A step by step guide on how to grow sweet potatoes & how to start slips. Growing sweet potatoes used to be a closely guarded secret among farmers. A mystical, mysterious process - like how to perfectly apply liquid eyeliner. Not anymore!
I've successfully taught thousands of you how to grow luffa in a cold climate (zone 6) and sweet potatoes (known as Kūmara where it's hugely popular in New Zealand) are no different.
It can be done and you can get a HUGE harvest even in a short season - you just need to follow the steps.
In 2010, when I first started growing sweet potatoes (Ipomoea batatas), there was almost no information on the Internet about it. At that time, growing sweet potato slips was a closely guarded secret in the farming community.
Not anymore.
Table of Contents
Two ways to grow sweet potato plants
🌱 It starts with growing the slips. 🌱
In order to grow sweet potatoes, you have to first grow sweet potato slips. These are the sprouts that come off of the sweet potato.
Every slip will grow into a sweet potato plant that will produce around 2 pounds of sweet potatoes
1. IN WATER
2. IN SOIL
Sweet potatoes sprout after they break dormancy just like the perennial plants in your garden do. These sprouts are called slips and they're what you use to grow sweet potato plants.
You can encourage your sweet potato to break dormancy by putting it in a warm room in either a glass of water or some soil.
Water Method
With this method you're generally safe to start your slips 6 weeks prior to when you want to plant them out.
STEP 1. Place sweet potatoes in a glass jar of water with half the sweet potato under water and the rest not. The part under water will grow roots and the part above water will grow slips.
STEP 2. Put the jar somewhere WARM - over 80℉ is ideal. Now you wait about a month for it to root and sprout.
STEP 3. Once the slips are a few inches long they can be pinched off of the sweet potato and rooted in water or planted in 4" pots.
STEP 4. Slips can be planted outside once the soil temperature is 65ºF (or 18ºC).
Soil Method
The soil method produces slips more quickly. With this method you're generally safe to start your slips 4 weeks prior to when you want to plant them out.
STEP 1. Place whole sweet potato(es) lengthwise in a pan of soil so the soil comes halfway up the side of potato.
STEP 2. Place the pan on a seedling heating mat.
STEP 3. Make sure the soil stays moist and wait for it to produce roots / slips in 2 weeks or less.
STEP 4. Once the slips are a few inches long and you can either put them in a glass of water to root, or plant them directly in soil to root. Either way is fine. Rooting in a glass jar takes up a lot less space than putting each slip in a 4" pot with soil.
STEP 5. Slips can be planted outside once the soil temperature is 65ºF (or 18ºC).
TIP! It's the warmth of the heat pad that speeds up the sprouting process.
How to plant
Sweet potatoes will be one of the last things you plant in your garden. They must go in later than peppers, tomatoes and other heat loving plants because sweet potatoes need more than just warm weather. They need warm soil as well as warm air.
STEP 1. Apply a couple of inches of compost to the top of your soil. You can also use a slow release fertilizer; I use Gaia Green's organic 4-4-4 all purpose fertilizer in my garden.
STEP 2. Lay black thermal mulch (plastic) on the planting area 2 weeks before setting out. Sweet potatoes need full sun so make sure your area has that.
STEP 3. On planting day cut a circle in the plastic and push one slip in. Make sure the slip has contact with soil all around. Repeat for all your slips.
STEP 4. Proper spacing for planting is 1 sweet potato slip per square foot. HOWEVER, I find spacing of 16" between sweet potato plants increases your yield & the size of your sweet potatoes.
STEP 5. Keep the plants well watered throughout the summer. Using the plastic eliminates the need to weed and helps retain moisture.
STEP 6. Harvest before the first frost. Once the weather cools down they won’t grow anyway.
* Speed up your soil warming by laying a layer of black thermal plastic in your garden bed. I use biodegradable plastic made of cornstarch that just decomposes on the soil by the end of the season. It will heat the soil up by as much as 10 degrees which means you can plant the slips 1-2 weeks sooner than if you don't use thermal plastic.
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Growing in beds
Growing in containers
If you grow sweet potatoes in the ground you may find voles & mice get to them before you do. Hardware cloth can help with this. If you can't find it locally, Amazon carries hardware cloth.
- Cover your sweet potato bed with ¼" hardware cloth. Grow your sweet potatoes in a raised bed with wood sides. After laying your plastic down, staple hardware cloth around the edges of your bed.
- Plant the slips you have to punch a hole into the plastic with a pencil and push the slip through the hardware cloth, plastic and into the soil. THIS IS A PAIN. But it eliminates 100% of rodent damage.
I grow all of my sweet potato plants in containers.
- Plant 1-2 sweet potato slips in a 60 litre pot that measures 60 cm across.
- Remember to keep the pots watered as they'll dry out more quickly than a garden bed.
Once your plants are well established you can also harvest and eat the leaves.
Use them in: salads or cook them like you would spinach or chard.
This video shows my sweet potato harvest in 2016 after I tried using the hardware cloth the first time in a raised bed in my 40' x 40' community garden plot. In this video I'm using regular thermal plastic, not the biodegradable plastic.
How & When to Harvest
Near the end of their growing life sweet potato vines will start to yellow and croak. This is a GOOD sign! They're ready to harvest.
- Cut the tangle of vines away, leaving only a few stubs to let you know where the plants are.
- Using a shovel or digging fork, dig em up! Honestly, the most fun crops to grow are the ones that grow underground because you have NO idea what you have until the day you dig them up.
- Be careful when you're digging them and pulling them out. They bruise and break easily.
- Once they're all dug let them sit in the sun for a few hours to dry and begin the curing process.
If the vines get touched by frost and start to turn black the sweet potatoes can rot quickly so dig them up right away!
How to Cure & Store
Curing
Sweet potatoes need to be cured for 10 days in an area that is 85ºF with 85% humidity. Getting those conditions at home probably seems difficult but just get as close to those ideal conditions as you can.
Why do you have to cure sweet potatoes? Curing toughens the skin so they keep longer and it develops their distinct sweet flavour. A sweet potato dug straight out of the ground won't taste sweet at all! Try it.
Here's how:
- Put your sweet potatoes in a rubber bin with the lid offset so it isn't completely sealed off. Store this near a heat register, wood stove or sunny spot. This will create conditions as close to perfect as you can get in most houses. DO THIS FOR 10 DAYS.
- After the initial 10 day curing period move your sweet potatoes to an area that is between 55-60ºF for one month. This develops their flavour. After 1 month they will have developed their sweet potato flavour which will get even stronger as time goes by.
Storing
Store sweet potatoes in an area that doesn't get below 50 degrees in a container that breathes like a slatted wood box or a burlap sack.
How many sweet potatoes do you get per plant?
2 lbs or 4 sweet potatoes per sweet potato plant.
1 sweet potato plant will produce about 4 large sweet potatoes, or 2 lbs of sweet potatoes. Some varieties will produce 6 or more per plant.
The plant usually creates 1 very large sweet potato, along with a few smaller ones.
A single sprouting sweet potato can provide you with at least 15 slips (that's a low estimate). Those 15 slips will create 15 plants, which will give you around 30 lbs or 60 individual sweet potatoes.
Where to buy slips
If you don't want to grow your own you can buy potted sweet potato plants at many garden centres now and you can order live slips online.
Growing from store bought sweet potatoes
To grow your own slips all you need is a sweet potato that hasn’t been treated to stop sprouting which you can get at the grocery store.
How do you know if it’s been treated? You don’t. You go to the store, buy your sweet potato and hope for the best. Organic is your best bet for an untreated sweet potato, but both organic and "regular" store bought sweet potatoes have produced slips for me.
Tips on picking a sweet potato from the store to grow
- Check for cold damage. If the sweet potato has been exposed to below 55 degree temperatures it will probably rot rather than sprout. Cold damage presents with dark marks and lesions.
- Bigger isn't necessarily better. Small sweet potatoes, in my experience, have produced more slips than larger ones.
- Ask if they were grown locally. Locally grown means it will grow well in your region.
Sweet Potato with cold damage
Once you've established your very OWN crop of sweet potatoes you can use those for producing slips year after year.
Are ornamental sweet potatoes edible?
You may have noticed that your ornamental sweet potatoes also produce tubers. These tubers are edible but not delicious.
The good news is you can propagate ornamental sweet potato vine the same way as regular sweet potatoes! Just dig up the decorative sweet potato tuber in the fall, store it in a cool room, and then encourage it to grow slips in the spring. These slips can be planted directly outside or rooted and potted up for later planting.
Varieties of Sweet Potatoes
The most popular sweet potato variety by far is Beauregard and it'll be the easiest for you to find. But there are a lot more varieties than that.
- Beauregard* (best all around sweet potato variety)
- Georgia Jet (short season variety)
- Jewel (longer season but still doable in colder climates)
- Garnet (a purple variety with purple skin and flesh)
- Stokes (bright purple variety that retains its colour after cooking)
- Covington (a standard variety that grows well in cooler cliimates)
*this is the sweet potato I most often grow.
Note: I have successfully grown all of the above (with the exception of "Stokes") in my Canadian garden. I just haven't tried Stokes, but I'm sure it would be fine.
Sweet Potato VS Regular Potato
To clear up any confusion, sweet potatoes don't grow like regular potatoes. A regular potato is a tuber, a sweet potato is a root.
Regular potatoes are grown by planting whole "seed" potatoes into the ground. (here's my guide on how to grow regular potatoes)
Sweet potatoes are grown by planting only the sprouts aka slips that grow from the sweet potato.
The Start to Finish Guide to Growing Sweet Potatoes.
How to successfully grow sweet potatoes whether your garden is big or small.
Materials
- Glass of water
- Foil pan with soil
- A sweet potato
Tools
- Heat mat
Instructions
- Start sweet potato slips 6 weeks prior to planting out.
- Rest a whole, undamaged sweet potato in soil and set on a heating mat. Slips will start to grow in around 2 weeks. When around 5", break slips off of sweet potato and plant out or root in water.
- Rooted AND unrooted slips can be planted directly in the soil.
- Speed up how quickly you can plant your slips outside by laying down thermal plastic
- To prevent vole/mole/mouse damage either grow sweet potatoes in very large pots or grow in a raised bed with wood sides and ¼" hardware cloth across the top.
- Dig up sweet potatoes when the weather cools in fall.
- Cure sweet potatoes at 85F and 85% humidity for 10 days.
- Cure another month at 55-60F allowing potatoes to develop sugars.
- Store long term in vented crates or burlap bags at no colder than 50F
Sweet potatoes can be harvested 4 to 5 months after planting.
You get around 4 sweet potatoes per plant. Usually one very large one and a few smaller but still substantial ones. Some varieties under the best conditions will produce even more.
Any potting soil will work well. It has the nutrients you need. If you are reusing potting soil you'll need to amend by adding fertilizer. Adding a 4-4-4 fertilizer or a few inches of compost to the top of the depleted potting soil will revive the soil. I also use native garden soil in my sweet potato containers.
Yes, that's exactly how you grow them but you don't plant the entire sweet potato. You let the sweet potato sprout in a warm place, pull the sprouts off when they're a few inches long and then root or plant those in soil.
May or June are the best months to plant sweet potatoes outside when the soil at planting depth has warmed up to 65ºF (or 18ºC).
Yes! Sweet potatoes do really well in beds, buckets or pots. Buckets and pots are especially good for growing sweet potatoes because they keep the soil warm and prevent moles and mice from eating the growing tubers.
Once you have a whack of sweet potatoes that you've grown yourself, if stored in good conditions, they'll last you into April or even May.
You can turn them into my personal favourite guaranteed crispy Sweet Potato fries with a Sriracha/mayo dip, Sweet Potato soup or sweet potato casserole.
Now go forth and grow.
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Wendy Crowley
I will definitely try the rooting method on a heat mat, since I am currently seeding a bunch of things. Could you possibly pass on your source for seed potatoes? I’m north of Peterborough & am having trouble getting any. My usual source is not attending the local farmer’s market this year. Thanks, for all your info, inspo & humour.
Wendy
Kathy B
Thank you for your info on growing slips in soil, will be trying that this season. I used to grow in water with patchy success so I have been buying them from mail order. Sweet potatoes are easy to grow and I live in zone 5. The taste is so much better than store bought, so much so that I skipped growing them 1 season and got scolded by my Great Aunt because she wont go back to those tasteless things in stores. When planning my garden my family teases me that I better be growing sweet potatoes so I don't get in trouble again.
Belinda
Karen,
You really make a difference in our garden. I read this last year and ordered our slips from an Ebay vendor in GA. The Sweets stored beautifully and we finished the last of them in March. I ran into a problem with our winds bashing the young vines against the holes I had cut in the plastic and it caused me to loose a few before I removed the plastic all together. This time, I'm going to run long plastic strips down the middles in the windward direction and weight them down with flat rocks. Our summers have their cold, rainy days and the vines on the South side of the box grew the larger potatoes. I'll be planting them on the south sides from now on, although I'm glad I kept the ones that stayed cooler and grew thinner, as they were very tasty, roasted up skin on, and sliced onto fall salads with a honey vinaigrette and goat cheese. Thank you for this great step by step lesson.
Christine in BC
Hi Karen
I always love your posts, and last year you inspired me to try growing my own sweet potatoes. I grew my own slips, I planted my lovely, leafy slips in a their own raised bed, put the black plastic down and I waited. Over the summer, they seemed to be doing well, there were lots of leaves and it was growing well. In the fall when I went to harvest all of my sweet potatoes, imagine my surprise when all there was at the end of the roots was nothing but sweet potato colored strings! I meant to take a picture to send to you. I did laugh but I'm scared to put aside that much of my garden for nothing! What did I do wrong?
Sarah
Voles tunneled under and into my raised beds this spring already and are pulling under most of the peas. It's the first time on 20 years.
Otherwise awesome sweet potato info. I hope to NOT loose the potatoes and/or the sweets.
Amy
I think you were reading my mind, as I was just thinking about trying sweet potato gardening for the first time and am in New England US zone 5 climate. Thanks for all the tips!
Victoria
When you say “check for cold damage” do you mean that if they do have cold damage they won’t sprout?
Olga
Thank you. I was going to do some research to try grow my own sweet potatoes this year. I bought some at the store and one of them actually started sprouting slips lol. Going to throw in in some tin foil with dirt tomorrow and wait 😀
Deb Gerry
I have a couple plants I saved and over wintered from last year's garden for slips for this year. Tops died off (is hard to keep them warm enough) I was going to toss, but the ROOTS look great so I repotted and have them on morning sun windowsill. 2 other plants in pots struggling but alive. Do I just toss the ones with no apparent plant life above ground or give them more time?
Carlos
It is my first time growing sweet potatoes and I saw a video of someone growing regular potatoes and they said you start with a little bit of soil in the container and as the plant grows you keep adding more and more soil on top and continue burying the plant because potatoes grow up. Is this true for the sweet potatoes also? Or do you just plant in the ground and let the foliage grow?
Karen
Hi Carlos! Potatoes and Sweet Potatoes grow differently. When you plant potatoes, you plant the actual potato (called a seed potato or a chit if it's a chunk of a potato) around 18" deep in the soil. And then yes it grows upwards from there, with the plant using the potato as energy to grow. But with sweet potatoes you're planting a sprout. So you plant it into the top of the soil just like you would any other seedling or plant. :) ~ karen!
Rob Halsall
Thanks for posting this! I've tried your technique for a few weeks now and all my sweet potatoes are throwing roots out like mad, but I don't have a leaf (or even a green slip) yet. Is there a chance I've missed something? Last week I tried taking one out with its roots and placing it in the glass of water, but the roots are just carrying on growing. Maybe this is normal and I need to be more patient. :-) Any comments are greatly appreciated! Thanks in advance!
Karen
HI Rob. This is perfectly normal! Just let them do their thing and make sure they have heat. They'll eventually start putting out slips. It can take a while. :) ~ karen!
Jeff
It is 3 June, is it to late to start to grow snips from a sweet potato and harvest in the fall?
Karen
Hi Jeff. It depends on how quickly you can grow them, but at this point you'd be better off running around trying to find pregrown slips. It's not too late to plant, but it is getting late to try to grow slips. ~ karen!
Elaine R Finch
Hi, I hope by now you have your sweet potatoes growing well but if not, I always add a little hydroponic nutrients to the water I have my sweet potatoes rooting in and they have grown huge green slips.. ready for the garden.
Diane
I have read an abundance of the comments. I love Yams, I know there is a difference between the sweet potato and the yam, and the regular potato. Here you speak about sweet potato, I am looking for the yams, are they grown the same way? Thanks Diane
Margaret K.
True yams are tropical and are unrelated to sweet potatoes. They are not often grown in North America because they don't like our climate. Also, they are pretty blah in taste. What some Americans call "yams" are sweet potato varieties that have a firm, comparatively light-colored flesh. Sweet potatoes actually come in many colors. Some of the ones that have been developed in Asia have purple or white flesh.
You grow the "yam" type of sweet potato just like Karen describes here. But I like the ones with a really orange flesh best.
Geraldine Winterhalter
Hi, I live in a country where sweet potatoes are considered very exotic, only for foreigners like me and far too expensive for the local population. I tried growing slips in water and nothing happened. Then my sister-in-law came to visit and explained that they had probably been sprayed with an inhibitor to prevent them sprouting. Any ideas how I can get past this problem.
Geraldine
Karen
Hi Geraldine. Unless you find someone there who also grows their own sweet potatoes then using store bought sweet potatoes is your only route to getting slips. Even if a potato has been sprayed with inhibitor you can get lucky and find one that will sprout. You can also try my method of sprouting in soil. Don't forget it can take a long time for them to sprout if they're being particularly stubborn. If you just stick it out for one year and try everything possible, you'll have your own crop which will make sprouting every year after that MUCH easier. ~ karen!
AJ Kamradt
I grew sweet potatoes in a pot last year but all I got were roots and exactly 1 sweet potato. I live in Az so heat wasn’t the problem, nor water. The plants were absolutely beautiful and they were all over the place but no potatoes
Any idea why the roots never developed into potatoes
Karen
It depends on how many sweet potatoes you put in and how big the pot was. They do NOT like to be crowded. I don't know how they know, but they do. One slip per pot unless it's really BIG. Like the size of a half whiskey barrel. That would be my first guess. The next would be making sure the soil in the pot had fertilizer in it and wasn't years old and depeleted. ~ karen!
Margaret Gove
Hi
Sweet potatoes come from America, and they are irradiated to prevent shooting. Unless you are lucky, and can find organic ones, we are out of luck!
Michelle
Not true at all. Wash them thoroughly with soap and warm water. Let them dry before you put them in the soil. Once dried, lay the sweet potato in the soil..lighty water them, cover it, and place heat mat underneath it. And wait. It takes a while but will grow the slips to your desire. Believe me! I did it. My sweet potato wasn't organic either.
Barbara B
I tried an organic and non-organic sweet potato. The non-organic didn't do anything after six weeks except get mushy while the organic one has produced slips (the water method). Next year I'll try the soil/heating pad method.
Rinny
I read somewhere they recommend using organic when trying to start from a store bought, as the non organic sprays with something to prevent it from sprouting.
Amie
Thank for all the info! I started a sweet potato in soil and one end started to rot and get mushy. Can I just cut the end off and leave it or do I need to replace it with a new potato? Thanks!
JPB
If one end started to rot, you had the soil too moist. Cut off the rot and place the tater in soil that will drain, you can even have some of the tater exposed to sunshine to encourage growth.
carla
Question about the soil...I did one in soil and one in water last year. The soil one grew slips just fine, but I got gnatty sort of maybe fruit fly like bugs bugging my sweet potato soil. Any tips for how to keep the bugs away?
Christina
Those are fungus gnats. Put a thick layer of vermiculite on top of the soil to keep them from being able to lay eggs.
Alanna Farmer
I found an overlooked sweet potato that had sprouted and stuck it in the window to see how it would fare. I have used the toothpick and water method but I think I like this one better. The sweet potato is starting to desiccate so I think it's time to introduce it to a bit of dirt. Thanks for writing this - enjoyed reading it
Karen
Thanks for saying so Alanna! ~ karen
Mike
If my store bought sweet potato is already sprouting can I cut these off with a slice of the potato & start these as slips in water? Will such slips produce sweet potatoes or just vines and do I have to produce slips from blind shoots not yet formed?
Karen
Hi Mike! If you have slips growing from store bought sweet potatoes they'll grow just fine. You can either root them in water or put them straight into a pot with soil. Either way they should do well. Then all you have to do is keep them alive until spring or whenever you can plant them outside depending on where you live. ~ karen!
Shellie
In regards to the vine question, I saw someone bury part of a vine in an adjoining container, and it rooted and grew sweet potatoes in that pot too. Once it firmly rooted, they cut the new vine away from the mother plant, just like with strawberries, but with big fat sweet potatoes instead. Can't wait to try it myself. I plan to keep one growing all year in a container and harvest the greens for salad to keep them in check. Karen, any experience with that? How much root or greens can you harvest without overly stressing the plant?
Paulina
I had to look up how to *plant* the slips that accidentally sprouted in my pantry, and yours came up, alongside the more science-y version, and a bajillion varieties of sweet potatoes, including the hardy short season kinds that grow most everywhere in the United States and parts of Canada at https://www.sandhillpreservation.com/sweet-potato-growing-information
The latter, for someone like myself, who is trying to start growing enough food to sell at my farmers' market, is a lot more in-depth, but this post opened a rabbit hole of a time sink for me. I'll have to spend days browsing articles now. Thanks a bunch. /s
I'll enjoy it. :)
Diane
Just found this will be trying the new way this year it sounds so much better thanks. Cheers Diane. France
Karen
Good luck Diane! Mine slips are growing wildly now. ~ karen!
Elizabeth
I realize it's an old post but...the story about starting slips being a 'closely guarded secret' made me BUST OUT LAUGHING. I was fortunate to grow up in the Carolinas and everyone, I mean EVERYONE with any garden know how could tell you how to start slips. I was raised watching my grandmama start them for the garden, then keep one and put it in a jar hanging in the kitchen window and it made the prettiest vine in the kitchen all summer. A shame people in other regions didn't inherit that information.
DLee
Yes, NC is the sweet potato capital of the western hemisphere. We grow 60% of the total US production, thats 50% more than the other 49 states combined. There are multiple potato warehouses in my region, one of them can store 2 million bushels of sweet potatoes. You can even pick your variety, if you know what you like. I like Murasaki and Bonita (both are white sweet potatoes). Covington is one of the more popular orange potatoes.