Growing sweet potatoes: A Step-By-Step guide

It’s easy to understand why more and more of us are wanting to grow sweet potatoes in our own kitchen gardens. You only have to taste a sweet potato pie in the Autumn, or sweet potato French fries, or simply an oven-baked sweet potato with a strong cheese dressing to realize why this fantastic, delicious and sweet root vegetable is so popular. 

Whichever way you prefer to enjoy them, sweet potatoes have become more and more popular on our dining table.

The question is how easy or difficult is it to grow sweet potatoes? 

How do you start to have the best chances of succeeding? 

This article offers easy to follow advice and tips, so you can start to grow sweet potatoes successfully in your own garden.

A delicious root vegetable and a decorative plant too

Sweet potato – Ipomoea batatas – is a quick growing plant with large, decorative leaves. You can grow them in large pots (around 5 liters), in a greenhouse or directly in the ground outside.

If you start to grow sweet potatoes sprouts (“slips”) in a pot, it’s important – actually essential – to plant them out into the ground before the roots become too large in the pot and the plant ends up becoming pot-bound.

If the roots start to wind around themselves this can lead to a deterioration of the quality of the plant.

The roots need to develop and swell – they eventually become the actual sweet potato.

With warmth comes a bigger harvest

The climate in which you live will determine how long it takes for the plant to mature.

In the warmth, it will take around 3-6 months from planting out sweet potato slips until you get a harvest. 

And sweet potatoes really do require warmth. Outdoor temperatures should be at 16 degrees celsius before you plant them out. They are very sensitive to frost.

Originating in Central and South America, sweet potatoes thrive in warm, moist climates.

But that does not mean that you cannot grow sweet potatoes in your own garden, even if you are living in a cooler region! You just need to give them the right conditions to thrive.

Sweet potatoes are not related to regular white potatoes. They actually come from the family of herbaceous vines called Convolvulaceae. The more commonly known name is bindweed, or Morning Glory.

There are many different kinds of sweet potato. They are easy to recognize with their elongated shape, orange colored flesh and pinky-copper colored skins.

You can experiment with varieties such as Bellevue, Orleans, Erato, Jewel, Evangeline and Beauregard. Ask at your local farm store or market what mature sweet potatoes are available for purchase.

A step-by-step guide – How to grow Sweet potatoes

Sweet potatoes are not grown from seed. They are grown from”slips” which is a shoot that comes from rooting a mature sweet potato.

1. Start around the end of february, beginning of March by buying about 10-12 mature sweet potatoes. Buy organic from a nursery or a local farm shop. Visit your local suppliers and look at the different varieties they offer. 

Regular sweet potatoes from a supermarket may have been treated with a waxy coating which will make it more difficult to grow healthy slips. Buying organic means they will be untreated, and will often yield better results.

Make sure each potato is free of discolored patches, is firm to touch, and has not already started sprouting.

From your sweet potatoes you need to grow slips (shoots). There are 2 easy methods to start growing slips. One uses water and the other soil. You will then plant out these slips into your garden.

2. To try the water method, fill a large jar or glass with water. With the blunt end of the potato facing down, insert 3 or 4 toothpicks horizontally in the top half of the sweet potato.

3. Use the toothpicks to suspend the potato over the top of the jar with just over half the potato being submerged in the water.

4. Place the potato in the warmest part of your home or sunroom. Preferably close to a radiator. The potato needs warmth and moisture to develop.

5. Replace the water in each jar with fresh water every week. 

6. If you prefer the soil method, place potato lengthways on a deep tray filled with fresh, nutritious, loose soil. The bottom half of the length of the sweet potato should be buried in the soil. You can also use a 5 gallon grow bag or pot with holes for drainage in the bottom. Place the tray or pot in a sunny position in the window or in your sunroom.

7. Alternatively, place potatoes directly in the soil in raised vegetable plantors in the garden in the same manner. Again, ensure the soil is fresh, nutritious and loose. If the soil is too firm or compact the roots will not be free to develop fully.

8. If planting outside ino your vegetable garden, dig a trough and plant one potato every 30-40cm apart. The top half of the potato should be sticking up above the soil.

Press the soil around the potato to expel any air pockets, but not so hard that you compact the soil too much. Water well.

9. Cover the potatoes in the soil with garden fabric to retain warmth, or ideally have the plantors under glass while the potatoes start to sprout.

10. Whether you have chosen to grow the slips in water or in soil, after about 2 weeks there should be shoots coming out of the side of your sweet potato. These shoots will form leaves whilst the bottom of the shoots will grow a white tangle of roots.

The shoots are known as “slips”.

11. Each sweet potato will yield on average 4 to 5 slips.

12. After about 2 months the slips should be a good size, and you can pull them away from the potato carefully, so both slips and it’s roots are intact.

13. Plant the slips into soil in the ground, about 30cm apart, in rows. Each row should be about 80-90 cm apart. Plant out the slips from around April to May, or as soon as you know that the last frost is over and outdoor temperatures have reached at least 16 degrees celsius.

14. Ensure soil is rich in nutrients and loose, so the root system can establish itself easily and quickly.

15. Each slip will grow into its own potato plant.

16. Your sweet potatoes should be ready to harvest after around 100 days from the time you plant out the slips. The leaves of the plant should have started to turn yellow and wilt.

17. Gently pull the plants out of the ground and loosen the soil with a garden fork to find your crop of sweet potatoes. 

18. Success is determined by how many healthy sweet potatoes each plant yields. You can expect 1-1.5 kilos of potatoes per plant.

19. Be sure to discard any sweet potatoes from your crop that are soft, or that have turned a brown or black color. These should not be eaten.

20. Do not store your sweet potatoes in the fridge. Store at room temperature in your panty. Store for a couple of weeks before eating and you will give the starches a chance to turn into sugar, giving a stronger, more buttery flavor to the potato.

Common questions asked when growing your own sweet potatoes

How many sweet potatoes should you expect from one plant?

One sweet potato can yield as many as 15 slips but it is more common to get around 5-8 slips per potato. 

Each slip will grow into one plant. 

One plant should provide around 8 to 10 beautiful sweet potatoes.

Results of course will depend on the growing conditions and how much care you are able to give your plants. 

Sweet potatoes are not the easiest root vegetable to grow, but often one of the most rewarding and fun as you really are creating the whole process yourself, from start to finish.

What type of soil is best for growing sweet potato plants?

The better quality soil you have, the more successful your crop of sweet potatoes will be. Soil that is good quality , light textured and free of weeds is essential.

If you soil is too heavy and compact, add some sand. This will aid in water drainage. Ensure your soil is nutritious buy adding a dose of fertilizer containing phosphorus and potassium.

Can I use store bought sweet potatoes to start growing sweet potato slips?

You can if you are buying from a wholefood market where produce is organic.

For optimal results the sweet potatoes you start with should be organic and untreated in any way. Sometimes regular supermarket sweet potatoes have been treated with a waxy coating and this can inhibit the growth of slips.

What shall I do if my sweet potatoes have grown many slips, but it is too cold outside to plant them out?

If the temperature outdoors has not reached a minium of 16 degrees celsius and you are not sure if the last frost is over, do not plant the baby slips out yet.

Simply remove the slips carefully from your sweet potatoes. Place each slip in it’s own individual glass filled with water and place on a sunny window ledge.

The leaves should all be above the water level. Leave the slips in the water for a couple of weeks to root. When it’s warm enough, plant them out into your vegetable garden in a sunny spot.

How often should I water my sweet potato plants?

Sweet potato plants must have water to thrive. Water thoroughly and deeply a few days per week, rather than surface water everyday. This way the water will reach the deep roots

What should I do if I see fungal disease and leaf spot on my sweet potato plants?

Sweet potato plants can be attacked by fungal diseases and by leaf spot, so keep a close eye on your plants. Learn how to spot these problems and invest in an organic pesticide by speaking to your local suppliers about the best sort to buy for your garden sweet potatoes.

Meet the author: Mattias is an experienced gardener spending most of his free time on his knees among herbs, plants and garden vegetables. For the past two years he has been sharing gardening projects and how-to tutorials on the NordicLavender website and YouTube channel.