into the trench and lever up the tubers. Be sure to dig at least 18 inches deep as well.

Why Should I Cure After Harvest?

When first harvested, sweet potatoes haven’t attained maximum flavor or the best texture. They need about a week to 10 days of curing. Curing also helps toughen skins to protect the flesh. Dry in full sun for a few hours, then place them in boxes lined with newspaper and move to a warm, well-ventilated room. The ideal curing room will be 85 to 90°F (25 to 32°C), with a humidity of around 85 percent.

Can I Cure Sweet Potatoes Outside?

If you can be sure of a period of dry weather, sweet potatoes can be cured outside. Shake or brush off excess soil – don’t wash, as it may encourage rot. Lay the sweet potatoes in a single layer on a table or other flat surface in a shaded area with good air circulation. If the weather is humid, turn the potatoes over once a day to ensure even curing.

Can I Leave Sweet Potatoes in the Ground?

As long as the weather remains warm, sweet potatoes will keep right on growing and the tubers will continue to increase in size. Once the vines begin to turn yellow, your sweet potatoes are generally about ready to harvest. Even though the tubers might seem insulated underground, cold soil and frost can start the decay process in your tubers, so don’t leave the harvest too late.

Can I Harvest Sweet Potatoes in a Cold Climate?

Most gardeners in warmer climates, like USDA Zones 8 and 9, usually try to time the harvest for September or October. In colder areas – some gardeners in Canada have managed to grow sweet potatoes – you’ll need to use season extending techniques in spring for an adequate growth period. Harvest the entire crop at least two weeks prior to the first expected frost.

Can I Harvest Sweet Potatoes in Containers?

Sweet potatoes take considerable room to form their tubers. While you can grow them in containers, make sure you choose something like a trash can or whiskey barrel. When it’s time to harvest, tip the container on its side. Use a trowel or gloved hands to remove soil until you can uncover the tubers. As you empty the barrel, keeping tipping to let all the soil fall out.

Does Harvest Time Affect Keeping Quality?

The longer you can leave your sweet potatoes in the ground, the better the flavor will be. As the weather cools, the sweet potatoes will become increasingly sweet. However, these plants and tubers are frost-sensitive. Leave them until the ground freezes or even gets fairly cold and the tubers are much more likely to rot. Harvesting too early also tends to mean a shorter storage life.

Are Sweet Potatoes Fragile?

Sweet potatoes bruise easily, and once bruised, they are prone to rot. Handle them gently during harvest and when putting them in storage. As you dig them, set aside any that have obvious damage for the compost heap or to feed animals like chickens. Don’t stack them too high, as you may damage them while trying to remove individual tubers.

How Should I Store Sweet Potatoes?

Commercial growers and distributors store sweet potatoes in cool, temperature controlled areas with high humidity and good ventilation. In the home, a basement or root cellar offer similar conditions. It’s best to store in boxes only two or three layers deep, with newspaper between layers. Check at least weekly to make sure nothing has developed rot. Don’t store them in the refrigerator – it will affect taste and texture.