Vegetable · Poaceae
Sweet Corn
Zea mays
Grow it in a block, not a row, feed it well, and sweet corn swells full, milky kernels under brown silk 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 that rises on a single ribbed stalk and unfurls long, strap-shaped leaves that arch outward as it climbs toward its summer ears. 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. Sun, warmth, and rich ground let even a few square feet throw up stalks heavy with grain.
Corn carries its flowers in two places, and that split shapes how it sets seed. Feathery tassels branch from the very top and shed dry pollen, which drifts onto the fine silks trailing from the young ears below, and each silk runs down to a single kernel waiting to swell. A lone row or a single plant catches too little drifting pollen, so a block of several short rows lets the wind dust every silk and fill each ear from butt to tip.
Corn is a hungry plant beneath its lean green look. It pulls steadily at water and at nitrogen, and it sulks in cold soil or close quarters. Matched timing and feeding push the stalk up fast and pack the cob, but stinted, the ear comes off the husk gappy and half-filled, its kernels scattered and shrunken instead of glossy and tight.
Care
The short version: corn wants full sun, rich soil, and plenty of water, set in a block rather than a single row so the wind can dust the silks with pollen. It is a heavy nitrogen feeder, so feed it well, and hold the soil moist once the silks trail from the ears.
Light
Corn drinks in full sun, the more the better, with no shade falling across it. Its tall stalk and broad arching leaves already cast a shade of their own, so the open, sunniest ground suits it best.
Water
Hold the soil evenly moist, near an inch of water a week. The plant thirsts most from tasseling and silking through ear fill, the stretch when a dry spell leaves the cob with poorly filled ears, its sockets empty and its kernels flat.
Soil
Sink the roots into fertile, well drained loam worked full of organic matter. A pH of 6.0 to 6.8 suits it best, and the rich, dark ground feeds the heavy appetite the stalk carries.
Temperature
Corn ranges across a wide band, from about 50°F to 95°F (10°C to 35°C), but it needs warm soil to crack the kernel and a long warm stretch to ripen the ear. In cold ground the seed rots before the green spear can show.
Humidity
Plain outdoor air is humidity enough, so there is no figure to chase. What carries the day is the wind, lifting dry pollen off the tassels and sifting it down onto the silks to fill out the ears.
Feeding
Corn is a heavy nitrogen feeder, its tall green growth always asking for more. A balanced fertilizer works in at planting, then a nitrogen side-dressing once the stalk stands about a foot tall and again as the tassels open.
Pruning
There is nothing to prune off the plant. The slim tillers sprouting at the foot of the stalk stay put, since cutting them raises no yield and can lower it, and only the swollen smut galls or clearly diseased stalks call for the knife.
Size & spacing
The ribbed stalks rise 5 to 8 feet (150 to 250 cm) tall on a narrow base, so the plants stand 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 so the tassels can dust every silk.
When to plant
Corn lives on warmth and blackens at the touch of frost, so the kernel waits in the packet until the cold is gone. Once the soil has warmed to at least 60°F (16°C), the seed goes straight into the ground to swell and split. A fresh patch every couple of weeks keeps new silk-topped ears forming 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 of corn's troubles surface on the ears and the tall stalks, and a good share trace back to how the plant was set out rather than to any pest. Read the early marks on husk, blade, and stem, and you can still save the crop, or at least the ears already swelling on the plant. Match what you see below, then act while it counts.
Gnawed, ragged kernels and a caterpillar at the ear tip
The plump caterpillar burrowed among the kernels at the crown of the ear is the corn earworm, which slid down the silk channel to feed where the cob is softest. Its chewing and dark frass stay packed into the top few inches, so the tip lifts away and leaves clean, milky kernels below. A few drops of mineral oil beaded onto the silks a few days after they appear, or a film of Bt brushed over fresh silk, blocks the next ones at the door.
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 pocked with empty gaps and shrunken kernels
An ear pocked with empty sockets and flat, shrunken kernels is the face of poor pollination, the mark of silks that drew no pollen because a single row left the wind too little to scatter. A dry stretch during silking shrivels still more. Set the plants in a block of three or four short rows, hold the soil moist once the tassels lift, and dust the silks by hand with a shake of the tassels to plump out a thin patch.
Fix:
- Water deeply during silking and ear fill
- Hand-pollinate small plantings by shaking tassels over fresh silks
Bulging silver-gray galls splitting into powdery black spores
The bulging gray-white lumps swelling on ears, tassels, and stalks are common smut, a fungus that creeps in through wounds and runs through hot, dry weather and a heavy load of nitrogen. Each gall starts firm and silvery, taut as a balloon, then darkens, softens, and splits to spill a powdery black cloud of spores. Slice them off and seal them in the trash while they are still firm and whole, and keep them clear of the compost.
Fix:
- Remove and destroy galls before they rupture; do not compost them
Stalks keeling over or snapping along the stem in wind
When the tall green stalks lean or snap, the base of each one tells the story, because corn goes down for two separate reasons. Shallow roots gripping loose soil tear free in a storm, while a ring of sawdust-like frass around a small bored hole marks where a corn borer has hollowed the stalk from the inside. Ease the leaning plants upright and mound soil over the roots, then shred and turn in the spent stalks at season's end to clear out the borers tucked away to overwinter.
Fix:
- Gently stand plants back up and hill soil around the base after storms
- Destroy crop residue after harvest to remove overwintering borers
Rust-orange pustules and long tan streaks banding the leaves
Raised orange pustules that powder a fingertip rust-colored are common rust, while long, gray-tan lesions tapered like cigars across the blade signal northern corn leaf blight in warm, humid weather. By late season neither mark cuts into the harvest, and the spotted leaves can simply hang on. Strip the most freckled lower blades, and reach for resistant hybrids next year to keep the foliage cleaner.
Fix:
- Remove heavily infected lower leaves
- Severe cases on young plants may warrant a labeled fungicide; late-season infection rarely needs treatment
Toxicity
The reassuring word first: sweet corn is safe. No part of the plant, from strappy leaf to milky kernel, is poisonous to people, pets, or livestock, which is why it fills both dinner plates and feed buckets. The one thing to watch is the bare, stripped cob, woody enough that a dog can swallow it 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 runs through leaf, stalk, or kernel. A cat that gnaws a strappy green blade or a dropped kernel meets no danger from the plant itself.
Dogs None
Nothing in the plant poisons a dog, but the woody, stripped cob is a hazard of its own. A swallowed cob or a snapped-off chunk can wedge in the gut and block it, so keep the bare cobs well out of reach.
Horses Safe
Grain corn fills many a feed bucket, and the plant carries no toxin to trouble a horse.
Rabbits Safe
A rabbit can crop the leaves safely, though it fares best on leafy greens with only a little corn now and then.
Livestock Safe
Corn has filled the troughs of cattle, sheep, and goats for generations and holds no toxin for any of them.
Birds Safe
Hens and wild birds peck the golden kernels eagerly, and nothing in the plant can harm them.
People Safe
Sweet corn is a kitchen staple, the milky kernels 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 the sugar in its kernel a little differently after picking. A few are worth knowing by name.
Silver Queen
A classic standard white whose pale, milky kernels are grown for flavor, ripening in roughly 88 to 92 days.
Bodacious
A sugary-enhanced yellow set with tender, sweet kernels that come ready around 75 days.
Ambrosia
A sugary-enhanced bicolor whose cobs mix yellow and white kernels, also about 75 days, and a favorite in home gardens.
How Sweet It Is
A supersweet white that keeps its sugar longest in the picked kernel, asking for warm soil and 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 comes up one way, from the hard kernel sown right where it will stand, since its roots resent being 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 rises straight from the hard, dimpled kernel pressed into the bed where it will stand, since its roots resent being lifted and moved. 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 sift pollen across them, and the first pale green spears split the soil in about 4 to 10 days once it is warm. A fresh patch every 2 to 3 weeks keeps new ears swelling, and a supersweet variety wants distance from other types, since cross-pollination leaves its kernels starchy.
Myths
Pinching out the shoots clustered around the stalk base grows more corn.
The slim shoots branching from the foot of the stalk, the tillers or suckers, do no harm left where they are. Tearing them off raises no yield, and the torn green wounds can stress the plant or open a path for disease, so leave the tillers alone.
A lone long row fills its ears completely if the plants look vigorous.
Corn rides the wind to pollinate, the dry pollen sifting from the tassels onto the threadlike silks, and each silk needs one grain to swell a kernel. A single row catches too little and the cob comes in pitted and gappy, so plant in blocks of at least three or four short rows.