When harvest sweet potatoes?

Information About How To Harvest Sweet Potatoes

So you’ve decided to grow some sweet potatoes in the garden and now you need information about when and how to harvest sweet potatoes once they’ve matured. Read on to learn more.

When to Harvest Sweet Potatoes

When to harvest sweet potatoes depends largely on the seasonal growing. If the growing season has been good with adequate water and sunshine, harvesting sweet potatoes should begin about 100-110 days after planting depending on the variety. A good rule of thumb is to watch for the first signs of yellowing leaves. Usually this occurs in late September or early October before the first frost.

Many people think frost won’t affect your harvest. Sweet potatoes are well insulated underground, after all. The truth is once those vines blacken with frost bite, the answer to when to dig sweet potatoes becomes — Right Now! If you can’t harvest sweet potatoes right away, cut those dead vines off at the ground so the decay doesn’t pass to the tubers below. This will buy you a few more days for harvesting sweet potatoes. Remember, these tender roots freeze at 30 F. (-1 C.) and can be injured at 45 F. (7 C.).

When deciding when to harvest sweet potatoes,

choose a cloudy day if possible. The thin skins of the newly dug potatoes are susceptible to sunscald. This can open the way for infection to enter the tubers and cause damage during storage. If you must harvest sweet potatoes on a sunny day, move the roots to a shaded spot as quickly as possible or cover them with a tarp.

How to Harvest Sweet Potatoes

How to harvest sweet potatoes is every bit as important as when to harvest. Sweet potatoes have delicate skin that is easily bruised or broken. Be sure you sink your garden fork far enough out from the plants to avoid striking the tender roots. Don’t toss the freed potatoes into your carrying container. Place them carefully.

A potato that has been damaged by cuts and bruises will leak a milky juice over the injury. Some people believe this juice seals the injury. It doesn’t. Minor scrapes will heal during the drying process, but the best practice when harvesting sweet potatoes is to set deeply cut roots aside to be eaten first.

Washing the newly dug roots is another common mistake made by many home gardeners when harvesting sweet potatoes. Newly dug roots should be handled as little as possible and moisture should never be added.

What to Do After Harvesting Sweet Potatoes

When we talk about how to harvest sweet potatoes, it’s important to note that it’s more than just knowing when to dig. Sweet potatoes must be cured after harvest and before they are stored.

After digging, allow the roots to dry for two to three hours. Don’t leave them out overnight where cooler temperatures and moisture can damage them. Once the surface is dry, move them to a warm, dry, well ventilated place for 10-14 days. This will not only allow the skins to toughen, but will increase the sugar content. You’ll notice the color change to a deeper orange after several days.

When your potatoes are thoroughly cured, pack them carefully in boxes or baskets and store in a cool, dry, darkened place for the winter. Properly cured sweet potatoes can be stored for six to 10 months.

Knowing how to harvest sweet potatoes properly can increase your storable yield as well as the pleasure derived from enjoying your harvest all winter long.

What are the next steps after digging sweet potatoes? How do I cure the spuds I have just dug? Due to a wetter-than-usual summer, the tubers are unusually large. I would like to ensure that I don’t lose them to decay.

I’ve just finished harvesting sweet potatoes in my own garden. Like you, this year’s harvest has yielded some of the biggest sweet potatoes ever.

Sweet potato varieties are ready to harvest 95 to 120 days after planting in the garden. When the leaves turn slightly yellow they are usually ready to harvest. Because they have thin skins sweet potatoes are easily damaged during harvest so extra care should be taken. Some people even go so far as to wear cotton gloves when harvesting as to not harm the potatoes. Cutting the vines 2 or 3 days before you plan to dig will toughen up the skins.

After harvest, the sweet potatoes should be cured. This involves placing the potatoes in a warm (85 degrees) humid (90 percent) environment for about 4 to 6 days to increase sugar content, heal nicks and bruises incurred during harvest, and increase flesh color.

Once cured, store your sweet potatoes in dry boxes or bins in a room that’s humid and 55 to 60 degrees F. The ideal place to store sweet potatoes is in a root cellar or cool pantry. Do not store them in the refrigerator because low temperatures will cause the sugars to turn to starch.
They can be stored for 6 to 10 months under good conditions.

In the garden, on a trellis, or in a container, sweet potatoes are a beautiful plant. The delicious tubers in the fall just come as an added bonus to the lovely foliage and flowers.

Sweet potatoes grow well in a sunny vegetable garden, but you can also grow them in other parts of your home landscape. Try them as a temporary groundcover or a trailing houseplant. In a patio planter, a sweet potato vine will form a beautiful foliage plant that you can harvest roots from in the fall.

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This warm-weather crop grows worldwide, from tropical regions to temperate climates. The flesh is classified as either moist or dry. Moist, deep orange types (sometimes called yams) are more popular with home gardeners, especially the varieties Centennial and Georgia Jet.

Sweet potatoes are also remarkably nutritious and versatile; each fleshy root is rich in vitamins A and C, along with many important minerals. Use them raw, boiled, or baked, in soups, casseroles, desserts, breads, or stir-fries — and don’t forget to try some homemade sweet potato fries!

Planting

kazoka30/getty

Sweet potatoes will grow in poor soil, but deformed roots may develop in heavy clay or long and stringy in sandy dirt. To create the perfect environment, create long, wide, 10-inch-high ridges spaced 3½ feet apart. (A 10-foot row will produce 8 to 10 pounds of potatoes.)

Work in plenty of compost, avoiding nitrogen-rich fertilizers that produce lush vines and stunted tubes. In the North, cover the raised rows with black plastic to keep the soil warm and promote strong growth.

It’s best to plant root sprouts, called slips, available from nurseries and mail-order suppliers. (Store-bought sweet potatoes are often waxed to prevent sprouting). Save a few roots from your crop for planting next year.

About six weeks before it’s time to plant sweet potatoes outdoors in your area, place the roots in a box of moist sand, sawdust, or chopped leaves in a warm spot (75 to 80 degrees). Shoots will sprout, and when they reach 6 to 9 inches long, cut them off the root. Remove and dispose of the bottom inch from each slip, as that portion sometimes harbors disease organisms.

Sweet potatoes mature in 90 to 170 days and they’re extremely frost sensitive. Plant in full sun three to four weeks after the last frost when the soil has warmed. Make holes 6 inches deep and 12 inches apart. Bury slips up to the top leaves, press the soil down gently but firmly, and water well.

Growing

Logan Mock-Bunting/getty

If you’re not using black plastic, mulch the vines two weeks after planting to smother weeds, conserve moisture, and keep the soil loose for root development. Occasionally lift longer vines to keep them from rooting at the joints, or they will put their energy into forming many undersized tubers at each rooted area rather than ripening the main crop at the base of the plant. Otherwise, handle plants as little as possible to prevent wounds that vulnerable disease spores.

If the weather is dry, provide 1 inch of water a week until two weeks before harvesting, then let the soil dry out a bit. Don’t overwater, or the plants — which can withstand dry spells better than rainy ones — may rot.

Protecting Against Pests

yogesh_more/getty

Southern gardeners are more likely to encounter pest problems than gardeners in Northern areas.

Sweet potato weevils — ¼-inch-long insects with dark blue heads and wings and red-orange bodies — puncture stems and tubers to lay their eggs. Developing larvae tunnel and feed on the fleshy roots, while adults generally attack vines and leaves. They also spread foot rot, which creates enlarging brown to black areas on stems near the soil and at stem ends. Since weevils multiply quickly and prove hard to eliminate, use certified disease-resistant slips and practice a four-year crop rotation. Destroy infected plants and their roots, or place in sealed containers and dispose of them with household trash.

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Fungal diseases include black rot, which results in circular, dark depressions on tubers. Discard infected potatoes, and cure the undamaged roots from the same crop carefully. Don’t confuse this disease with less-serious scurf, which creates small, round, dark spots on tuber surfaces but doesn’t affect eating quality.

Stem rot, or wilt, is a fungus that enters plants injured by insects, careless cultivation, or wind. Even if this disease doesn’t kill the plants, the harvest will be poor. Minimize the chances of disease by planting only healthy slips; avoid black and stem rot by planting resistant cultivars. Reduce the incidence of dry rot, which mummifies stored potatoes, by keeping the fleshy roots at 55 to 60 degrees.

Harvesting

piyaset/getty

You can harvest as soon as leaves start to yellow, but the longer a crop is left in the ground, the higher the yield and vitamin content. Once frost blackens the vines, however, tubers can quickly rot.

Use a spading fork to dig tubers on a sunny day when the soil is dry. Remember that tubers can grow a foot or more from the plant, and that any nicks on their tender skins will encourage spoilage. Dry tubers in the sun for several hours, then move them to a well-ventilated spot and keep at 85 to 90 degrees for 10 to 15 days. After they are cured, store at around 55 degrees, with a humidity of 75 to 80%. Properly cured and stored sweet potatoes will keep for several months.

How to Cure Sweet Potatoes

anightowl 11/2/2013 9:00:27 PM

I have 8 “milk” crates of sweets curing right now. We are lucky to have a bathroom with an outside entrance (the “pool” bathroom”) that doesn’t get used much once things cool down. I wash my sweet potatoes right after harvest before they go in the crates because they are covered in heavy clay when harvested. I make 2 stacks in the (just scrubbed clean) shower and put a portable radiant oil heater in there (no blowing hot air). The shower has a glass door not a curtain so it keeps the heat fairly enclosed. The first day or so it’s kinda humid (about 65%) just from the sweets surface drying but I put a baking pan of water in front of the heater anyway. After a couple of days I get a couple of towels quite wet and lightly wring so they are not dripping. I drape one over each stack, not touching the sweets and the humidity jumps to about 85. The temp holds at about 80-85. I leave the heater on for a week and then I shut it off, leaving the stacks in the shower. It is an unheated room so the temps drop considerably after that – into the 60’s this time of year. After a couple more weeks I take them out and sort the sweets. Some will have soft spots that weren’t apparent before and they get tossed. Then I sort by color (I grow purple flesh ones as well) and size and they get put back into the crates for garage storage. I keep anything bigger around than my little finger – little guys are great just washed and cooked with the skin, and they keep just as well as the big ones once they are cured. This method works really well. I STILL have a few in the garage from the 2012 harvest, and they are still good to eat. Last year I had harvested only some of the beds before I hurt my back. When the rest were finally harvested they went directly into the garage without curing since I didn’t want to do the heater set up a second time. The uncured ones were stringy, boring, and shriveled after a few months – lesson learned – never store an uncured sweet potato. If you have a bathroom in your house that you can make off limits for a week or so this curing method should work for you (obviously the shower will be unusable for the duration but you don’t want anyone using the toilet either – ewww). After the initial cure you can move them to the garage or someplace else that is cool.

How to grow: Sweet potato

At a glance

Ease of culture: Easy
Where: All zones except cold
Best climate: Warm to hot conditions
When: Spring, summer
Spacing: 40cm
Harvest: 4 months
pH: 5.5-6.5

Climate

• Sweet potato likes warm to hot conditions
• Grows best in tropical and subtropical areas where it can be planted year round
• Will produce good crops in temperate areas, but will need at least 4-6 months of warm frost-free conditions to produce a good crop, so plant early spring

Position

• Best crops are produced in open sunny positions with full-day sun, but you can also get a reasonable return in half-day sun and semi-shaded positions

Soil

• Sweet potato needs a deep, loose friable and well-drained soil to allow tubers to develop and avoid rotting in times of heavy rainfall
• Dig over the soil to at least a spade’s depth and incorporate a minimum of 2 bucketloads of compost or well-rotted manure per square metre. Mound the soil into deep planting ridges 40cm wide, to create greater depth and improved drainage
• In heavy soils and heavy rainfall areas, build an even greater depth of soil by mounding rows of garden waste and soil on the soil surface

Planting

• Sweet potato is a perennial vine that covers the ground
• The plants are propagated using cuttings
• Start by planting a healthy sweet potato in the ground or in a pot filled with potting mix when the weather is warm
• Keep it watered and it will start producing shoots which can be used as cutting material
• Take cuttings 15-20cm long, remove all leaves except two at the top, and plant them directly into the soil with the top leaves just above the soil surface
• Keep the soil moist and they will start forming roots within a week. New tubers will form from these roots. The tops will produce lots of green shoots which can also be used as cuttings
• Continue to plant more cuttings as material becomes available

Watering, fertilising and maintenance

• Keep plants evenly moist, but not too wet. Water deeply during dry periods
• Sweet potato needs a good supply of potassium and phosphorous for tuber production. The simplest way to supply this is with compost and an application of a well-balanced organic fertiliser once every 8 weeks during the growing period
• This is a vigorous and often rampant plant during the peak growing time. Trim growth as it escapes using pruning shears or a sharp spade. The prunings can be used as cuttings for new plants or added to the compost heap
• The vines will form roots and potential tubers wherever the nodes (leaf joints) make contact with the ground. This can be further encouraged where appropriate by building soil and compost up around trailing vines

Harvesting and storage

• Tubers are ready for harvest in 4 months from planting in tropical areas and 6 months in cooler zones
• To harvest, pull back vines to reveal their base and then use a garden fork to loosen the surrounding soil and expose the tubers. There can be several tubers ready at each planting spot
• In warm areas, plants can be left in the ground for several years
• In cooler areas, harvest crop before winter
• Large tubers store best. Wash and air-dry for a few days and store in the fridge

Pests and disease

Sweet potato is a very hardy crop that is generally free from pest and disease problems

In the kitchen

Sweet potatoes are delicious baked, boiled, steamed or fried. Add it to curries and casseroles 10 minutes before serving, or use it as a substitute for pumpkin in cakes and pies. Exposed flesh discolours quickly – to avoid this, add it to water soon after peeling and chopping. The young leaves and shoots are also edible and can be used in salads, either steamed or stir-fried.

Varieties

There are two main varieties of sweet potato readily available in Australia. The orange-flesh variety is most common and is sweet and moist. The purple-skinned variety with white flesh has a richer flavour but slightly dryer texture.

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The process for harvesting, curing, and storing sweet potatoes is simple once you get the hang of it. Here’s how to do it.

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Growing Sweet Potatoes

Sweet potatoes are one of my absolute favorite crops to grow. They’re generally pest-free and low-maintenance: plant them late in spring and expect a yield – no matter how the growing season went – by the time fall rolls around. They like it sunny and hot, and watering isn’t essential.

This year was cooler than usual for us and that affected our yield, but with no regular maintenance required for this crop, I’m not complaining.

sweet potato vines

Sweet potato vines also produce well when trellised, because vines scaling the ground will try to put roots in everywhere, which produces a gazillion teensy little potatoes as opposed to several big ones per vine.

Sweet potatoes can be harvested any time tubers have formed (start checking late summer). I’ve found the best strategy is to let them stay in the ground a little while longer, since they’ll continue to grow until a hard frost takes them out.

The key to a superior, sweet taste is allowing them to experience a light frost, and then harvest before the hard frost.

For harvesting, pick a harvest day when it hasn’t rained for a few days. The soil should be minimally moist and crumbly so that you can brush most it off the tubers with a very light touch. You don’t want mud caked onto the tubers because it will make them hard to clean and store.

The harvesting process starts with cutting the vines back so you can get to the soil. If you’ve grown your sweet potatoes on a trellis, then the vines will only be attached at the original root location, which makes it easier to guess where the tubers developed underground. I cut the vines leaving 6 inches above ground to help me locate my treasure.

Vines are cut back to 6 inches. Molly checks our work.

The next step is a delicate one. At this stage, the skins of the sweet potato are very thin and easily damaged. I use my soil knife to carefully and slowly push away the soil to reveal the harvest treat. Then I use the knife to loosen the soil around it, and dig under the tuber, lifting it out gently.

Whether you’re using a knife or a shovel for harvesting, don’t aimlessly stab into the soil, as you’ll risk cutting the tubers in half. Once you’ve found one, don’t pull it out, because the delicate gems will undoubtedly snap in half, leaving the other half buried.

Pieces of tubers won’t store as well as whole, unscathed potatoes. So dig gently, find a tuber, loosen and lift. Having loose soil really helps, so consider growing yours in a raised bed.

Lift carefully and gently

By the way, learning to use a soil knife was one of the best lessons I learned from my old gardening boss and mentor. I still have the one she bought me–my own special left-handed one. It still looks like new today, so it’s a tool that keeps its value.

Don’t forget to cover your garden bed with shredded leaves for wintertime protective mulch and springtime compost!

garden bed mulched with leaves after harvest

You’ve harvested your sweet potatoes and now you’re thinking that you’ll head to the kitchen and make a sweet potato casserole, right? Wrong. Sorry, but the maintenance of growing sweet potatoes–unlike most other vegetables–comes post-harvest.

Curing Sweet Potatoes

Sweet potatoes must be cured for about 10 days. This will heal any damage that occurred to the tubers during harvest so they store longer, and it will also kick off the sugar production process to give you sweeter sweet potatoes.

How to cure? The ideal is an 85-degree room with 85% humidity. What? You don’t have that?!

My easy solution for years running now is this: take plastic grocery bags, punch some holes in them, and fill them with sweet potatoes enough so that there is just one layer of them in each bag. Tie the bags closed and put in your sunniest, warmest window. Leave it for 10 days.

If it gets chilly and your windows are drafty, put a blanket or towel over them when the sun isn’t shining.

Storing Sweet Potatoes

Open your plastic bags of curing sweet potatoes after 10 days. They should be moist and much harder to the touch. If there are any soft ones, these should be tossed out. Now, take single sheets of newspaper and roll up each tuber separately. Stack the wrapped sweet potatoes in a cardboard or wooden box of your choosing (or one that allows aeration), without a lid, and place it in a basement or other room where the temperature is as close to 55-60 degrees as possible, for 6 weeks.

This will even further develop the hard skin and kick off even more sugar production. The newspaper allows aeration and prevents moisture build-up that would otherwise ruin the crop.

makeshift root cellar

After 6 weeks, you can FINALLY cook with them and know that they are at the peak of their sweetness, or you can store them for up to 6 months with the lid on the box, or in a spot not exposed to sunlight. The length of time they store will depend on the degree to which the storage conditions are ideal: temperature (55 degrees), no light, and around 60% humidity.

So this means that if you want to serve that sweet potato casserole at Thanksgiving, you’ll want to harvest your sweet potatoes in early October at the latest. You may not get that frost-kissed sweetness, but the curing process will help sweeten them up.

The process for harvesting, curing, and storing sweet potatoes sounds complicated and time-consuming, but really it’s simple once you get the hang of it. The taste of these homegrown, sweet orange gems that say ‘Thanksgiving’ will be all you need to convince yourself to grow them year after year.

Need more ideas for growing vegetables in the permaculture garden?

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Are you looking for more strategies for your permaculture garden? You’ll find loads of information just like this in my book, The Suburban Micro-Farm.

Are sweet potatoes one of your favorite crops?

Ben Sharda is KCCG’s Executive Director and he has led KCCG for more than 30 years. His practical approach to gardening has played a key role in KCCG’s success. This month, Ben offers tips on fertilizing your plants.

I probably get more harvesting questions about sweet potatoes than any other crop. And, that makes sense because with other crops like tomatoes or lettuce, you can see what you are harvesting and decide when to harvest based on appearance. With sweet potatoes, it is harder to know when to harvest because they are INVISIBLE (well, almost – because they are growing underground).

Sweet potato plants are planted in May and then grow all summer and the vines grow and spread out. Hopefully you have mulched them and kept the weeds out and watered when it was needed. If you have a lot of leafy vines that look healthy, that is usually a good sign that you will have a good sweet potato harvest.

September is the month to harvest sweet potatoes. August is too early and October is too late (usually too cold and rainy). During August, sweet potatoes are getting larger underground. By the second week in September, night time temperatures are starting to cool down which stops the sweet potatoes from getting any larger. I recommend digging one sweet potato plant, early in September, as a test to see what they look like. If they seem small you can leave them a little longer to hope that they get a little larger.

To dig a sweet potato plant, follow the vine back to the stalk that goes in the ground. Then, cut off most of the vine (to make it easier to see where you are digging) and leave the main stalk at 10-12 inches to give you a “handle”. Then clear away the cut vine and measure out about 12” and use a digging fork (sometimes called a potato fork) and dig down and underneath the clump of potatoes. Then pull back on the fork and lift up to raise up the clump of sweet potatoes. Then separate the potatoes and place them in a shallow cardboard box or plastic crate.

A few things to remember:

• Use first any sweet potatoes that may have been accidentally speared during the digging process. They won’t keep very long.

• Store your sweet potatoes in a warm dry place in your house. (65 degrees or warmer)

• Try to dig you sweet potatoes when the ground is dry. (so they will not be covered with mud!)

• Do not wash the sweet potatoes until you are ready to cook them. (gently loosen the dirt off them)

Sweet potatoes are extremely nutritious (and tasty too!). They will keep for a long time and they are very versatile – there are so many ways to prepare and use sweet potatoes in your meal planning. Go to your favorite recipe websites for new ideas on how to enjoy your sweet potatoes.

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