Vegetable · Poaceae
Sweet Corn
Zea mays
Set it in a block, not a row, feed it generously, and sweet corn will reward you with full, 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 you grow for the sugary ears it offers in high summer, and it is far more forgiving than its size might suggest. It traces back to the Americas, where people bred it from wild grasses thousands of years ago, and today it settles happily as a warm season annual in gardens almost everywhere. Give it sun, warmth, and rich ground, and even a few square feet can hand you a true summer crop.
The one thing corn asks that most vegetables skip is a little company, and once you know this you are most of the way there. It pollinates on the wind, with pollen drifting down from the tassels onto the silks below, so a lone row or a single plant sets poorly through no fault of yours. Plant it in a block of several short rows and the wind quietly does the work, filling every ear from butt to tip.
Corn does have a healthy appetite, but that is easy to meet once you expect it. It wants steady water and a generous hand with nitrogen, and it grows impatient with cold soil and crowding. Get the timing and the feeding right, and it rewards you by growing fast; let those slip and the ears come in gappy and half-filled, which is a hint, not a verdict, and an easy thing to put right next time.
Care
The short version: give it 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 the soil moist once the silks appear.
Light
Corn loves full sun and the more it gets the happier it is, with no shade to speak of. Being tall and quick to grow, it casts enough shade on itself already, so hand it the open, sunniest spot you have and it will thank you.
Water
Keep the soil evenly moist, aiming for about an inch of water a week, and you can relax between drinks. Moisture counts most from tasseling and silking through ear fill, since a dry spell at that stage is what leaves you with poorly filled ears.
Soil
Plant it in fertile, well drained loam with plenty of organic matter worked in, and your corn will hardly want for more. A pH of 6.0 to 6.8 suits it best, and that rich ground is just what feeds the hearty appetite corn brings.
Temperature
Corn is content across a wide band, from about 50°F to 95°F (10°C to 35°C), though it needs warm soil to get going and a long warm stretch to ripen. Sow into cold ground and the seed simply rots before it can sprout, so a little patience pays off.
Humidity
Ordinary outdoor humidity is all corn asks for, so there is no number to fuss over here. What truly matters is the wind, which carries pollen from tassel to silk and fills out those ears for you.
Feeding
Corn is a heavy nitrogen feeder, so feed it generously and it will reward you. 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
Happily, there is nothing to prune. Leave the tillers that sprout at the base of the stalks just as they are, since taking them off does not raise yield and can lower it. The only things to cut out are smut galls or stalks that are clearly diseased.
Size & spacing
Stalks stand 5 to 8 feet (150 to 250 cm) tall yet take up little width, so you can set the plants close, about 8 to 12 inches (20 to 30 cm) apart. Gather them into a block of several short rows rather than one long line, and the wind will reach every silk.
When to plant
Corn lives by warmth and simply cannot weather frost, so timing is the one thing worth getting right. Wait until the cold has passed and the soil has warmed to at least 60°F (16°C), then sow the seed straight into the ground with confidence. Pop in a fresh patch every couple of weeks and you will 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 turns up on the ears or the stalks, and a good deal of it comes down to how the plant was set out rather than to any pest, which is good news because that part is in your hands. Spot the early signs and you can often save the crop, or at least the cobs already on the plant. Match what you see below, then act while it still does some good.
A caterpillar and some chewed kernels up in the ear tip
Finding a caterpillar and nibbled kernels up top is almost always the corn earworm, which slides down the silk channel and settles in to feed at the very tip. Take heart, because the harm rarely reaches past those first few inches, so you can simply trim the tip away and enjoy the rest of the cob. To spare the next ears, dab a few drops of mineral oil on the silks a few days after they show, or give them a light 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
Ears coming in patchy, with empty spots and shriveled kernels
Gaps and shriveled spots come down to poor pollination, and the usual cause is a single row that the wind cannot carry pollen across to every silk. A dry spell during silking only adds to it. Don't worry, the fix is gentle: next season set the plants in a block of three or four short rows, keep the soil moist once the tassels appear, and you can even shake the tassels over the silks by hand to fill in a thin patch.
Fix:
- Water deeply during silking and ear fill
- Hand-pollinate small plantings by shaking tassels over fresh silks
Puffy gray galls that split open into black dust
Those puffy growths are common smut, a fungus that finds its way in through small wounds and spreads in hot, dry weather, especially when nitrogen has been laid on heavy. They begin firm and silvery, then darken and split open to scatter powdery black spores. It looks dramatic, but you have time: cut the galls out and bag them before they burst, and please keep them out of the compost.
Fix:
- Remove and destroy galls before they rupture; do not compost them
Stalks leaning over or breaking in a gust
Before you blame the storm, take a calm look at the base, because corn falls for two different reasons. Shallow roots in loose soil simply give way in heavy wind, while small entry holes ringed with sawdust-like frass tell you a corn borer has been tunneling the stalk from the inside. Gently stand the plants back up and mound soil around the base, and at season's end shred and till in the old stalks so the borers that overwinter there don't get a head start.
Fix:
- Gently stand plants back up and hill soil around the base after storms
- Destroy crop residue after harvest to remove overwintering borers
Orange rusty flecks or long tan blotches across the leaves
Powdery orange spots that smudge off on your fingers are common rust, while long cigar-shaped gray-tan streaks usually mean northern corn leaf blight during warm, humid stretches. The reassuring part is that late in the season neither one does much real harm, so you can often just leave them be. If you like, pull off the worst of the lower leaves, and pick resistant hybrids next year to stay a step ahead.
Fix:
- Remove heavily infected lower leaves
- Severe cases on young plants may warrant a labeled fungicide; late-season infection rarely needs treatment
Toxicity
Here is the reassuring part: 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 worth a small caution 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
Rest easy, there is no poison in this plant. Should a cat chew a leaf or a dropped kernel, the plant itself can do it no harm.
Dogs None
A dog won't be poisoned by the plant, yet the cob is a real hazard of a different sort. A swallowed cob or a chunk of one can lodge in the gut and block it, so it helps to keep whole cobs well out of paw's reach.
Horses Safe
Grain corn is a familiar feed, and the plant carries nothing that would trouble a horse.
Rabbits Safe
It is fine for a rabbit to nibble, though they do best on leafy greens with only a little corn here and there.
Livestock Safe
Corn has nourished cattle, sheep, and goats for generations and holds no toxin for any of them.
Birds Safe
Hens and wild birds tuck into the kernels with pleasure, and nothing in the plant will harm them.
People Safe
Sweet corn is a kitchen favorite, eaten fresh from the cob or cooked, with no part of it that you need to avoid.
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 once it is picked. Here are a few that are well worth knowing by name.
Silver Queen
A much-loved standard white that gardeners grow for sheer flavor, ready in roughly 88 to 92 days.
Bodacious
A sugary-enhanced yellow with tender, sweet kernels that you can pick around 75 days.
Ambrosia
A sugary-enhanced bicolor of yellow and white kernels, also ready in about 75 days, and a real home-garden favorite.
How Sweet It Is
A supersweet white that keeps its sugar longest after picking, asking only for warm soil and a little distance 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 simple way, from seed sown right where it will stand, since it would rather not have 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
Take comfort that corn is one of the simplest crops to start, since you sow it straight where it will grow and skip the fuss of transplanting it dislikes. Tuck 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 push up in about 4 to 10 days once the soil is warm. Sow a fresh little patch every 2 to 3 weeks to keep ears coming, and just remember to keep any supersweet variety well away from other types, since cross-pollination turns the kernels starchy.
Myths
Stripping the little shoots from the stalk's base will get you a bigger harvest.
Those little base shoots, the tillers or suckers, do no harm at all if you simply let them be. Pulling them off gains you nothing in yield, and the open wounds can stress the plant or invite disease, so leave the tillers alone.
One long single row will fill out just fine, provided the plants look strong.
Corn leans on the wind for pollination, and each silk needs its own grain of pollen to make a kernel. A lone row catches too little, which leaves you with gappy ears, so plant in blocks of at least three or four short rows and let the wind do the rest.