GardenCalcs.uk
Sweetcorn Block Calculator — Wind Pollination Layout
Plan sweetcorn block planting for proper wind pollination.
Minimum 3, ideally 4+
Minimum 3, ideally 4+
RHS: 34-45 cm in every direction across the block; use 60 cm for vigorous tall varieties
Cost per seed (a packet of ~50 F1 seeds is often £2-4, so roughly 4-8p each); leave at 0 to hide cost
Extra seeds to sow for germination failures (default 1.5 = 50% extra)
Average cobs per plant for yield estimate (default 1.5)
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.
Frequently Asked Questions
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.
45cm between plants in all directions is standard. Some vigorous varieties need 60cm. Never plant in a single row.
Most varieties produce 1-2 cobs per plant. Supersweet varieties tend to produce fewer but sweeter cobs.
Sow indoors in April (one seed per pot) or direct sow in late May after the last frost. Sweetcorn needs warm soil to germinate.
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.
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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.