Sweet Corn
Corn, Maize, Sweetcorn
Plant in blocks (4+ rows) not single rows for proper wind pollination. Direct sow after last frost 1" deep, 9–12" apart. Needs consistent moisture especially during tasseling/silking. Pick 18–24 days after silk appears, when silk browns. Use immediately after harvest — sugars convert to starch rapidly.
- Germination
- 7–10 days
- Soil temperature
- 16–29 °C
- Harvest after sowing
- 65–90 days
- Spacing
- 25–30 cm
When to plant sweet corn
Sow outdoors from your last spring frost to 2 weeks after it.
Dashed line: typical last spring frost in zone 7 (Apr 5). Zone dates are averages; most of the UK is zone 8–9, central Europe 6–7 and the Baltics and Scandinavia 4–6. In the app, Tomatograph uses your garden's own frost dates.
How to grow sweet corn
- 1
Sow in blocks
Sow 2.5–4 cm deep and 23–30 cm apart after the last frost, once soil is above 16 °C. Plant in a block of at least four short rows, not one long row, so wind can pollinate every ear.
- 2
Water at tasselling
Keep water steady, and especially generous when tassels and silks appear: dry soil then leaves gaps in the cobs.
- 3
Keep apart
Grow sweet corn away from popcorn or field corn, which can cross-pollinate it and reduce sweetness. Sow another block every 2–3 weeks for a longer harvest.
- 4
Harvest
About 18–24 days after silks appear, when they are brown and dry. A kernel pressed with a fingernail should give milky juice. Eat or chill straight away; sugar turns to starch within hours.
Growing conditions
Light
Full sun
Water
High water
Temperature
10–35 °C
Frost tolerance
Frost-sensitive — protect below 0 °C
Days to maturity
80 days
Plant spacing
30 cm
Ideal soil pH
5.5–7.5
How Tomatograph watches your sweet corn
Tomatograph checks your local forecast every morning and only speaks up when one of these applies to your garden.
- Forecast of 2 °C or lowerFrost alert the evening before: cover plants with fleece or bring pots inside.
- 3 days at 35 °C or aboveHeat-wave alert while plants are flowering or fruiting: shade and water early.
- Humidity above 80% for 48 hoursCheck for smut, which thrives in those conditions.
- Under 5 mm of rain forecast over 3 daysWatering reminder: water deeply at the base, early in the morning.
- Within a week of maturityHarvest-window reminder based on when you planted.
Sweet Corn questions
- When should I plant sweet corn?
- Sow outdoors from your last spring frost to 2 weeks after it.
- How long do sweet corn seeds take to germinate?
- Usually 7–10 days at a soil temperature of 16–29 °C.
- How long until I can harvest sweet corn?
- About 65–90 days after sowing, depending on variety and weather.
- How far apart should I plant sweet corn?
- Allow 25–30 cm between plants.
- What grows well with sweet corn?
- Good neighbours include green bean, squash, cucumber, pea.
Growing guide written by Tomatograph. Planting figures from openplantdb (CC0 1.0). Zone frost dates are averages from openplantdb (CC0 1.0).