Vegetable · Poaceae
Sweet Corn
Zea mays
Plant it in a block, not a row, feed it well, and sweet corn rewards you with full, milky ears by late summer.
Full sun
Every 3–7 days
50–95°F · 10–35°C
60–100 days
Overview
Sweet corn is a tall grass grown for the sugary ears it makes in high summer. It traces back to the Americas, where people bred it from wild grasses thousands of years ago, and it now grows as a warm season annual in gardens almost everywhere. Give it sun, warmth, and rich ground, and a few square feet can hand you a real summer crop.
The one thing corn asks that most vegetables don't is company. It pollinates on the wind, with pollen falling from the tassels at the top onto the silks below, so a lone row or a single plant sets badly. Plant it in a block of several short rows and the wind does the work, filling every ear from butt to tip.
Corn is a hungry plant. It needs steady water and a heavy hand with nitrogen, and it runs short on patience for cold soil and crowding. Get the timing and the feeding right and it grows fast, but cut corners and you trade full cobs for gappy, half-filled ears.
Care
The short version: full sun, rich soil, and plenty of water, planted in a block rather than a single row so the wind can pollinate it. Feed it well, since corn is a heavy nitrogen feeder, and keep it moist once the silks appear.
Light
Corn wants full sun, the more the better, with no shade to speak of. Tall and fast-growing, it shades itself enough already, so give it the open, sunniest spot you have.
Water
Keep the soil evenly moist, working out to about an inch of water a week. Moisture matters most from tasseling and silking through ear fill, when a dry spell leaves you with poorly filled ears.
Soil
Plant in fertile, well drained loam with plenty of organic matter dug in. A pH of 6.0 to 6.8 suits it best, and rich ground feeds the heavy appetite corn brings.
Temperature
Corn grows across a wide band, from about 50°F to 95°F (10°C to 35°C), but it needs warm soil to start and a long warm stretch to ripen. Cold ground rots the seed before it sprouts.
Humidity
Ordinary outdoor humidity is all it needs, so there's no number to track. What matters more is the wind, which carries the pollen from tassel to silk and fills out the ears.
Feeding
Corn is a heavy nitrogen feeder. Work a balanced fertilizer in at planting, then side-dress with nitrogen once the plants reach about a foot tall and again when they tassel.
Pruning
There's nothing to prune. Leave the tillers that sprout at the base of the stalks, since taking them off doesn't raise yield and can lower it. Cut out only smut galls or clearly diseased stalks.
Size & spacing
Stalks stand 5 to 8 feet (150 to 250 cm) tall and take up little width, so set plants close, about 8 to 12 inches (20 to 30 cm) apart. Pack them into a block of several short rows rather than one long line.
When to plant
Corn lives and dies by warmth and has no tolerance for frost. Wait until the cold has passed and the soil has warmed to at least 60°F (16°C), then sow the seed straight in the ground. Plant a fresh patch every couple of weeks and you'll be picking ears from midsummer into early fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Not recommended; corn resents root disturbance and is best direct-sown
- Plant: Direct sow after the last frost once soil has warmed to at least 60°F (16°C); plant in blocks of at least 3-4 short rows rather than one long row to ensure wind pollination
- Harvest: Tassels and silks appear in mid to late summer; harvest at the milk stage, about 18-24 days after silks appear, when kernels exude milky juice when punctured and silks are brown and dry
Hardiness
USDA hardiness zones: 2–11
Temperature: down to -46°C
Troubleshooting
Most corn trouble shows up on the ears or the stalks, and a lot of it traces back to how the plant was set out rather than to any pest. Catch the early signs and you can save the crop or at least the cobs already on the plant. Match what you see below, then act while it still helps.
Caterpillars and chewed kernels at the tip of the ear
This is the corn earworm, a caterpillar that rides down the silk channel and feeds at the top of the ear. The damage usually stays in the first few inches, so cut the tip away and the rest of the cob is fine. A few drops of mineral oil on the silks a few days after they appear, or a spray of Bt, keeps the next ones out.
Fix:
- Cut away the damaged tip; the rest of the ear is fine to eat
- Apply a few drops of mineral oil to silks 3-7 days after silking begins
- Treat fresh silks with Bt (Bacillus thuringiensis) or spinosad according to label directions
Gappy ears with missing or shriveled kernels
Skipped kernels mean poor pollination, almost always from planting in a single row where the wind can't carry pollen to every silk. Drought during silking makes it worse. Plant in a block of at least three or four short rows next time, keep the soil moist once the tassels show, and shake the tassels over the silks by hand to fill in a small patch.
Fix:
- Water deeply during silking and ear fill
- Hand-pollinate small plantings by shaking tassels over fresh silks
Swollen gray galls that burst into black powder
These growths are common smut, a fungus that slips in through wounds and runs in hot, dry weather, especially where nitrogen is heavy. The galls start firm and silvery, then darken and split to spill powdery black spores. Cut them out and bin them before they rupture, and never add them to the compost.
Fix:
- Remove and destroy galls before they rupture; do not compost them
Stalks toppling over or snapping in the wind
Corn topples for two reasons, so check the base before you blame the weather. Shallow roots in loose soil give way in a storm, while small entry holes ringed with sawdust-like frass mean a corn borer has tunneled the stalk from inside. Stand the plants back up and hill soil around the base, then shred and till in the old stalks at season's end to clear out the borers that overwinter there.
Fix:
- Gently stand plants back up and hill soil around the base after storms
- Destroy crop residue after harvest to remove overwintering borers
Rusty orange spots or long tan streaks on the leaves
Powdery orange spots that rub off on your fingers are common rust, while long cigar-shaped gray-tan lesions point to northern corn leaf blight in warm, humid spells. Late in the season neither does much real harm and can be left alone. Strip off the worst lower leaves, and plant resistant hybrids next year to stay ahead of it.
Fix:
- Remove heavily infected lower leaves
- Severe cases on young plants may warrant a labeled fungicide; late-season infection rarely needs treatment
Toxicity
Good news here: sweet corn is safe. No part of the plant is poisonous to people, pets, or livestock, which is why it shows up on dinner plates and in animal feed alike. The one thing to watch is the bare cob, which a dog can swallow and choke on or block its gut, so keep finished cobs out of reach.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
No poison here. A cat that nibbles a leaf or a stray kernel is in no danger from the plant itself.
Dogs None
The plant won't poison a dog, but the cob is a real hazard of a different kind. A swallowed cob or chunk of one can lodge in the gut and block it, so keep whole cobs well out of reach.
Horses Safe
Grain corn is a common feed, and the plant holds nothing toxic for a horse.
Rabbits Safe
Safe to browse, though a rabbit does best on leafy greens with only a little corn now and then.
Livestock Safe
Corn has fed cattle, sheep, and goats for generations and carries no toxin for them.
Birds Safe
Hens and wild birds eat the kernels happily, and there's nothing in the plant to harm them.
People Safe
Sweet corn is a kitchen staple, eaten fresh off the cob or cooked, with no part of it off limits.
Although corn is not poisonous, whole corn cobs are a serious physical hazard for dogs: swallowed cobs or cob chunks commonly cause choking or intestinal obstruction. Never give dogs cobs to chew and secure compost and trash.
Varieties
Sweet corn comes in standard, sugary-enhanced, and supersweet types, each holding its sugar a little differently after picking. These are a few worth knowing by name.
Silver Queen
A classic standard white variety grown for its flavor, ripening in roughly 88 to 92 days.
Bodacious
A sugary-enhanced yellow type with tender, sweet kernels that come in around 75 days.
Ambrosia
A sugary-enhanced bicolor of yellow and white kernels, also about 75 days, and a favorite in home gardens.
How Sweet It Is
A supersweet white that holds its sugar longest after picking, but needs warm soil and must be kept apart from other corn types.
Companions
Corn grows best with the partners that share its bed in the old Three Sisters planting, and worst beside crops that feed the same pests it does.
Plant near
Pole beans: Traditional Three Sisters partner; beans fix nitrogen that benefits this heavy-feeding crop and use cornstalks as a living trellis
Squash: Traditional Three Sisters partner; broad squash leaves shade the soil, conserving moisture and suppressing weeds around corn
Keep apart
Tomatoes: Corn earworm and tomato fruitworm are the same insect (Helicoverpa zea), so adjacent plantings build shared pest pressure
How to propagate
Corn is grown one way, from seed sown right where it will stand, since it hates having its roots disturbed.
SeedEasy
Direct sow after the last frost when soil is at least 60°F (16°C); make succession sowings every 2-3 weeks for a continuous harvest · Seeds germinate in about 4-10 days in warm soil
Corn is grown straight from seed, sown right where it will grow, because it transplants poorly. Plant the seeds 1 to 1.5 inches deep and 8 to 12 inches apart in blocks of at least three or four rows so the wind can pollinate them, and they break ground in about 4 to 10 days once the soil is warm. Sow a fresh patch every 2 to 3 weeks to keep ears coming, and keep any supersweet variety well away from other types, since cross-pollination turns the kernels starchy.
Myths
Pulling off the side shoots at the base of the stalk gives you more corn.
Those base shoots, called tillers or suckers, do no harm if you leave them. Removing them does nothing for yield and the open wounds can stress the plant or let disease in, so leave the tillers alone.
A single long row of corn fills out fine as long as the plants look healthy.
Corn rides the wind for pollination, and every silk needs a grain of pollen to set a kernel. One row catches too little and you end up with gappy ears, so plant in blocks of at least three or four short rows instead.