Growing sweet potatoes (Ipomoea batatas) is easy but getting the amount of crops you expect from them might get a little tricky, especially when attempting to grow them in containers. While regular potatoes might thrive in buckets or grow bags, sweet potatoes require perfect conditions to thrive.
I’ve tried many times to grow sweet potatoes in containers and, until this year, failed miserably. Understanding the plant and its natural habits is the best place to start with new crops, including how to adapt the growing habits of sweet potatoes to small spaces if necessary.
Anyway, here is our guide to sweet potato container gardening, and a few experiments I’ll be trying this year based on the natural habits of sweet potatoes.
The natural habits of sweet potatoes
To grow anything, you have to understand the plant’s natural habit, and sweet potatoes, in particular, are fussy plants, but you can create the perfect conditions by growing sweet potatoes in containers.
Firstly, it’s important to establish the difference between sweet potatoes (Ipomoea batatas) and your regular potatoes (Solanum tuberosum). I don’t usually refer to plants’ Latin names, but in this case, it gives us huge clues about how to grow them – and more importantly how to control them.
Potatoes are part of the nightshade family, the same as tomatoes, so are subject to blight, with poisonous leaves (if you’ve ever spent the day pruning tomatoes and found a rash all over your arms, you’ll know where I’m coming from). Solanum tubers will also grow in tightly packed spaces.
Ipomoea, the family whose most famous members are Sweet Potato and Morning Glory, are trailing or climbing plants, with high disease tolerance, but low frost tolerance. Most importantly, sweet potatoes are tropical plants. They require heat, humidity, space, and lots of organic matter, and unlike potatoes, they are best prepared as slips – I’ll explain that process later.
The best varieties for sweet potato container gardening
Sweet Potato Makatea is the most widely accepted container variety, but from experience, it is more of a shower than a grower. Makatea is brilliant for a patio display and will provide a decent crop too, but Tahiti is a less vigorous vine producer, seeming to focus its energy to the root where it matters.
Have a go with Sweet Potato Tahiti for easy to manage, reliable crops or try Erato Orange for the classic tubers, which I will personally vouch for following my first decent crop of sweet potatoes this year.
Growing sweet potatoes vertically
The growing habits of sweet potatoes are often misunderstood because when we grow them, we tend to grow them vertically. However, in nature, they sprawl across the ground and each plant can cover 2m2 in a year.
Sweet potato’s nature as a trailing plant also means any stems in contact with the soil will try to root. This takes the sugars from photosynthesis away from any tubers you’re nurturing. So, keeping the foliage up off the ground isn’t just space-saving, it’s actually beneficial to your crops.
Whatever the size of your garden, you don’t want to give a single plant that much space, so how do you train sweet potatoes?
Unlike their close cousin, Morning Glory, sweet potatoes do not send out functional tendrils despite having the same distinct Convolvulus flowers and leaves, so they cannot climb without help.
To grow sweet potatoes in a container you are best training them manually up a 6-8ft trellis, wire frame, or tepee, and tying in regularly with soft twine.
The other benefit of vertical growth is that sweet potatoes have edible leaves, often spoiled by soil splatter if trailing on the ground. Their leaves can be used like spinach, either fresh in salads, or steamed, wilted or sautéed. Darker leaves have a high Vitamin C content, but all leaves have a distinct bitter note similar to chicory, which adds sharpness to your greens and pairs well with a clove of crushed garlic, vinegar, and honey. Which is, conveniently, a lovely side dish for baked sweet potato.
What pots to use for sweet potatoes
Sweet potatoes need space. They will naturally root from any part of the stem with soil contact, which takes energy away from crops, so give them space, but raise them up.
Use the basic rule of one plant every 2ft. Your average 30cm pot is fine for one slip, but bigger is better. This year we grew ours in raised beds, but it’s better advised to grow in pots, so you can move them around the garden – especially for hardening off young plants in spring.
If you have thick-walled pots, wooden planters, or terracotta pots, these are better for sweet potatoes. Reusing large black plastic pots helps heat up the roots on warm days too. The most important thing is keeping every part of the plant as warm as possible. They can be grown in potato bags, but they will be more susceptible to temperature changes so it is not advised.
Size matters though, and sometimes that means cutting a few corners to save money. A plastic storage box (ideally at least 2ftx2ft) lined with newspaper to stop light reaching the roots, will do the job – or if you’re not planning on moving it, an allotment neighbor of mine once successfully grew sweet potatoes in an old cardboard box. By the end of the year, the box had disintegrated, but the crops were incredible; the heat from the decomposing cardboard kept the root system warmer than cool plastics.
Remember, you can plant sweet potatoes in any kind of container, as long as it’s well insulated and big enough to allow for at least 5 new tubers per plant – anything less and you’ll end up with lots of small, slightly bitter roots, which aren’t worth eating.
Soil conditions for sweet potatoes in containers
The basics: use moisture retentive, free-draining soil and add lots of organic matter mixed with loamy topsoil if you have it.
As long as you have good drainage and plenty of organic matter, sweet potatoes will grow beautifully but there are a few tricks to help move things along faster.
Add a layer of fresh manure to the bottom of the pot and cover with a small layer of straw. On top of that add whatever compost is best for your plant. For sweet potatoes, a mix of basic peat-free compost and leaf mold is perfect. What you’re creating is a mini hotbed, where the manure rots down underneath the straw, creating constant heat throughout the growing season.
Positioning sweet potatoes in the garden
The reason tropical plants grow so well as houseplants is because day length isn’t really that important. They need around 4-6 hours of sun, but it’s the heat of our homes that really helps them out. Sweet potatoes are the same. If you can give them heat, they will grow almost anywhere in the garden.
If you have a warm wall (either south-facing or underneath a boiler outlet) it can really boost their growth. Ours were grown on a generally shaded north-facing wall this year, but the heat from the boiler kept them warm enough to yield a generous crop.
Wind doesn’t directly affect growth, and won’t cause damage to the plants, but the chill can be fatal if it’s constant, so try to keep your plants out of the path of regular breezes.
Sweet potato slips
What is a sweet potato slip? It’s pretty simple really, and if you’ve ever taken young cuttings from a dahlia, you’ll already be familiar with the process.
A sweet potato slip is a long young shoot that will grow from the sweet potato itself once it has been given water or a growing medium. The slip can have early signs of roots at its base, but even if you start without roots, once they are removed from the potato tuber and placed in water, roots will soon appear, quickly followed by foliage.
How to prepare sweet potato slips:
- Slice a sweet potato in half width ways, and leave it cut side down in water (change the water every few days and preferably only use rainwater or filtered water as sweet potatoes are very sensitive to the chlorine in our tap water).
- The tuber can send out roots, but it’s the green shoots that appear that we’ll be keeping, these are your slips! It can take around a month until the slip (shoot) is 8-10 inches long with true leaves.
- Break the shoot off the tuber, being careful not to damage roots at the base of the shoot. Discard or compost the tuber.
- Place all shoots in rainwater for one week until they have their own roots.
- Pot them up with a basic peat free cutting compost in individual 9cm pots.
- Leave them indoors or in a greenhouse/cold frame for another month once you’ve potted the plants, away from any danger of frost.
- That’s your slips sorted.
When to prepare sweet potato slips:
Sweet potato slips can be started in early winter, or even late autumn. I’m experimenting with mine in early November this year, partly because it might give me a head start in the cold North, but also because they make amazing houseplants until you take them outside.
What works without fail is starting your slips in late January. You won’t get to enjoy the indoor foliage as much, but you’ll have a reliable crop. Start sweet potato slips in January indoors or late February in a greenhouse or cold frame.
When and how to transplant them to the garden:
Remember, sweet potatoes are from warmer climates. They need heat to crop, and their foliage and flowers are easily killed by frost.
When all risk of frost has passed, pot your slips into their final positions (it doesn’t matter if you bury them a little, as long as some leaf is still showing – they will root from the stem). Then move your sweet potato plants outside for a few hours every day for a week to harden them off.
Do this from early April in warmer regions or mid-May in colder climates. The best measure is when nighttime temperatures are consistently above 10C.
Harvesting sweet potatoes
Harvesting times for sweet potatoes depend on a few factors, but the signs are always the same.
When the sweet potato leaf tops start to yellow in late summer/autumn, they’re ready for harvest. This means September or October for most temperate climates. Leaving it any later runs the risk of frost damage which won’t ruin your crop, but will shorten its storage time.
When the leaves begin to turn yellow at their tips, trace the plant back to its crown at the base.
Because you’re growing in pots there is no need to risk stabbing a fork through your harvest, simply cut back all the top growth, and if there is anything green left, keep it for salads or stir-fries, then tip out the entire pot.
You should have around 1lb of sweet potatoes per plant (5-10 tubers).
- Cure them on a sunny windowsill or in the greenhouse for 1-2 weeks.
- Then store and eat!