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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Hi Karen,
The only experience I have with voles is seeing them delivered to my door, by our cat, Sebastian, bringing prezzies...
It's obvious the hardware cloth method worked, but I cannot understand the hardware cloth above the potatoes instead of at ground level, under the soil.
I know moles come from underneath, so this may be the cause of confusion. Voles enter from above, on top of the soil?
It's probably a "duh" question I'm asking, & most people get what you're saying, but I don't know the habits of voles entering garden spaces to eat crops.
Much obliged if you have time to reply.
My slips are ready for water and the heat mat speeded that process up incredibly well, so, thankin' you🍠
Hi Chandra! First off - I now grow my sweet potatoes exclusively in pots. I'm not sure if I've mentioned that in this post. As for the hardware cloth, yes, voles will also get in them from above. The method worked perfectly, but the hardware cloth was a bit of a pain to plant through and it made weeding tough. I actually forgot to start my sweet potato slips this year! So just last week I grabbed 4 of my sweet potatoes and stuck them in soil on the heat pad. All but 1 have already started to sprout! ~ karen
I've been growing sweet potatoes from slips using your heat pad method for several years and am very pleased with it. I always have the same problem though: some kind of bug infestation hits the original plant and the slips around week 6 or 7, ie long before its warm enough to plant them outside. This year I've had to place all the slips in an improvised cold frame and hope that they'll.survive. I can't risk them infecting all my other seedlings growing under lights. Any tips.for avoiding the bugs? For the last 2 years, the slips have come from my own previous year's crop and I'm having the same issue as when I purchased organic potatoes. Thoughts?
HI Bev. It's possible they're coming from your soil. What soil are you using? (I've never had a sweet potato bug infestation) ~ karen!
Just saw this reply, 4 months later! Re the soil for slips: its always brand new potting soil. I've learned the hard way not to reuse old soil for seeds or slips! So interesting that you have never had this issue, I have had it EVERY year of the 4 years I've started slips!
wow awesome! i did not know one could grow dsw potatoes in your climate! (or in mine which has cold nights even in the middle of the summer). really great info --thanks-
Q's:
1) what happens if i were to just plant the whole sw potato with all the slips attached? would they make individual new potatoes or just enlarge the one they're on?
2) we absolutely DO with regular potatoes exactly what you do with sweet potatoes: we take the eyes that have started growing even if only a cm, plus about an inch of potato and plant them out in the garden beds with a little soil and thick mulch on top. they grow on their own like gangbusters--barely any water. we leave some of the smaller ones in the bed and they multiply and grow hundreds of new ones!
the thing to be very careful of, is not to plant eyes from potatoes that have ANY kind of blemish from the store, because it could infect your bed with viruses and so forth...
Hi Johanna! The difference is with sweet potatoes is as I said, you only plant the slips which you can simply root in water. One or two sweet potatoes can produce slips for your garden for months if you like. Sweet potatoes won't self regulate if you plant the whole thing. So it's important you only plant individual slips at the proper distance to avoid crowding. Otherwise you won't get any big sweet potatoes. A potato is planted (as you know) whole or with chits (cut portions of the potato). And yes, they grow like gangbusters! ~ karen
Well written instructions & I like how you leave multi options as viable paths. So many garden writers want to make their way the only - the one - true way. (We are creatures that love to make a religion out of most everything) THere are some absolutes in gardening but only a fraction of what appears in the literature.
Don't know if you have ever heard of an old fashioned sweet potato called the "Nancy Hall". It has a most unattractive exterior (a white-ish pale yellow) but golly it is the best tasting sweet potato I've ever had. And as an aside, i find SPs in general have more flavor cold.
There's a great supplier in West Tennesse - George's Sweet Potato Farm. They have dozen's of varieties, and they mail the slips based on timing of your climate. They are a bit pricey given the shipping, but you only have to order them once and your set for a life time. YOu can get all the purple and oriental varieties that you never find in stores or garden centers.
THanks for your great blog!
James
Hi James. Sorry for the delay in my response, lol! I just now saw your comment for some reason. Thanks for the compliments. I was just thinking tonight about how years ago before I had the experience I do now, I thought all those "rules" and "facts" about gardening were actually those: rules and facts. They're not. I'd love to try the Nancy Hall variety, but I'm in Canada and it might not do as well here. I'll keep an eye out for them though. ~ karen!
I had started rooting some sweet potatoes a while back and it was time to start the slips. I though I had tucked away an article and wasn't 100% sure. Could not find the article then found your concise description and am now rooting them.
What sold me on your website was when the subscribe pop-up asked me if I like to sweat, swear and do stuff. I like being outdoors and doing stuff so I am always sweating. And I am always swearing. No, I do not have Tourette Syndrome, but some serious spinal issues which has prevented me from doing stuff, but not swearing ;-). The spinal issues are being addressed. My wife says I have to work on the swearing next.
Anyway, I am rooting purple Korean sweet potatoes. What flips me out is that I live in the largest sweet potato producing state and no one has slips at the local farmers market. Now I just need to keep the groundhogs away from them.
I expect they're keeping the whole sweet potato slip thing secret in your community. It really WAS a secret only known by a few people just a decade ago. Good luck with your spine, your slips and your swearing. ~ karen!
Hi Karen,
I really hope you'll share the liquid eye liner tutorial with us someday though. 😉
Ben
After the first 10 days of curing, do they still need the high humidity for the 30 day cure?
Do I keep them in the plastic box for this part?
Or go ahead, after the 10 days, and put them in a slotted box (better airflow)?
Thanks! :)
You did it again! Everything I need to know about growing sweet potatoes, in one eminently readable post. Thank you, Karen. I grew my own slips the same way last year and was amazed at how simple it was to do! Shout it from the rooftops!
Excellent!! ~ karen
don't know if it went through the first time, so here it comes again.
yeah yeah yeah, didn't read the post yet, i'm sure it's flippin awesome, cause you're flippin' awesome. just needed to get something of my chest...... *deepsigh* in short
I love you.
I've been following you for years now, eagerly looking forward to each post, being amused and inspired along the way. but it was more like a 'yeah, nice, neato, cool' sorta thing. That was then and this is now.
Because NOW I'm at a point in my life, where I actually NEED your wisdom, knowledge and humor. I went from a corporate whore to being a farmer WOOT WOOT WHOOHOOOO.
now I'm reading your posts with a new set of eyes, a new understanding and urgency and hunger and eagerness. it's a little scary. like i need to know how shit works in the real manifest world. and you're the gal i trust the most. and... yeah, i'm just super grateful to have you in my life.
*ramblemodeoff* that's all. as you were :0B
i'm gonna dissect your loofa post now, before i come back to the sweet tatters.
have a fabulous weekend
Karin
This is so funny. I remember your instructions for sweet potatoes from last year. I have a sweet potato that is from my organic farmer. I noticed yesterday it was starting to grow slips. Today I was going to look for your instructions, to my surprise, I find them in my Gmail this morning ❤️. I'm doing the water method. Wish me luck 🤞
Thanks to your post last year, Karen, I actually tried starting some slips with local farmers' market sweet potatoes, then put them outside in a half-barrel. They grew really wild. And harvesting was just a matter of lightly pulling the whole plant out of the dirt. Even a child could do it. Unfortunately, preparing the half-barrel took a bit of time and I planted the slips late, so the harvest was modest. After curing, I discovered that the two largest had started to grow slips. I currently have a few slips growing nicely in pots waiting for the weather to warm up. Whoever knew that growing sweet potatoes would be SOOOO easy!
Oh, I just had a look at the photo of the potted ones again: why did you put rocks around the edges?
And are those strings used by the sweet potatoes or something else that lives behind them?
Thanks 🙏 Kathy
The strings are for tomatoes in behind. And the rocks are just holding down the thermal plastic. ~ karen!
Wow thanks for this post!!
I have grown them successfully one year then the past two crops destroyed by voles! Gurrrr so I gave up! I did use the black plastic (zone 5 here) and had a phenomenal crop with just about 1/3 damaged (I used them in the dog food!).
I am going to try both the heat propagation and the huge black pots! Yay
Hi Kathy! Big pots will eliminate all vole damage. It's great! ~ karen
While this here 'city boy' is not the 'farming' sort, I do hold those who possess the green thumb and more importantly the will to use it in respect and admiration. Thanks for sharing your adventures in soil.
Hi ! I've been trying to grow some sweet potatoes too :) I'm at the water propagation state but I've noticed that part of the potato is starting to rot! What should I do? Leave it as it is? Cut off the rotting part? throw away the whole potato?
It has already started going roots and I can see some small buds forming as well.
It's good I have known how to grow sweet potatoes. I 'm in Nakuru-Kenya (East Africa). Next year I intend to grow them on 1/2 acre piece of land as a trial. If things go well then I will go large scale. Thanks for the tips.
I have now had my tater haul in a covered plastic crate with a damp tea towel in as high of heat as I could get them, probably average of 75 degrees and an average of 70% humidity for 20 days. I do not have anywhere to put them in 55-60 degrees for a month...still too warm here in Texas. The coolest consistent temp would probably be around 68-70. What do you suggest I do to finish curing them? Do I leave them in the plastic crate or should I move them to a cardboard box? When will I know they are ready? Thank you!
I grew 6 large slips and a few tiny ones from one old grocery store sweet potato that had a sprout on it in March. I thought "why not try?". It was headed to the green bin anyway. I lovingly cared for it (including a move) from March until June, breaking off the slips when they got big and letting them grow roots. Luckily the move meant I had a bay window for them to live in. Now I have at least 3 dozen beautiful sweet potatoes (and I have to explain to my Mom why we need to leave a rubber bin in the living room window for 10 days). I wouldn't have tried it it weren't for you Karen. Thanks!
I love hearing that! And good job on curing them. Most people skip that step and it's SO important to get a good tasting, sweet potato. You should try one before they've cured. They aren't sweet at all. ~ karen!