Plant
- Late spring
buy slips or plug plants, pot them immediately and establish them somewhere warm and bright.
Sweet Potatoes
This Allotment Pro editorial draft summarises the cited RHS guide. Check the source and adjust timings for local conditions.RHS source guide
Month by month
Plant out
- Late spring to early summer
harden off strong rooted plants and move them to a greenhouse, coldframe, protected container or exceptionally warm outdoor site after frost danger has passed.
Harvest
- Early autumn
lift the tubers after four to five months, before the first frost.
1 - Getting Started
Sweet potatoes, Ipomoea batatas, are tender tropical climbing or trailing plants grown for their edible storage roots. They are relatives of morning glory and only distantly related to traditional potatoes. In the UK they are normally grown as annual vegetables from cuttings called slips or from rooted plug plants, not by planting whole tubers as seed potatoes.
Heat determines success. Plants crop best at 21–26°C (70–80°F), with full sun and regular watering, so a greenhouse is the most dependable position. They can grow in greenhouse soil, large tubs or grow bags. Outdoor crops are worthwhile only in very warm sheltered sites and benefit from cloches or plastic-free fleece in all but the most favourable areas.
The vigorous stems trail or climb for 1.5m (5ft) or more. Let them sprawl where space allows, or train them vertically to save ground. Young shoots and leaves are also edible and can be cooked like spinach, although removing too much growth reduces the root harvest.
2 - Choosing What To Grow
Sweet-potato cultivars differ in root size, shape, skin and flesh colour. Orange, purple, red and white forms are available, and some have decorative purple-tinted foliage. Most need at least four to five months of warmth, so choose cultivars offered for UK conditions. Beauregard is among the hardier choices for outdoor growing.
Slips and rooted plugs are generally sold by online vegetable-plant suppliers from late April, with young plants sometimes available in garden centres.
Recommended varieties
Beauregard
Sweet and tasty salmon-orange flesh, with growth suited to the UK climate.
Bonita
Pale tan skin and orange flesh, reaching harvest about 100 days after slips are planted.
Evangeline
A very vigorous, especially sweet cultivar that needs a long hot summer and performs best in a greenhouse.
Tahiti
Purple-skinned roots with white flesh, accompanied by attractive edible leaves.
3 - Planting
Establishing slips and plug plants
Unrooted slips and rooted plugs need warmth, bright light and consistently moist compost. Pot them immediately into small containers of peat-free multi-purpose compost. Slips may instead be stood in water until roots form, then potted. Place new plants in a propagator or beneath a clear bag to retain humidity until they grow strongly, and move them into slightly larger pots as required. Use tepid water.
To produce slips from a sound stored root, place it in moist sand in a warm propagator or airing cupboard in spring. When leafy shoots reach 5–7.5cm (2–3in), cut them cleanly from the base, insert them into small pots of peat-free multi-purpose or cuttings compost, and return them to a propagator to root.
Planting in the final position
Move well-rooted vigorous plants in late spring or early summer. Harden them off first if they will leave protected conditions. A greenhouse or coldframe gives the most dependable warmth; otherwise use a very warm, sunny, sheltered outdoor site and retain cloche or plastic-free fleece protection where possible.
For containers, choose a pot at least 30cm (1ft) wide and place one plant centrally at its former depth in peat-free multi-purpose compost. Water thoroughly. A grow bag is another option.
For ground planting, use moisture-retentive but free-draining soil. Incorporate about two bucketfuls of garden compost or well-rotted manure per square metre or square yard, or plant through an established no-dig mulch. Pre-warm outdoor soil beneath covers for several weeks. Set plants at their previous depth and at least 30cm (1ft) apart, firm gently and water generously.
4 - Plant Care
Sweet potatoes grow quickly when warm and may either sprawl or climb. Maintain dependable moisture throughout the long growing season so the storage roots can swell.
Watering
Keep soil or container compost consistently moist. Containers and plants in hot weather may need daily watering. Drought restricts root swelling. Water early or late in the day and use collected rainwater where possible. A pot sunk beside each ground-grown plant can direct water down to the root zone beneath dense foliage.
Mulching, feeding and weeding
Mulch ground-grown plants thickly with well-rotted manure or garden compost to hold moisture and suppress weeds. Well-prepared ground needs no routine feed. Feed container plants every 14 days through summer with a high-potassium organic liquid fertiliser. Weed young plants carefully; established vines usually shade much of the soil.
Supporting plants
Where ground space is short, use a wigwam of canes about 1.8m (6ft) high. Containers can stand beside a sunny wall or fence with wires or trellis. In a greenhouse, train stems up canes or strings suspended from the roof.
5 - Pruning And Training
Routine pruning is unnecessary. Trim only stems that escape their allotted space, and cook young removed shoots and leaves as a leafy vegetable if desired. When growing vertically, tie selected stems to their supports until they climb securely. Heavy leaf harvesting reduces the root crop, so treat shoots as a secondary harvest.
6 - Harvesting
Lift roots after four to five months when foliage yellows and dies back in early autumn, always before frost. Tip a container out gently or use a garden fork around ground-grown plants. The skin is delicate, so avoid bruising or cutting the roots and use damaged ones immediately.
Warmth, moisture and growing-season length determine yield and root size. Dry sound tubers in warm sunshine for a few days to improve their skin before storage. Even cured roots generally keep only a few weeks under home conditions, so lift one or two plants at a time where frost risk permits and inspect stored roots frequently for deterioration or rot.
7 - Problem Solving
Sweet potatoes are normally vigorous and healthy, but insufficient heat or moisture can prevent a useful crop. In the UK a greenhouse and regular watering provide the most reliable conditions. Protected plants may attract sap-feeding mites and whiteflies.
Common problems
Glasshouse red spider mite
These tiny sap feeders can mottle foliage and cause early leaf loss, especially in warm dry protected conditions. Inspect leaf undersides and act promptly while populations are small.
Problem sourceGlasshouse whitefly
Whiteflies feed on greenhouse plants and excrete sticky honeydew. Check new plants, inspect beneath leaves and use non-chemical prevention and biological controls where appropriate.
Problem source