Sweet potatoes will grow however you tell them to, as long as you understand their basic nature, and growing sweet potatoes in raised beds is a great place to start if you have the space to spare.
Our guide to sweet potato container gardening has all the steps on getting started, whatever sized space you’re working with. Since I garden in a colder climate, growing sweet potatoes is particularly challenging, but not impossible – you can read through the basics of growing them in the UK here.
For growing sweet potatoes in raised beds, you have one big choice to make: do you let them grow naturally along the ground, or train them up? The answer depends on where you are.
If you’re growing them somewhere with short winters, and warm springs, growing them along the ground will give you a perennial crop that needs very little attention. If you’re anywhere else then you need to grow sweet potatoes vertically.
Preparing raised beds for sweet potatoes
How big do the raised beds need to be?
Ideally, you want to keep to garden or allotment regimented so it’s easier to manage, so dedicating one bed to sweet potatoes is recommended. Because they are best grown vertically, consider growing them in rows so you can have a single supporting structure for each row.
The ideal raised bed needs to be at least 1ft deep, and 1 ft wide. The length depends on how many sweet potatoes you want to plant per row, but one tuber per 1ft will work nicely.
On our plot this year, we’ve built a new bed, 3ft x 8ft bed, so we can have two rows per bed that can be easily managed from either side next year.
Alternatively, grow them along the back of a bed so other crops can grow in front of them. Companion planting with sweet potatoes is tricky, but if you have space left in the raised bed, consider planting herbs next to your sweet potato crop, including Summer savory (Satureja hortensis), which will deter the threat of the dreaded sweet potato weevil.
How deep should the raised beds be for growing sweet potatoes?
Sweet potatoes can grow up to 30cm deep but typically go around 15-20cm in depth. If they hit a block at the base of the bed they will grow fatter rather than longer, so it’s not a big issue. But it’s definitely worth making your beds as deep as possible to prevent straining the sweet potato plant.
Vertical growth or trailing?
I would always advise vertical growth, even if you have the right climate for trailing sweet potatoes. That way you can fit more crops in a small space and get higher yields.
The sweet potato tubers grow downwards into the soil from the crown of the plant, and if you harvest them gently they will be connected by a single main root. Tubers won’t extend too far out in the soil, but the sweet potato plant will produce massive top growth.
Building a frame out of bamboo or bean poles and running twine from that frame down to each plant is a great setup. You’ll have plenty of material to tie vines to, and it lets you keep an eye on the base of the plant too.
- Tip: Prepare your trellises beforehand as sweet potatoes are vines that grow quickly. This expandable trellis is a sturdy option for sweet potatoes, but you can also use it with peas, cucumbers and even squash.
Pollination doesn’t matter for sweet potatoes, so grow them in grids, rows, or individual spots. Also, consider deadheading the flowers regularly to keep energy passing down to the roots.
Soil conditions for sweet potatoes in raised beds
The same rules of sweet potato container gardening apply to growing sweet potatoes in raised beds. They need plenty of organic material and good drainage to thrive.
Leave enough space in your raised beds for a healthy layer of fresh manure, then straw or newspaper. The soil or compost mix on top of that is the growing medium.
If you’re using an existing raised bed and are practicing no-dig, start the process in early winter by mulching heavily with fresh or part rotted manure, which will impart its goodness on your beds in time for planting next year.
Improving soil conditions for sweet potatoes
If you plan on planting sweet potatoes in an existing bed, you need to make sure the soil is right in advance. Sweet potatoes prefer slightly acidic soil and hate chlorine. Apart from that, a basic garden compost and leaf mold should be added to the surface.
- Tip: You can check the acidity of your soil using a pH meter.
If you’re not sure about acidity in your soil, add a sprinkling of fresh pine needs to the surface, and scrape off once they turn brown. This will gently raise the pH levels to something they can cope with, but it isn’t usually necessary.
The main challenge when planting into an existing bed is making sure it’s in full sun, shaded from wind, and that you only put sweet potatoes in their final positions in early summer.
If you can’t guarantee warmth in spring, there is a risk of losing your plant entirely, and while the tubers can recover from a surprise frost, they might not manage to produce new growth in time for cropping the same year.
The hot bed method for sweet potatoes
By far the best way of growing sweet potatoes in a cold climate is the hot bed method. Sweet potatoes thrive in hot conditions, and as long as the drainage is properly prepared you’ll have an incredible crop.
Anyone with an allotment will be familiar with the principle, as there is always one show-off growing a pumpkin on a pile of manure or rotting compost.
The heat caused by decomposition and the millions of microorganisms in the pile can create steam even in deep winter, which means you can start crops earlier, and end them later.
This year we tried a miniature version of this, with a lasagne of manure, straw, and compost in a large pot and it worked wonders, so we’ve started building a larger model in the greenhouse. We’ll be trying sweet potatoes using that setup this year.
To build your own, all you need are two pallets cut in half
- Attach the pallets in any shape you like, making sure it is at least 2ft tall
- Line the inside with scrap timber, or anything you have lying around
- Fill 1/3 up with manure
- Cover with straw (this keeps the oxygen in for decomposition)
- Cover with 1/3 compost (or a compost and top soil mix as long as it is free draining)
- Cover with glass or Perspex to keep the heat in. Or build the entire thing in a greenhouse
The following year, the contents of this mini hot bed can be used to mulch other beds in winter, so nothing goes to waste.
So there you go, you’ve just learned the basics of growing sweet potatoes in a temperate climate inside raised beds:
- Make sure your beds are deep enough – 1ft or 30cm is best.
- Space your sweet potato tubers at least 1ft apart, or create narrow beds that are 1 ft wide.
- Avoid allowing your sweet potato vines to trail on the ground – raise them up on the structures of your choice.
- Fill your beds with plenty of organic material and cover them with mulch.
- On pre-existing raised beds, add semi-rotted manure in winter.
- Make sure the beds of your choice receive plenty of sunlight in spring, summer and autumn.
- Only plant your sweet potato slips once the danger of frost has passed.
- Try out the hot bed method of growing sweet potatoes for best results.
Growing a tropical plant in a temperate climate is always a thing of trial and error, but if you’re up to the challenge, it’s well worth it. Sweet potatoes store very well and they’ll make an excellent crop to last you through that hungry gap.