Sweetcorn
Zea mays
Wind-pollinated, which is the one fact that decides whether it works: sweetcorn must be planted in a block of short rows rather than a single long one, because pollen has to fall from the tassels onto the silks of neighbouring plants. A tidy single row produces cobs with a scatter of kernels and gaps between them.
- Position
- Full sun
- Water
- moderate demand
- Drainage
- Free-draining, Moisture-retentive
- Grows to
- 150–200 cm × 30–45 cm
- Hardiness
- H2
- Harvest
- August and September
- Difficulty
- Some care needed
Described view
A diagram contrasting sweetcorn planted in a four-by-four block with the same number of plants in a single row, showing pollen falling onto neighbouring silks in one case and blowing away in the other
August
Harvest
Sweetcorn’s year
Resolved for United Kingdom (general). Every window is stored against a climate event rather than a date, so a late frost pocket runs later than the band shows. What else August calls for.
| Activity | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow under cover | April. | May. | ||||||||||
| Plant out | May. | |||||||||||
| Harvest | August. | September. |
Timing that travels
The band above resolves this plant's windows into months for one region. These are the windows themselves, stored against a climate event rather than a date — which is the form that survives being carried to a colder garden, a frost pocket, or next year.
- Plant out1–3 weeks after your last spring frost
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — plant out
Checked 2026-08-13
In a block at least four plants by four, not a row.
Conditions it needs
- Light
- Full sun
- Frost
- Frost tender
- Hardiness rating
- H2 (RHS)
- Grows best at
- 18–30 °C
- Germinates at
- 13–30 °C
- Soil
- Loam, Sandy
- Soil pH
- 6–7
- Drainage
- Free-draining, Moisture-retentive
- Water needs
- moderate
- Drought
- moderate tolerance
- Waterlogging
- poor tolerance
- Heat
- good tolerance
- Wind and exposure
- poor tolerance
Where these figures come from
- LightSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — position
Checked 2026-08-13
- FrostSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — hardiness
Checked 2026-08-13
- Hardiness ratingSourced guidancemoderate confidence
- Royal Horticultural Society: RHS hardiness ratings
Checked 2026-08-13
- Grows best atSourced guidancemoderate confidence
- Royal Horticultural Society: Sweetcorn — temperature
Checked 2026-08-13
- Germinates atSourced guidancemoderate confidence
- Royal Horticultural Society: Seed germination temperatures
Checked 2026-08-13
- SoilSourced guidancemoderate confidence
- Royal Horticultural Society: Sweetcorn — soil
Checked 2026-08-13
- Soil pHSourced guidancemoderate confidence
- Plant Finder — Missouri Botanical Garden: Zea mays — culture
Checked 2026-08-13
- DrainageSourced guidancemoderate confidence
- Royal Horticultural Society: Sweetcorn — soil
Checked 2026-08-13
- Water needsHorticultural consensusmoderate confidence
Critical during flowering and cob filling; less so before.
No external citation — see the evidence type above.
Checked 2026-08-13
- DroughtHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- WaterloggingHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- HeatHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- Wind and exposureHorticultural consensusmoderate confidence
Tall and shallow-rooted; a summer gale flattens a block.
No external citation — see the evidence type above.
Checked 2026-08-13
On your soil
Computed by comparing this plant's recorded requirements against each soil's recorded characteristics. A recorded horticultural fact overrides the comparison where GrowingHQ holds one.
| Soil | Verdict | Why |
|---|---|---|
| Heavy clay | Works, with one condition | Sweetcorn will crop on heavy clay, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse. |
| Sandy | Prefers this soil | Sandy suits Sweetcorn as it stands: The pH suits it: it wants 6 to 7, and this soil is in that range. The free drainage is exactly what it wants. Sandy soil is among the soils it is recorded as suiting. |
| Chalky and alkaline | Works, with one condition | Sweetcorn will crop on chalky and alkaline, but one thing has to be dealt with first. The soil is substantially too alkaline for it: it wants pH 6 to 7, and this soil sits around 7.8 to 8.5.The pH is the obstacle. Small shifts are achievable and slow; large ones are not. On chalky and alkaline the dependable answer is a container of the right compost rather than an attempt to change the ground. |
| Loam | Prefers this soil | Loam suits Sweetcorn as it stands: The pH suits it: it wants 6 to 7, and this soil is in that range. The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. The soil holds moisture, which saves a great deal of watering. |
| Silty | Prefers this soil | Silty suits Sweetcorn as it stands: The pH suits it: it wants 6 to 7, and this soil is in that range. The free drainage is exactly what it wants. The soil holds moisture, which saves a great deal of watering. |
| Peaty and acid | Works, with one condition | Sweetcorn will crop on peaty and acid, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse. |
| Shallow over rock | Prefers this soil | Shallow over rock suits Sweetcorn as it stands: The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. |
| Made ground and urban soil | Works, with one condition | Sweetcorn will crop on made ground and urban soil, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse. |
Not sure which you have? Four hand tests will settle it.
Space and spacing
- Mature height
- 150–200 cm
- Mature spread
- 30–45 cm
- Rooting depth
- 45 cm
- Spacing
- 35–45 cm apart
Where these figures come from
- Mature heightHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- Mature spreadHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- Rooting depthHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
- SpacingSourced guidancemoderate confidence
- Royal Horticultural Society: Sweetcorn — spacing
Checked 2026-08-13
In a container
- Minimum volume
- 20 litres or more
Where the container figures come from
- Minimum volumeHorticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
Possible with several plants grouped closely so they can pollinate each other. A single plant in a pot produces nothing worth eating.
Where and how you can grow it
Each way of growing is assessed separately, and “not assessed” is a real answer rather than a gap we have filled in with a guess.
| Method | Suitability | What it needs |
|---|---|---|
| Open ground | Well suitedsourceSourced guidancemoderate confidence
Checked 2026-08-13 | |
| Traditional dug bed | Well suitedsourceSourced guidancemoderate confidence
Checked 2026-08-13 | |
| Raised bed | Well suitedsourceSourced guidancemoderate confidence
Checked 2026-08-13 | |
| Greenhouse | WorkablesourceSourced guidancemoderate confidence
Checked 2026-08-13 | |
| Polytunnel | WorkablesourceSourced guidancemoderate confidence
Checked 2026-08-13 | |
| Container | MarginalsourceSourced guidancemoderate confidence
Checked 2026-08-13 | 20 litres each, and several grouped together for pollination |
| Hydroponics | Not suitablesourceSourced guidancemoderate confidence
Checked 2026-08-13 | Far too large and too demanding of root volume. |
Growing it
- PlantingPlant in a block rather than a row — at least four by four. Sweetcorn is wind-pollinated, and pollen shed from the tassels has to land on the silks of nearby plants. A single row lets most of it blow away, and the cobs come out with gaps.
- WateringWater heavily from the point the tassels appear until the cobs fill. Before that sweetcorn is fairly drought-tolerant; during it, a dry fortnight produces cobs with shrivelled kernels at the tip.
- ProtectionAn annual, killed by frost, and not overwintered. Its autumn relevance is what happens to the stems: they are tough and slow to break down, so chop them up before composting or they will still be recognisable next summer. Clearing the stubble also removes overwintering sites for the moth larvae that occasionally tunnel into cobs.
Where this guidance comes from
- PlantingSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — planting
Checked 2026-08-13
- WateringSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — care
Checked 2026-08-13
- ProtectionSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — cultivation
Checked 2026-08-13
Is it worth putting under cover?
Whether it will grow there is on the methods table above. This is whether the space is well spent, which is a different question and usually the one being asked.
| Structure | What protection is worth | What decides it |
|---|---|---|
| Greenhouse | Extends the seasonsourceGrowingHQ editorial positionmoderate confidence What protection is worth for this crop, judged against the same standard as every other record in this file.
Checked 2026-08-13 | Pollination and height. Sweetcorn is wind-pollinated and two metres tall, so a still, low house gives blank cobs from plants pressed against the glass.Start it under cover, plant it out in a block. The block is what pollinates it. |
| Polytunnel | Extends the seasonsourceGrowingHQ editorial positionmoderate confidence What protection is worth for this crop, judged against the same standard as every other record in this file.
Checked 2026-08-13 | Pollination and height, slightly better in a tunnel because doors at both ends move air through the crop. |
Harvesting
- When it is readyThe silks turn brown and dry. Press a kernel with a thumbnail: milky sap means ready, clear watery sap means too early, doughy means too late. Cook it the same day — the sugars begin converting to starch within hours of picking.
- How to pick itHold the stem with one hand and pull the cob sharply downwards and twist with the other; it comes away cleanly. Pick and cook the same day if you possibly can — the sugars in sweetcorn begin converting to starch within hours of picking, and that, rather than anything about growing it, is why home-grown sweetcorn tastes different.
Where the harvest guidance comes from
- When it is readySourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — harvesting
Checked 2026-08-13
- How to pick itSourced guidancehigh confidence
- Royal Horticultural Society: Sweetcorn — harvesting
Checked 2026-08-13
What goes wrong
| Problem | How often | Notes |
|---|---|---|
| Slugs and snails | occasionalsourceHorticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13 |
What to look for
Views that settle something a description cannot. Where the photograph has not been taken yet, the description of what it will show is here instead — which is the useful half of it either way.
Described view
A sweetcorn cob peeled back at the correct stage with plump kernels, beside an under-ripe one with small pale kernels
- The thumbnail test: milky sap is ready, clear sap is too early.
Sources for this page
GrowingHQ editorial synthesis · Plant Finder · Royal Horticultural Society
Each figure on this page carries its own citation, under the “where these figures come from” note in its section. Record last reviewed 2026-08-14.