Why must sweetcorn be grown in blocks?

Sweetcorn is wind-pollinated. Growing in blocks (at least 4x4) ensures pollen from the tassels reaches the silks on nearby plants for full cob development. A single row leaves most silks unpollinated, so cobs end up patchy and poorly filled.

What spacing should I use for sweetcorn?

45cm between plants in all directions is standard. Some vigorous varieties need 60cm. Never plant in a single row.

How many cobs per plant?

Most varieties produce 1-2 cobs per plant. Supersweet varieties tend to produce fewer but sweeter cobs.

When should I sow sweetcorn?

Sow indoors in April (one seed per pot) or direct sow in late May after the last frost. Sweetcorn needs warm soil to germinate.

Can I grow different sweetcorn varieties next to each other?

Keep supersweet (sh2) varieties away from standard and other types. The RHS warns that cross-pollination between varieties reduces the sugar content of supersweet cobs, so grow a single variety per block or separate varieties by distance or staggered sowing dates so they tassel at different times.

GardenCalcs

Sweetcorn Block Calculator — Wind Pollination Layout

Plan sweetcorn block planting for proper wind pollination.

Number of Rows

Minimum 3, ideally 4+

Plants per Row

Minimum 3, ideally 4+

Spacing

RHS: 34-45 cm in every direction across the block; use 60 cm for vigorous tall varieties

Price per seed (optional)

Cost per seed (a packet of ~50 F1 seeds is often £2-4, so roughly 4-8p each); leave at 0 to hide cost

How We Calculate This

Total plants = Rows x Plants per row. Block dimensions are calculated from spacing in all directions.

Seed count includes 50% extra (the default 1.5x over-sow factor) to cover germination failures and thinning. The RHS advises sowing two or three seeds at each station and thinning to the strongest seedling; if you sow that way, raise the over-sow factor to 2.0 or 3.0 in advanced options.

Yield estimate assumes 1.5 cobs per plant on average, which is typical for UK-grown sweetcorn.

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.