Sweetcorn wants warm soil and a block, not a row

Sweetcorn needs warmth from start to finish. Sow it indoors from late March to late April and plant out in May, or sow outdoors from early May to mid-June. Then plant it in a block, not a row, or you’ll get cobs with gaps where the kernels should be.

It’s one of the most rewarding crops for a UK garden. Sweetcorn picked and cooked within the hour is far sweeter than anything you can buy.

Indoors or outdoors

Indoors gives the most reliable crop in most of the UK. Sow one seed per 8 cm pot or deep module, 2.5 cm deep, from late March to late April, and keep them somewhere warm. Root trainers are ideal, as sweetcorn dislikes root disturbance.

Outdoors works from early May in the south, once the soil has warmed. Sow two seeds at each spot and remove the weaker one. Cover with a cloche or fleece for the first few weeks.

Planting out

Sweetcorn is killed by frost. Plant out from early to late May, after hardening off for a week. These dates are for a typical lowland garden in England or Wales, with a last frost around 20 April. In Scotland, the north and frost pockets, wait until late May or early June, and choose an early variety.

Why a block

Each kernel on a cob is a separate flower with its own silk. Pollen falls from the tassels at the top of the plants and has to land on every silk. The wind does the work, and in a single row much of it blows away.

Plant in a block, with at least four rows of four plants, and pollen drifts onto silks from every direction.

1. Space plants 45 cm apart each way, or four to a square in square foot gardening.
2. Plant a little deeper than they were in the pot, and firm them in well against wind.
3. Water well after planting.

Runner beans, French beans, squash, courgettes and melons all grow happily with sweetcorn. Keep it away from tomatoes.

Care

Sweetcorn grows to about 1.8 m. Water well when the tassels appear and while the cobs swell, especially in dry spells, as dry plants give small, poorly filled cobs. A mulch helps.

Draw a little soil up around the base of the stems in summer to steady them against wind. The roots that grow from the lower stem will help too.

Avoid planting supersweet varieties next to other types, as cross-pollination can make both less sweet. Seed packets say which group a variety belongs to.

Picking

Sweetcorn is ready from mid-July to late October, about 70 to 100 days after sowing. Each plant usually gives one or two cobs, and a block crops over about three weeks.

Watch the silks. When they turn brown and dry, peel back a little husk and press a kernel. Milky juice means it’s ready. Twist the cob down and off the stem, and cook it quickly, as the sugar starts turning to starch as soon as it’s picked.

Common problems

Gappy cobs. Poor pollination. Plant in a block next time.

Seeds not coming up. Cold soil. Start them indoors or wait until mid-May to sow outside.

Mice and birds. They take seed and young shoots. Start plants in pots, or net the bed.

Badgers. In some gardens they flatten the crop just as it ripens. Strong fencing is the only reliable fix.

Set your own frost dates on the sweetcorn page, or see how sweetcorn fits with beans and squash in our companion planting guide.