Vegetable · Poaceae
Sweet Corn
Zea mays
Grow it in blocks, never a single row, keep it well fed, and sweet corn hands back plump, milky ears come late summer.
Full sun
Every 3–7 days
50–95°F · 10–35°C
60–100 days
Overview
Sweet corn is a tall grass that shoots up fast and hands you sugary ears at the peak of summer. It came out of 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. Hand it sun, warmth, and rich ground, and even a few square feet can deliver a serious summer crop.
Corn asks for one thing most vegetables skip, and that is company. It pollinates on the wind, with pollen showering from the tassels up top onto the silks below, so a lone row or single plant comes up short. Plant it in a block of several short rows and the wind goes to work, packing every ear from butt to tip.
Corn eats like it grows, fast and hungry. It craves steady water and a big helping of nitrogen, and it has no patience for cold soil or crowding. Nail the timing and the feeding and it rockets up, but cut corners and you swap full cobs for gappy, half-filled ears.
Care
The short version: give corn full sun, rich soil, and plenty of water, and plant it 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 craves full sun, the more the better, with no shade in the way. Tall and quick to climb, it shades itself plenty already, so hand it the most open, sun-drenched spot in the garden.
Water
Keep the soil evenly moist, aiming for about an inch of water a week. Moisture counts most from tasseling and silking through ear fill, since a dry spell right then leaves you with poorly filled ears.
Soil
Dig in loads of organic matter and plant into fertile, well drained loam. A pH of 6.0 to 6.8 hits the mark, and that rich ground fuels the big appetite corn shows up with.
Temperature
Corn powers along across a wide band, from about 50°F to 95°F (10°C to 35°C), but it needs warm soil to launch and a long warm stretch to ripen. Sow into cold ground and the seed just rots before it can sprout.
Humidity
Plain outdoor humidity is all corn wants, so skip chasing a number. The real player is the wind, which sweeps pollen from tassel to silk and packs out the ears.
Feeding
Corn is a heavy nitrogen feeder, so feed it big. Work a balanced fertilizer in at planting, then side-dress with nitrogen once the plants hit about a foot tall and again when they tassel.
Pruning
There's nothing to prune, which keeps things easy. Leave the tillers that sprout at the base of the stalks, since pulling them off won't boost yield and can drop it. Cut out only smut galls or clearly diseased stalks.
Size & spacing
Stalks rocket to 5 to 8 feet (150 to 250 cm) tall while staying narrow, so pack plants close, about 8 to 12 inches (20 to 30 cm) apart. Group them in a block of several short rows rather than one long line.
When to plant
Corn runs on warmth and folds at the first frost, so timing is everything. Wait out the cold, let the soil climb to at least 60°F (16°C), then sow the seed straight into the ground. Slip in a fresh patch every couple of weeks and you'll be hauling in 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 pops up on the ears or the stalks, and a surprising amount of it goes back to how the plant was set out rather than to any pest. Spot the early signs and you can rescue the crop, or at least the cobs already on the plant. Find the match below, then jump on it while it still pays off.
A caterpillar chewing kernels right at the ear tip
That caterpillar chewing the kernels up top is the corn earworm, which rides the silk channel straight down to feed at the tip. Don't write off the cob, though, because the damage seldom reaches past the first few inches; trim the tip and the rest eats beautifully. Get ahead of the next round by dropping a little mineral oil on the silks a few days after they show, or hitting fresh silks with a Bt spray.
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
Patchy ears riddled with holes and shrunken kernels
Gappy, shriveled kernels trace right back to poor pollination, almost always from a single row the wind just can't carry pollen across to every silk. Throw in a dry spell during silking and it gets worse fast. Turn it around next season: plant a tight block of three or four short rows, keep the soil moist the moment tassels appear, and shake the tassels over the silks by hand to fill in any thin patch.
Fix:
- Water deeply during silking and ear fill
- Hand-pollinate small plantings by shaking tassels over fresh silks
Fat gray galls bursting into a cloud of black powder
Those puffy growths are common smut, a fungus that slips in through wounds and races through hot, dry weather, especially when nitrogen runs high. They start firm and silvery, then darken and split wide to fling powdery black spores around. Move fast: cut them out and bag them for the trash before they burst, and never let them anywhere near the compost.
Fix:
- Remove and destroy galls before they rupture; do not compost them
Stalks going down or breaking in a strong wind
Before you blame the storm, head to the base, because corn topples for two very different reasons. Shallow roots in loose soil simply lose their grip in heavy wind, while small entry holes ringed with sawdust-like frass mean a corn borer has tunneled the stalk from the inside out. Stand the plants back up and hill soil around the base, then shred and till in those old stalks at season's end to wipe out the borers that overwinter in there.
Fix:
- Gently stand plants back up and hill soil around the base after storms
- Destroy crop residue after harvest to remove overwintering borers
Orange rust patches and long tan streaks crossing the foliage
Orange spots that smudge off on your fingers are common rust, and long cigar-shaped gray-tan streaks usually flag northern corn leaf blight when warm, humid weather rolls in. Good news late in the season: neither does real harm, so you can let them ride. Pull the worst lower leaves to tidy things up, and load up on resistant hybrids next year to stay a jump ahead.
Fix:
- Remove heavily infected lower leaves
- Severe cases on young plants may warrant a labeled fungicide; late-season infection rarely needs treatment
Toxicity
Great news right off the bat: sweet corn is safe. No part of the plant is poisonous to people, pets, or livestock, which is exactly why it lands on dinner plates and in animal feed alike. The one thing to watch is the bare cob, since a dog can swallow one and choke 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 at all. A cat that chews a leaf or a stray kernel runs into no danger from the plant itself.
Dogs None
The plant won't poison a dog, but the cob brings a hazard of its own kind. A swallowed cob or chunk can jam in the gut and block it, so stash whole cobs well out of reach.
Horses Safe
Grain corn shows up in feed all the time, and the plant carries nothing that would trouble a horse.
Rabbits Safe
Let a rabbit nibble away, though it thrives most on leafy greens with just a little corn here and there.
Livestock Safe
Corn has powered cattle, sheep, and goats for generations and packs no toxin for any of them.
Birds Safe
Hens and wild birds dive into the kernels happily, and nothing in the plant will harm them.
People Safe
Sweet corn is a summer kitchen star, 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. Here are a few well worth knowing by name.
Silver Queen
A classic standard white prized for flavor that delivers in roughly 88 to 92 days.
Bodacious
A sugary-enhanced yellow packed with tender, sweet kernels ready around 75 days.
Ambrosia
A sugary-enhanced bicolor of yellow and white kernels, also about 75 days, and a runaway home-garden favorite.
How Sweet It Is
A supersweet white that holds its sugar longest after picking, as long as it gets warm soil and stays clear of 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 grows 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 makes growing a breeze, since you sow it straight where it will grow and skip transplanting, which it never enjoys anyway. Drop the seeds 1 to 1.5 inches deep and 8 to 12 inches apart in a block of three or four rows so the wind can pollinate them, and they shoot up in about 4 to 10 days once the soil warms. Keep the ears rolling by sowing a fresh patch every 2 to 3 weeks, and park any supersweet variety well away from other types, since cross-pollination turns the kernels starchy.
Myths
Ripping out the shoots crowding the stalk base makes the plant produce more ears.
Those base shoots, the tillers or suckers, do zero harm when you let them stand. Yanking them off gains you nothing and the open wounds can stress the plant or hand disease a way in, so leave the tillers alone.
Plant one long row and it fills perfectly well if the plants seem healthy.
Corn pollinates on the wind, and every silk needs its grain of pollen to set a kernel. One row catches far too little and the ears come in gappy, so plant in blocks of at least three or four short rows and watch them fill.