The sweet potato is not actually a true potato, it is a semi tropical plant that grows best between 20°-30°C (68°-86°F) and is propagated vegetatively from cuttings called slips.
As a result of this, they can only be grown successfully outdoors in the milder areas of the UK, in cooler areas, they should be grown in a cool glasshouse or polytunnel.
Sweet Potato tubers
They require deep well drained sandy loams with a pH of 6 to 7.
In shallow soil it is advantageous to grow them on ridges of soil.
Heavy soils should be avoided where possible.
Moisture content of the soil is critical to get good results.
They like moist but not waterlogged soil, and they should never be allowed to go dry.
Sweet potatoes require less fertiliser than most vegetables.
Soil fertilised for a previous vegetable crop should suffice.
Keep the growing area free of weeds although once the plants cover the ground, the crop tends to smother further weed growth.
They are relatively free of pest and disease problems.
Good rotation and hand weeding will minimise the need for pesticides.
However in cold wet soils fusarium could cause root rot.
Circa week 10:
Lay tubers lengthways on a tray then half cover them with damp sand.
Place the tray on a hotbed to promote sprouting.
This procedure will encourage slips to grow.
When they (the slips) are 100-125mm (4"-5") long break them off and pot them them into 1 litre pots of compost.
Circa Week 20:
Once all risk of frost has passed, plant them out in the greenhouse or tunnel bed.
Plant them out 300mm (12") apart in rows 1 metre (39") apart.
Sweet Potatoes are members of the ipomea family, and as such the top growth spreads quite rapidly, so quite a bit of space is needed.
They should be ready for croppng within 15-16 weeks.
Pot the mail order slips immediately on receipt into individual pots of multipurpose compost.
The slips should be well watered before potting up and then kept in humid propagator to encourage rooting.
If no propagator is available cover the pots with a clear plastic bag and keep in a warm spot.
Once rooted gradually harden off the plants in a frost-free, well-lit spot until planting out time.
Plant out rooted slips with 50-75mm (2"-3") of tip exposed.
It is best to plant the cuttings at an angle of 45° and 300mm (12") apart in rows 1 metre (39") apart.
Circa Week 34-35:
When the haulms start to yellow harvesting can begin.
Harvest and handle the potatoes with extreme care to avoid bruising which can cause storage problems.
Do not wash roots intended for storage.
After lifting, store the potatoes in a humid location at a temperature of around 15°-20°C(60°-70°F) for a couple of weeks to cure the skins, this will increase their keeping quality and flavour.