It doesn’t matter if you have a huge vegetable garden or just a pot on an apartment balcony – you CAN grow sweet potatoes. I’m going to show you how and March is the time to start thinking about growing them.
For years I’ve been teaching you how to grow sweet potatoes. How to produce slips, how to plant them, how to keep them pest free, when to shake your fist and swear at them and when to just give them a sideways glance.
Today I’m bringing ALL that information together so you have a start to finish resource for growing these suckers. Because even though growing sweet potatoes is easy – it’s a bit of a thing.
When I first started learning about growing sweet potatoes around 2010 there really wasn’t a lot of information out there on the big, bad Internet about how to grow them. At that time, growing sweet potato slips was a closely guarded secret in the farming community.
It was a mystical, mysterious process much like how to perform a sleight of hand card trick. Or apply liquid eyeliner.
But I read little bits here and there, emailed a few loose lipped Sweet Potato growers with my questions and before I knew it I was growing sweet potatoes in Ontario, Canada. Not exactly the warm climate they’re known for growing in.
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 from whole “seed” potatoes. Sweet potatoes are grown from sweet potato sprouts. Otherwise known as slips.
It all starts with the sweet potato slip.
STUFF YOU WANT TO KNOW
What are Sweet Potato Slips?
Sweet potatoes grow from something called “slips”. Those are the green vines that grow out of a sweet potato when it sprouts. They’re taken off and planted in the ground to create a new sweet potato plant.
**The decorative Sweet Potato Vine you buy in the bedding plant section of the nursery isn’t the same thing – but it will grow a tuber and it can be propagated the same way I show you here**
A single sprouting sweet potato can provide you with at least 15 slips (that’s a low estimate). Those 15 slips create 15 plants, which will give you around 30 lbs or 60 individual sweet potatoes.
Once a slip is a few inches it can be pinched off of the sweet potato and rooted in water or planted directly in the ground.
Some seed stores, nurseries or online stores sell sweet potato slips however, you can just grow your own.
All you need is a sweet potato that hasn’t been treated to stop sprouting. How do you know if it’s been treated? You don’t. You go to the grocery store, buy your sweet potato and hope for the best. Organic is your best bet for an untreated sweet potato.
Once you’ve established your very OWN crop of sweet potatoes you can use your own sweet potatoes for producing slips year after year.
GROCERY STORE SWEET POTATO TIPS
- If you want to try growing sweet potato slips from grocery store sweet potatoes, check for cold damage on them. Cold damage doesn’t show up until a few days after the sweet potato has been exposed to below 55 degree temperatures. On the inside (which you can’t see) the sweet potato will have dark spots. On the outside the sweet potato will have dark discoloured spots and lesions.
Sweet Potato with cold damage
TWO WAYS TO GROW SWEET POTATO SLIPS
Growing in Water
Slips are those vines growing out of the sweet potato. Each individual slip get plucked off the potato and planted in the ground.
The Old Way
With this method you’re generally safe to start your slips 6 weeks prior to when you want to plant them out.
This is how I grew my Sweet Potato slips for the first 10 years of growing them:
- Place sweet potatoes in a glass jar of water. You want half of the sweet potato under water and the rest not. The part under water will grow roots and the part above water will grow sprouts (known as sweet potato slips). If your sweet potato is too skinny you can use toothpicks to keep it from falling right down into the jar of water.
- Put the jar with the sweet potato somewhere WARM. Over 80 degrees Fahrenheit is ideal. And the warmer the better. I have a dining room cupboard that’s next to a heat vent. I know the cupboard always gets warm because of the vent so I put my sweet potatoes in there. At this point the sweet potato doesn’t need any light. Just warmth. Now just leave the sweet potato and wait.
- It could take as long as a month or more for the potato to start growing “slips”. Just keep checking them every few days to see if they’ve started to sprout.
- They might grow roots before they grow slips so check for those too. Depending on the mood of the sweet potato, slips will start growing out of it in anywhere from a week to two months.
As you can imagine, this whole maybe I’ll sprout today, maybe I’ll sprout when it’s way too late to plant me, attitude of the sweet potato gets old fast.
So a few years ago instead of starting my sweet potatoes in jars of water like I normally do, I tried something new. I planted them in a pan of soil. Nothing fancy, just an aluminium roasting pan from the dollar store that I poked holes in the bottom of for drainage. Then I sat it on a seedling heat pad and waited.
Growing in Soil
The New Way
1. Place whole sweet potato(s) lengthwise in a pan of soil so the soil comes halfway up the side of potato.
2. Place the pan on a seedling heating mat.
3. Make sure the soil stays moist and wait for it to produce roots / slips in 2 weeks or less.
It’s the magic of the heat pad. And also the magic of growing in soil (mixed with compost) that has actual nutrients in it.
Growing in soil on a heating pad just gives you slightly stronger slips (less likely to croak on transplant) and a better guarantee of growing within a few weeks as opposed to a few months.
The slips can either be planted directly into the ground or left to root in water until the weather warms up.
Because sweet potatoes are the heat loving little things that they are you can’t put them out in the garden until it’s warm out. For me in zone 6b that means I don’t plant my sweet potatoes out until June 1st.
If your sweet potato has plenty of slips but it isn’t warm enough to plant them out yet, pull them off the sweet potato and let each slip root in water.
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.
You can 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 sweet potato slips 1-2 weeks sooner than if you don’t use plastic.
1. Lay black thermal mulch (plastic) on area for planting 2 weeks before setting out. Sweet potatoes need full sun so make sure your area has that.
2. Cut a circle in the plastic and push one slip in. Make sure the slip has contact with soil all around.
3. Plant 1 slip per square foot. They can be planted with 1 foot between rows, but 16″ is better if you have the room.
4. Keep the sweet potatoes well watered throughout the summer. Using the plastic eliminates the need to weed.
5. Harvest sweet potatoes before the first frost. Once the weather cools down they won’t grow anyway.
Planting the slips closer than 1′ together will reduce your yield and produce much smaller sweet potatoes.
Protecting From Pests
Voles, moles, mice and other things that tunnel, burrow and generally bother are more in love with sweet potatoes than you will ever be. And one tiny little vole family will eat every single sweet potato you grow if you don’t protect them.
You can protect sweet potatoes from pests in two ways.
60 litre pots that measure 60 cm across. Planted with 2 slips per pot.
- Grow them in very large pots where rodents won’t have access to them. Which is also a perfect way to grow sweet potatoes if you only have a sunny apartment balcony or limited space. You’ll notice in the photo above that even I even use black plastic to warm the soil when growing in pots.
You can 1/4″ hardware cloth from most hardware stores. If you can’t find it locally, Amazon carries it.
2. Cover your sweet potato bed with 1/4″ 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. To 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.
The first season I did this I was worried the voles would tunnel under the raised beds to get to the sweet potatoes, but for whatever reason, they don’t.
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 to Harvest
Near the end of their growing life sweet potato vines will start to yellow. This is a GOOD sign! They’re ready to harvest.
Harvest your sweet potatoes once the weather gets cool in the fall. In my zone of 6b I generally dig them up in the first 2 weeks of October. Don’t water the sweet potatoes for 1 week prior to digging them up. This allows them to dry out and come out of the ground cleaner.
If the vines get touched by frost and start to turn black the sweet potatoes can rot quickly so dig them up right away!
- 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. Sweet potatoes bruise easily.
Curing & Storing
Harvesting sweet potatoes doesn’t end with digging them up. Once you dig them up you have to let them dry in the sun for a few hours. Then they need to be brought inside and cured for 10 days, and then cured some more for another month or so.
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.
The optimal conditions for curing sweet potatoes are in an 85 degree room at 85 percent humidity. Um … sure.
Don’t worry. All you need to do is get as close to the idea conditions as possible. You can do this relatively easily believe it or not.
- 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 55-60 degrees 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.
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.
SWEET POTATO TIP SHEET
- Start sweet potato slips 6 weeks prior to planting out.
- 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 1/4″ 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
Once you have a whack of sweet potatoes that you’ve grown yourself, if stored in good conditions, they’ll last you into March or even April.
And just like that ALL the card trick has been revealed. I’m like the Penn and Teller of the sweet potato world. Now go forth and grow.
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