How to Grow Sweetcorn
Zea mays
When to Start
Start seeds indoors 4 weeks before your last frost date. Transplant outdoors once night temperatures stay above 10°C and soil has warmed to at least 10°C.
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Growth Stages
Approximate days from start
Care Essentials
- Nitrogen-rich feed at planting. Liquid feed when tassels appear.
- Wind-pollinated — plant in blocks, not rows, for good pollination. Supersweet types need isolation from other varieties.
Companion Planting
6 companion planting runner-beans, broad-beans, cucumber
Growing Conditions
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- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 45 cm |
| Row spacing | 45 cm |
| Sow depth | 3 cm |
| Mature height | 200 cm |
| Mature spread | 50 cm |
Crucially, must be planted in a block (e.g., 4x4 plants) rather than a single long row to ensure good wind pollination.
Companion Planting
Grows well with
In the classic Three Sisters system, runner beans use the corn stalk as a living trellis while their root nodule bacteria fix nitrogen that feeds the corn's high nutrient demand. Plant beans at the base of established corn plants (knee-high) so the corn has a head start before the beans begin climbing.
▼Broad beans fix atmospheric nitrogen through Rhizobium root nodules, gradually releasing ammonium that sweetcorn — one of the most nitrogen-hungry crops — draws on throughout its growth. Sow broad beans in autumn or early spring so they're already nodulating when corn goes in.
▼Sweetcorn stalks act as a natural windbreak and partial shade provider for cucumber plants, reducing the moisture stress that accelerates cucumber bitterness. Cucumbers planted on the east side of a corn row receive morning sun and afternoon shelter — the ideal microclimate for fruit production.
▼Garden peas fix nitrogen via Rhizobium root nodules and release it into the soil as they senesce, providing a natural nitrogen top-up for sweetcorn planted in the same or following season. Peas also mature earlier than corn, so they can be sown first and their dying foliage acts as a green mulch.
▼In the Three Sisters system, pumpkin's large prickly leaves carpet the ground between corn plants, suppressing weeds and locking in soil moisture while its rough texture deters raccoons and squirrels from reaching the corn. Space corn plants 45 cm apart to leave room for pumpkin runners to spread without crowding.
▼Courgette plays the same ground-covering Three Sisters role as pumpkin on a smaller scale — its broad leaves shade out weeds and retain soil moisture between corn plants. Courgette's more compact habit makes it easier to manage in smaller beds, and its flowers attract pollinators that also visit the corn silk.
▼Keep away from
Sweetcorn and tomato share the same primary pest — the corn earworm moth (Helicoverpa zea) lays eggs on corn silk and the larvae then migrate to tomato fruit, effectively doubling the infestation. Keep them at least 10 m apart, or use a physical barrier crop of tall sunflowers between them.
▼Care Guide
- Feeding
- Nitrogen-rich feed at planting. Liquid feed when tassels appear.
- Watch for
-
- Mice and birds (eat seeds)
- Smut
- Frit fly
Pests & Diseases
Pest Mice and Birds
Identification: Seeds disappear from drills; seedlings pulled up or nipped off at ground level; disturbed soil around sowing positions
- Cover newly sown areas with fine mesh or chicken wire until plants are well established
- Start seeds in modules indoors and plant out as sturdy transplants
- Use bird scarers or reflective tape near young plants
Pest Frit Fly
Identification: Central shoot (growing point) yellows and dies; stunted, distorted growth; small white maggots found inside stems when split open
- Sow later (late May/June) when frit fly activity has passed
- Start plants in modules indoors and plant out as larger, more resilient transplants
- Cover young plants with fleece
- No effective chemical treatments available to home gardeners; cultural controls are the main approach
Pest Slugs and Snails
Identification: Seedlings eaten at ground level; ragged holes in young leaves; slime trails around plants
- Apply organic slug pellets (ferric phosphate based) around newly planted seedlings
- Hand-pick at dusk; use beer traps
- Protect individual plants with cut plastic bottles as cloches
- Apply ferric phosphate slug pellets around vulnerable plants
Disease Common Smut Ustilago maydis
Symptoms: Large, grey-white galls on ears, tassels, stems, or leaves that burst to release masses of dark, powdery spores
Treatment: Remove and destroy galls before they burst and release spores; do not compost
Prevention: Rotate crops; avoid mechanical damage to plants; maintain even watering; remove affected plants promptly
Disease Northern Leaf Blight Exserohilum turcicum
Symptoms: Long, elliptical, grey-green lesions on leaves that turn tan as they mature; lower leaves affected first; severe cases reduce cob fill
Treatment: Remove badly affected lower leaves; improve air circulation
Prevention: Rotate crops; choose resistant varieties; ensure good spacing for airflow; clear crop debris at end of season
Growing Conditions
| Min. soil temperature | 10°C |
| Germination temperature | 15–25°C |
| Base growth temperature | 10°C |
| Min. daylength to start | 10h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Sweetcorn?
- Plant Sweetcorn 45cm apart with 45cm between rows.
- When can I harvest Sweetcorn?
- Sweetcorn is ready to harvest approximately 75 days after transplanting.
- What grows well with Sweetcorn?
- Sweetcorn grows well with runner beans, broad beans, cucumber.
- Is Sweetcorn frost hardy?
- Sweetcorn is classified as Tender.
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