Sweet Potato

Sweet potato (Ipomoea batatas) is a trailing herbaceous plant in the morning glory family, producing large, starchy, sweet-tasting tuberous roots in a range of flesh and skin colours from white to deep orange and purple. It is a heat-demanding crop that requires a long, warm growing period to produce a good harvest. Young shoots and leaves are also edible as greens. In Nordic conditions it must be started indoors well in advance and grown under the warmest possible conditions.

Growing

Start slips or tubers indoors once indoor temperatures stay reliably above 21 °C — place tubers half-submerged in water or lay them on moist compost to sprout. Once slips reach 15–20 cm and have several leaves, pot them on individually. Transplant outdoors only when soil temperature reaches at least 18 °C and nights stay consistently above 15 °C. Plant slips 5 cm deep and space 35 cm apart in rows 60–75 cm apart. Choose the warmest, most sheltered spot available — raised beds or dark plastic mulch to warm the soil are strongly recommended in Nordic gardens.

Care

Water consistently during establishment, then reduce frequency but keep soil evenly moist — never waterlogged. Apply a low-nitrogen, high-potassium and phosphorus fertiliser every three to four weeks to encourage tuber development rather than leafy growth. Vines spread aggressively; redirect rather than prune them to maintain photosynthetic capacity. Remove any flowers to direct energy to the roots. Black plastic or fleece mulch retains warmth and suppresses weeds, which is critical in short, cool growing seasons.

Harvest

Harvest when foliage begins to yellow and die back, or when tubers feel firm and skins resist light scratching with a fingernail. Carefully dig with a fork, working at least 30 cm away from the crown to avoid slicing the tubers. Harvest the entire planting before soil temperatures drop below 15 °C, as cold soil damages the skins and shortens storage life. Handle gently — bruises lead to rot.

In the kitchen

Roast whole at high heat until caramelised, or cube and steam, boil, or mash. The natural sweetness pairs with warming spices such as ginger, cinnamon, and chilli. Slice thin and bake into crisps, purée into soups, or incorporate into gratins and curries. Young leaves can be stir-fried or added to soups much like spinach.

Storing

Cure freshly harvested tubers at 28–30 °C with high humidity for 7–10 days to heal skin damage and convert starches to sugars. After curing, store in a dry, well-ventilated location at 13–16 °C — avoid refrigeration, which causes chilling injury and off-flavours. Properly cured tubers keep for 3–6 months. Do not store near apples or other ethylene-producing fruits.