How to grow sweetcorn

Inspired by a helpful YouTube guide. This guide draws on the GrowVeg video "How to Grow the Best Corn!", which covers the key tips for getting reliable cobs in the UK climate — variety choice, the block-planting trick for pollination, and knowing exactly when to harvest. Well worth ten minutes before you start.

1. Choose a reliable UK variety

In the UK, warmth is the limiting factor. Pick an early or mid-season variety bred to ripen before the season ends. Varieties like Earlibird, Earligold, Swift, and Lark are reliable in the British climate. Avoid very late American varieties — they need a longer, hotter summer than we can reliably provide.

Supersweet (SH2) varieties stay sweeter for longer after harvest if that matters to you. Standard sweet varieties (SU) are more forgiving to grow but need eating quickly. Both are excellent when truly fresh.

2. Start indoors in mid-spring

Sow from mid-April into root trainers or 9cm pots on a warm windowsill. Sweetcorn dislikes root disturbance, so avoid sowing into modules that will require pricking out. One seed per pot, pushed in about 2.5cm deep. Germination happens in a week or so at 18–21°C.

Do not sow too early. Six-week-old transplants are about right for planting out. Older, rootbound plants do not establish well and often produce poorly.

3. Plant out in a square block, not rows

Sweetcorn is wind-pollinated. The male flowers at the top shed pollen onto the female silks lower down. If you plant in a single row, plants at the ends receive much less pollen and produce poorly filled cobs — the gaps where kernels should be are caused by failed pollination.

Plant in a square or rectangular block instead: at least four plants wide in each direction. Space them 45cm apart each way. Planted out after the last frost — typically late May to early June in Kent — they grow fast once warm weather arrives.

4. Water consistently at the roots

Sweetcorn is a thirsty crop, especially once tassels appear and cobs start to swell. A steady, deep watering at the base twice a week in dry weather is better than light, frequent splashing. Allow the soil to dry slightly between waterings — waterlogged roots cause problems.

Side-dress with a general-purpose fertiliser when plants are knee-height. A mulch of compost around the base helps retain moisture and suppress weeds, which compete hard with sweetcorn in summer.

5. Watch for the silks to brown

Cobs are ready when the silks (the wispy threads emerging from the top) have turned brown and dry. The cob itself should feel firm and well-filled when you squeeze it gently through the husk. To check, pull back a small section of husk and pierce a kernel with your thumbnail — a milky white liquid means it is perfectly ripe. Clear liquid means wait; no liquid and a doughy texture means it is past its best.

Timing matters. A few days either side of peak ripeness makes a noticeable difference to flavour.

6. Harvest and cook immediately

Twist the cob firmly downward from the stem. Cook it within the hour if you can, or at least the same day. Sweetness diminishes with every passing hour after harvest — this is not an exaggeration, it is basic plant chemistry.

Most plants produce two cobs. Harvest the upper one first; the lower one usually follows a week or so later. Once both are taken, the plant’s work is done and it can be composted.

When to call a handyman

Sweetcorn is a very DIY-friendly crop. That said, if you need help clearing a patch for a new vegetable garden, building raised beds, or putting up a windbreak to shelter taller crops, Richard is glad to help.