Sweet potatoes are a delicious, nutritious crop, and with the use of a polytunnel, it is well suited to any garden. Packing a powerful punch of flavour, nutrients and vitamins, they can be used in a variety of sweet and savoury dishes. Boasting a similar texture and versatility to common white potatoes, sweet potatoes have a delicately sweet flavour that makes them ideal for use in curries, stews and sweet treats, as well as being turned into healthy chips and crisps. Their leaves are also delicious when treated like spinach or added to soups and salads.
While sweet potato crops have traditionally been cultivated in warmer climates, more and more people are choosing to utilise polytunnels in order to grow this delicious root vegetable. Hardier varieties are also making waves, meaning that gardeners around the UK can harvest sweet potatoes.
While sweet and white might both share the name “potato,” they are not actually related! The sweet potato is related to the morning glory family, while white potatoes belongs to the nightshade genus. Sweet potatoes are also much more nutritionally sound than their namesake, as they are packed with iron, calcium, selenium, Vitamin C and many B vitamins, as well as beta carotene.
Best of all? Sweet potatoes count towards your ‘five a day,’ while white potatoes do not. Great news! You can dig into some oven baked sweet potato chips without any guilt.
Polytunnels can help to protect delicate seedlings and crops from more inclement weather, insects and animal pests. By creating a warmer environment, a polytunnel can behave similarly to a small greenhouse, allowing traditionally warm climate fruits and vegetables to thrive in the UK.
Unlike many other fruits and vegetables, sweet potatoes are not grown from seeds. Instead, they are grown from ‘slips.’ Slips are clippings that have been taken from mature sweet potato plants, and you can order them online or through mail order catalogues.
When you start looking around for your slips, it is important that you choose them from a company that sells hardy varieties that are suited to the UK. If you plant tropical variants, they will not survive in our cooler weather and shorter growing seasons.
The slips will thrive best if you plant them in sandy soil that is reasonably warm and drains freely. Your garden’s soil doesn’t match this description? You might have a lot more success if you plant the slips in raised beds or large containers, and place them in the sunniest part of your polytunnel. It is also a good idea to warm your polytunnel’s soil with back polythene before you plant the slips. You can also increase the soil temperature with cloches or horticultural fleece.
Sweet potatoes typically have a long growing season, so you will want to plant your slips as early in the season as possible. Cover the soil in late March or April, and get the slips in the ground as soon as you notice the temperatures rising (usually late May or early June). While you might be eager and tempted to plant your slips, don’t put them in the soil too early. Instead, keep them on a sunny windowsill in your home until they are 6 to 12 inches tall.
You will have the best success with your sweet potatoes if they are at a temperature of 21-26 degrees Celsius. While the South of the UK usually reaches these temperatures in the summer (and then some), some areas in the North might need to take additional warming measures.
Plant your slips 12 to 18 inches apart, to a depth of approximately 8 to 10 inches, and then mound the soil to 8 inches tall and 12 wide. They should be deep enough to cover the roots and an inch or so of the stem.
Sweet potatoes appreciate a lot of water, and it is a good idea to feed them with a high potassium feed every two weeks or so.
As soon as you see that your sweet potatoes are big enough to cook with, you can start harvesting them (this is usually 3 to 4 months – i.e. 100 days - after you plant the slips). Another way you can tell that they are ready to harvest is when the leaves start to yellow, but don’t worry – you can leave them in the ground until the first frost.
You might want to use a spade fork for the harvesting process, because the roots spread about 6 inches. You can feel free to cut some of the vines away, and then pull up the crown carefully so that you do not bruise the sweet potato. Shake away the dirt, but don’t wash them, as water can hasten rot.
It is always a good idea to cure your sweet potatoes to increase their sweetness. This allows them to develop a second skin over any scratches that occurred when you unearthed then. In order to cure them, store them in a warm environment at high humidity (80°F/27°C and about 90%) for between 10 to 14 days. You can then store them in newspaper in a cool, dry place for approximately 6 months.
late May/early June
after at least 100 days, and before first frost
Now that you can see just how simple polytunnels can make growing sweet potatoes in the UK, maybe it is time to give this crop a go? After all, there are very few other vegetables that are as versatile and nutritious, and so a steady supply is always nice to have on hand! Vitamins, minerals, tasty flavour and a great texture – what’s not to love?