Sweet potatoes are colourful, tasty and lower in calories than traditional potatoes. Modern varieties are bred for the British climate to produce a worthwhile crop of uniform roots.
Which to choose
Beauregard is a trusted favorite variety for the UK climate. It’s compact and bears high yields of deep orange fleshed tubers that store very well. However a larger range is available such as Carolina Ruby Sweet Potato and many more varieties.
When they arrive
Unlike traditional potatoes, Sweet Potatoes are grown from unrooted or partially rooted cuttings known as ‘slips’ and plug plants. (The average length of a slip is 8in/20cm).
Slips can look alarmingly wilted on arrival but do NOT worry!!
Lay them in a shallow bowl of cool water approx. 2cm deep so that all of the stem is just covered with water. Placing in a warm light room. Leave them in this state for at least a week until the roots have started to form from the stems. Add fresh water daily in order to keep the slips healthy and stop the water from turning sour.
Arriving in a blister pack, open the blister pack on arrival and check contents. Each plant will already have a well developed root system and a stem and leaves up to 15cm in overall length. If dry lightly mist the root balls to moisten. Prepare to pot on in the next few days, keeping the root ball moist and in a warm light room.
Potting on Slips
Once the roots have developed, carefully plant the whole slip individually. Mostly fill a 9cm pot and lightly firm the compost before curling the stem around the pot and laying on the compost surface, topping with compost so that the stem is just covered leaving the base of the leaves protruding. Water and keep warm, +15 oC. Allow the plants to establish root systems within the pots before planting on into their final containers. This typically takes around 3 weeks.
Either plant directly into the heated poly tunnel, greenhouse or 30cm container or nurture in 9cm pot indoors until ready for final planting. Fill a 9cm pot with compost shake soil level with top of pot. Do not firm. With your finger make a hole large enough to take the root ball of the plug plant and push in the plant so that the root ball sits just below the surface. Shake the pot so compost levels, water and keep warm indoors. +15 oC
Choose the site
Sweet Potatoes require full sun and high temperatures and plenty of space to provide good yields. In the UK they are best planted in poly tunnels or greenhouses, however in a warm sheltered outdoor spot they can thrive. In order to increase productivity of the plants try covering the beds in black membrane and ‘planting through’ or planting in black 30cm containers or patio gro bags to increase soil temperature, Fleece and cloches can also help.
Prepare the soil
Prepare the soil in prior to planting in late May; make sure it is well drained and aerated. Good drainage is essential so plant in a raised bed if you garden on heavy soil. Not too much nitrogen required.
Plant the rooted plants 1ft/30cm apart, and leave at least 75cm between rows. Sweet potatoes are scrambling plants (members of the Ipomoea family) so give them space to grow.
For the best results and to develop maximum sweetness, grow in full sun.
Water regularly and feed weekly with a multipurpose fertiliser.
Tie in stems to trellis or strings if required.
Harvest and Store
Plants are ready to harvest 120 days after planting, expect to harvest the tubers in October once the leaves turn yellow and die back. The tubers can stay in the ground longer but harvest before the first frosts. Lift in the same way as potatoes and let the skins toughen by leaving them in the sun for a few hours, move to a bright humid place such as a greenhouse for a week or so, to help storage.
5 slips / plants should give at least 5kg -10kg of sweet potatoes depending on location. In the north expect to get 1-2kg of sweet potato tubers per slip, in the warmer south it should be in excess of 2kg per planted slip.
Store sweet potatoes somewhere cool once tubers are completely dry.