Fruiting vegetable (cereal)
How to grow sweetcorn
Zea mays
Sweetcorn needs warmth, a sheltered spot in full sun and company. Sow indoors in deep pots from mid April to mid May and plant out in early June, after the last frost, in a block at least four plants by four. The block matters because sweetcorn is pollinated by wind, and plants in a single row give cobs with half the kernels missing. Square raised beds suit this well, because you plant them as a block anyway. Choose an early variety, feed with nitrogen and water well once the silks appear.
- Hardiness
- Tender
- Position
- Full sun, sheltered
- Soil
- Rich, moisture-retentive, free-draining
- Ideal pH
- 6.0 to 7.0
- Water
- Moderate to high, critical at tasselling and cob fill
- Feeding
- Heavy feeder
Sowing and planting sweetcorn
WhenSow Apr to May indoors (or late May direct); plant out Jun in blocks; harvest Aug to Oct
Starting off
Sow indoors mid April to May, one seed 2.5 cm deep in a 9 cm pot or deep root-trainer at 18 to 21 °C, germinating in 7 to 10 days; plant out in early June after hardening off, before the roots spiral. Direct sow in late May under cloches once the soil is above 10 °C. Isolate supersweet types from others by 8 m.
Spacing and planting
Plant 35 to 45 cm apart each way in a block of at least 12 to 16 plants, 4 rows by 4, never a single row, so wind carries pollen. Sow or plant 2.5 cm deep and earth up 10 cm around the stem in July. Not a container plant, though 4 plants in a 50 litre tub will set a few cobs.
Varieties worth growing
- Swift F1
- Early, tender and very sweet, with good vigour in cool soil. The most dependable choice for the Midlands and north.
- Lark F1
- Mid-season, with thin-skinned, very sweet kernels and well-filled cobs; germinates better in cool conditions than most sweet types.
- Sundance F1
- Early, traditional sugary type that sets reliably in a poor summer. Less sweet than modern hybrids, but needs no isolation from them.
- Earlibird F1
- Early supersweet with long cobs. Keep it apart from other types, or the kernels turn starchy.
- Minipop F1
- Grown for baby corn, picked unpollinated when the silks first show, so it can be planted 20 cm apart and needs no block.
Sweetcorn month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do.
- February
Nothing to do. Order seed.
- March
Spread compost on the bed and fork it in.
- April
Sow indoors from mid month, one seed per 9 cm pot or deep cell, at 18 to 21 °C.
- May
Last indoor sowing by mid month. Harden off. Sow direct under cloches late in the month.
- June
Plant out in a block in the first half of the month. Fleece on cold nights.
- July
Nitrogen top-dress at knee height. Earth up the stems. Water in dry weather.
- August
Water heavily while silks are showing and cobs fill. Test early varieties when the silks turn brown.
- September
Main harvest. Pick and cook the same day.
- October
Last cobs early in the month. Clear the plants; chop the stalks before composting.
- November
Nothing to do.
- December
Nothing to do.
Feeding sweetcorn
A tall grass with a grass's appetite for nitrogen. That makes the best fertiliser for sweet corn one that leads with nitrogen, backed by a soil rich in compost. Feed the bed before planting and top-dress once at knee height; after the tassels appear, water matters more than feed.
Hungry, especially for nitrogen, feed well and keep watered at tasselling and as the cobs fill.
Feeding plan
March or April
Garden compost
One 10 litre bucket per square metre forked into the top 20 cm.
Late May, a week before planting
Fruit & Vegetable Fertiliser 4-5-6
100 g/m² raked in. At 45 cm each way a plant has 0.2 m², so that is 20 g per plant, or about 320 g for a block of 16.
At planting, once
5 g per litre of root-ball volume. The root ball from a 9 cm pot is about 0.4 litres, so 2 g per plant, dusted into the planting hole where it touches the roots.
Early to mid July, when plants are knee high, once
Organic Nitrogen Fertiliser 13% N
40 g/m², the top of the label range for leafy crops: 8 g per plant, or about 130 g (three to four rounded handfuls) spread over a block of 16, then watered in.
At planting, tubs
Fruit & Vegetable Fertiliser 4-5-6
5 g per litre of compost mixed through: 250 g for a 50 litre tub. Top-dress with 2 g per litre (100 g) at knee height.
Signs to watch
Pale, yellow-green leaves and thin stems at knee height
Nitrogen short on a hungry crop
Nitrogen top-dress now
Purpling leaves and stems in a cold June
Phosphorus locked up by cold, not short
Fleece and wait
Cobs with patchy, missing kernels
Poor pollination in a single row or drought at silking
Plant in blocks and water at tasselling
Pests, diseases and problems
Seed sown outdoors or in a cold frame disappears, leaving small holes
Mice, which dig up and eat the seed
Raise plants indoors in pots, out of reach, and plant out at 15 cm tall.
Young plants shredded or pulled out; later, husks torn open and kernels pecked
Woodpigeons, jackdaws and rooks
Net or fleece the block for three weeks after planting. For ripening cobs, slip a paper bag or a cut-off plastic bottle over each one.
Stems flattened or snapped and ripe cobs stripped overnight in August
Badgers, squirrels or rats, which take the cobs just as they ripen
Only a sturdy barrier works: wire mesh fencing pegged or buried at the base. Pick the moment cobs are ripe and do not leave any standing.
Large, pale grey swellings on cobs or tassels that burst into black powder
Sweetcorn smut, a fungus seen in hot, dry summers
Cut off the galls before they burst and bin them; do not compost. Clear all plant debris after harvest and grow sweetcorn elsewhere for the next few years.
Young plants with a dead central shoot, or twisted, ragged leaves and stunted growth
Frit fly larvae feeding in the growing point in May and June
Raise plants in pots and plant out at the five or six leaf stage, when they are past the vulnerable period; cover direct sowings with fleece or fine mesh.
Young plants grazed at the base, with ragged strips eaten from the leaves
Slugs and snails
Plant out sturdy pot-raised plants, not small seedlings, and apply slug nematodes to moist soil at planting.
Harvest and rotation
Harvest and storage
Ready August to September when the silks have turned brown and a pierced kernel runs milky, 14 to 18 weeks from sowing; clear sap means wait, doughy means over-ripe. Hold the stem and twist the cob downward. Each plant gives 1 to 2 cobs. Sugar turns to starch within hours, so cook at once, or blanch and freeze the day they are picked.
Rotation and companions
Rotation: a grass, so it fits anywhere and is a useful break in a 4-year cycle; follows legumes well for their nitrogen. Climbing French beans up the stems and squash at the base make the 'three sisters', the squash shading out weeds.
Good to knowPlant in a block, not a single row, so the wind can pollinate it; harvest when a squeezed kernel runs milky.
Growing sweetcorn in pots
Sweetcorn can be grown in containers, but treat it as an experiment and do not expect a full crop. Pollination needs several plants close together, so one plant per pot gives little. Use the largest tub you have, at least 50 litres, and set four plants in a square about 25 cm apart, or stand three or four such tubs together to make a block. Choose an early variety such as Swift. The tub will need watering daily from July, and twice a day in a hot spell when the cobs are filling. When the tassels open, tap the stems at midday to shake pollen down on to the silks. Expect one cob per plant.
Sweetcorn: common questions
Should I remove the side shoots from sweetcorn?
No, leave them. The side shoots, called tillers, that grow from the base do no harm, and their leaves help feed the plant. Removing them wounds the stem and has not been shown to improve the crop. Earth up over the roots that form at the stem base instead, for stability.
Can you grow different varieties of sweetcorn together?
Not if one of them is a supersweet. When a supersweet variety is cross-pollinated by another type of sweetcorn, the kernels turn tough and starchy. Grow one variety per season, or keep different types at least 8 m apart, or choose varieties that flower weeks apart.
Can you sow sweetcorn directly outside in the UK?
Yes, from late May, once the soil is above 10 °C, but pot-raised plants are more reliable. Sow two seeds per station 2.5 cm deep under a cloche or cut-off bottle and thin to the stronger. Direct-sown plants ripen two or three weeks later, so use an early variety.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.