Unlike normal potatoes; sweet potatoes are grown from slips (the young stems growing from the tubers). They are at just the right size for you to continue the growth yourself. We can supply you with a bunch; every slip can be given a container each for lots of mature potatoes.
1) What to do when they arrive
Arriving as Slips
When they arrive to you, your slips may have wilted; THEY DO REVIVE. We recommend you place them in a vase of flask of water immersing the slips right up to the leaves.
Leave for 24 hours in a cool and dry place- not on a windowsill above a radiator or a sill that receives full sun. An east or west-facing windowsill is perfect.
Arriving as Plug Plants
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.
2) Potting on
Once your slips have revived it’s time to put them into pots to grow on under cover until it’s warm enough to grow them outdoors.
- Fill pots will multi-purpose compost and plant up to leaf height.
- Planting one slip per pot
- Keep your pots overnight in temperatures no lower than 13°C (55°F). We recommend a cool porch or unheated room.
- During the day, keep in a light but airy position.
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 and 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 (+15C).
3) Where to plant sweet potatoes
Sweet Potatoes require full sun, high temperatures and plenty of space to provide good yields. In the UK they are best planted in poly tunnels or greenhouses, however, they can thrive outdoors if they have moisture retentive free draining soil and are in a warm, sheltered outdoor spot with plenty of sun. To try and increase the productivity of the plants try covering the beds in black membrane and ‘planting through’ or planting in black 30cm containers to increase soil temperature. Fleece and cloches can also help.
4) Preparing the soil for planting
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 is required.
5) Planting sweet potatoes
Keep an eye out for the roots. By no means do they want to be curling around the side of the pot; curling roots lead to deformed tubers.
- Before planting them out in the open, harden them off for a week, gradually increasing their time outside.
- Plant them from slips into large Gro bags or a 30-40cm (12-16in) diameter pot, they can also be planted into soil but should be spaced 30 cm (12in) apart and rows should be 80cm (32in) apart.
- Plant them in full sun three to four weeks after the last frost when the soil has warmed.
- Bury them to the same level as they are in the pots, press the soil down gently but firmly, then water well.
- If the weather is dry provide 1 inch of water a week until two weeks before they are due to be harvested. Letting the soil dry out.
- The sweet potatoes will be ready around four months later. The leaves will have yellowed and start to die back which indicates harvest-time.
6) 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, as they will rot quickly. 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.
What is the expected yield from sweet potatoes?
If you were to plant 5 slips/plants the expected yield should be at least 5kg -10kg of sweet potatoes depending on location. In the north, you should 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.
Common problems of sweet potatoes
When grown, in the UK, sweet potatoes suffer from very few problems. However, if you find that the tubers are smaller than expected this is probably caused by lack of warmth. They also don't like being waterlogged, this can cause the tubers to rot. To avoid this, ensure the ground is well drained.
If you are growing them in a greenhouse or polytunnel, whitefly can be a problem. To avoid this spray with an appropriate insecticide.