How to Grow Sweetcorn

Sweetcorn is a warm-season crop that thrives in sunny, sheltered locations. It’s easy to grow if your soil is fertile and you start it at the right time. Sweetcorn is wind-pollinated, so it should be grown in blocks, not single rows, to ensure good kernel set.

You can grow:

• Traditional tall varieties (Incredible F1, Swift, Lark F1)

• Mini corn (picked before fertilisation)

• Super-sweet varieties (Mirai, Supersweet 100)

🗓️ Month-by-Month Growing Guide (UK)

January

🧤 Plan & Prepare

• Choose your varieties and check if you want early, maincrop, or supersweet types.

• Sweetcorn needs sun, warmth, and fertile soil — choose a sheltered plot away from strong winds.

• Dig the bed and add well-rotted manure or compost.

• Clean and organise pots or trays for spring sowing.

February

🌱 Soil Preparation

• Rake and cover the bed with black plastic to warm the soil.

• Collect peat-free compost and 9 cm pots for sowing in spring.

• Make sure the area gets full sun for most of the day.

March

🌾 Early Sowing Under Cover (Optional)

• In a heated greenhouse or propagator (around 18–21°C), sow seeds individually in 9 cm pots.

• Push seeds 2–3 cm deep, pointed end down.

• Keep moist but not soggy.

• Label varieties and keep trays in bright light.

April

🌿 Main Sowing Time (Indoors or Under Cover)

• Sow main batches indoors now — sweetcorn dislikes root disturbance, so start in deep pots or modules.

• Germination takes 7–10 days.

• Turn plants daily so they grow straight.

• Prepare outdoor beds with compost and rake level.

• If weather is mild late in the month, you can sow directly outdoors under fleece.

May

☀️ Harden Off & Plant Out

• Harden off indoor-grown plants for 7–10 days before planting out.

• Once frost danger has passed (mid- to late May), plant in blocks, not rows:

  • Space 35–40 cm apart each way.

• Water well after planting and mulch around the base.

• Stake if the site is exposed.

June

🌾 Steady Growth

• Keep beds weed-free and water regularly, especially in dry spells.

• Feed fortnightly with liquid seaweed or a balanced fertiliser.

• Hill up soil gently around the base to anchor roots.

• As tassels appear (the male flowers on top), shake the stems on calm days to help pollination.

July

🌽 Flowering & Pollination

• Silks (female flowers) appear halfway up the plants — this is where the cobs form.

• Continue watering well; drought now can ruin your harvest.

• Feed weekly with tomato feed or high-potash fertiliser.

• Remove side shoots if plants are crowded, but this is optional.

August

🌞 Cobs Swelling & Ripening

• Keep watering steadily until kernels form fully.

• To test ripeness: peel back a little husk and press a kernel — if milky juice appears, it’s ready.

• Harvest promptly — sugars convert to starch quickly after picking.

• Pick regularly to encourage remaining cobs to mature.

September

🍂 Harvest & Clear

• Finish harvesting before frost.

• Pull up plants and chop them for composting (or stack for wildlife habitats).

• Clear beds and dig in compost or manure to prepare for winter crops.

October

🌾 Soil Care

• Spread a thick layer of compost or manure over the old sweetcorn bed.

• Cover with black plastic or cardboard to protect over winter.

• Review which varieties performed best for next year.

November–December

❄️ Rest & Plan

• Clean tools and trays.

• Order next year’s seeds early for the best varieties.

• Rotate your crops — avoid planting sweetcorn in the same spot next season.

🌼 Key Growing Tips

• Sun: Full sun, sheltered from wind.

• Soil: Fertile, well-drained, moisture-retentive.

• Watering: Deeply during dry weather, especially at flowering.

• Spacing: 35–40 cm apart in square blocks.

• Feeding: Liquid feed every 2 weeks once plants reach knee height.

• Harvest: 16–20 weeks after sowing (usually August–September).

• Storage: Best eaten fresh — harvest just before cooking for maximum sweetness.

🌤 Tip of the Season

“Plant sweetcorn in blocks, not rows — they pollinate by wind, and this ensures plump, golden cobs.”