Fresh sweet corn eaten within an hour of picking tastes nothing like store-bought. Corn is a warm-season grass that needs full sun, warm soil, plenty of nitrogen and water, and, most important, enough plants grouped together to pollinate one another. This page covers when to sow, how to lay out a planting so ears fill out, how to care for it and how to tell when it is ready.
Sweet corn at a glance
| Type | Vegetable |
|---|---|
| Season | Warm-season |
| Sun | Full sun |
| Plant spacing | 12 in |
| Row spacing | 30 in |
| Per square foot | 1 |
| Seed depth | 1.5 in |
| Days to maturity | 70–100 from seed |
| How to start | Direct sow 1–2 weeks after last frost |
| Water | 1.5 in per week |
These are the same numbers our plant spacing, square foot and harvest date calculators use. See every crop in the plant database.
When to plant sweet corn
Sow corn directly outdoors 1 to 2 weeks after your last spring frost, once the soil has reached at least 60°F. Supersweet varieties need warmer soil, about 65°F, or the seed rots. For a longer harvest, sow a new block every 2 weeks until about 3 months before your first fall frost, or plant early, mid and late varieties on the same day.
Check your frost dates with the frost dates by ZIP code tool. The succession planting planner lays out the sowing dates.
How to plant sweet corn
- Plant in blocks, not one long row. Corn is pollinated by wind: pollen falls from the tassels onto the silks. A block of at least 4 short rows side by side gives much better pollination and fuller ears than one long row.
- Sow 1 to 1 1/2 inches deep. Use the spacing in the table above. The plant spacing calculator sets out a block for your bed.
- Keep types apart. Supersweet corn crossed with regular or sugary-enhanced types turns starchy. Separate them by about 250 feet, or sow them at least 2 weeks apart so they tassel at different times.
- Feed the soil. Corn is a heavy nitrogen feeder; work in compost before sowing.
Caring for sweet corn
Corn needs about 1 to 1 1/2 inches of water a week, and the most important time is from tasseling until the ears fill. Dry soil at that stage gives poorly filled ears. Water deeply at the base, and mulch to hold moisture. The garden watering calculator turns this into gallons for your block.
Side-dress with a nitrogen fertilizer or compost when plants are knee high and again when tassels appear. Weed carefully while plants are small, because corn has shallow roots. Do not remove the side shoots (suckers) at the base; they do no harm.
Companion plants
| Grow nearby | Pole beans, squash, pumpkins, cucumbers, melons |
|---|---|
| Keep apart | Tomatoes (corn earworm also feeds on tomatoes); low crops on corn's north side, which it shades |
Corn, beans and squash are the traditional Three Sisters: beans climb the stalks and add nitrogen, and squash leaves shade the soil. Cucumbers and melons enjoy the light shade beside the block. Check other pairings with the companion plant finder.
Common problems
| Problem | What you see | What to do |
|---|---|---|
| Poorly filled ears | Ears with missing or scattered kernels | Poor pollination. Plant in blocks of 4 or more rows and keep the soil moist while tassels and silks form. |
| Corn earworm | Caterpillars and droppings at the tip of the ear | Put a few drops of mineral oil on the silks 5 to 6 days after they appear. Cut off damaged tips; the rest of the ear is fine. See the pest identifier. |
| Raccoons and birds | Stalks pulled down and ears eaten, often the night before you planned to pick | Fence the block, or cover each ear with a paper bag after pollination. |
| Corn smut | Large gray swellings on ears, tassels or stalks | Remove swellings before they burst and release spores. Rotate corn to a new spot. |
| Seed rots, poor stand | Few seedlings come up | Soil was too cold. Wait for 60°F soil, or 65°F for supersweet types. |
Not sure what you are looking at? The plant problem identifier ranks likely causes from the symptoms you see.
When and how to harvest
Sweet corn is usually ready about 18 to 24 days after the silks first appear. Look for silks that have turned brown and dry, ears that feel full and rounded at the tip, and a tight green husk. Peel back a little of the husk and press a kernel with your thumbnail: milky juice means it is ready, clear juice means wait a few days, and paste means it is past its best.
Twist the ear down and pull it off the stalk. Eat or chill it as quickly as possible, because the sugar in standard varieties starts turning to starch within hours of picking. Use the harvest date calculator to estimate your harvest.
Plan your sweet corn
- Plant spacing calculator: how many plants fit your bed
- Planting calendar: sowing and transplant dates for your frost dates
- Frost dates by ZIP code: your last spring and first fall frost
- Harvest date calculator: when your crop will be ready
Frequently asked questions
How far apart should I plant sweet corn?
Space sweet corn 12 inches apart in rows 30 inches apart. In a square foot garden, plant 1 per square foot.
How deep do I plant corn seeds?
Sow seeds 1.5 inches deep.
How long does sweet corn take to grow?
Most varieties are ready 70–100 days from seed. Check the seed packet, because early and late varieties differ.
How much water does sweet corn need?
About 1.5 inches of water a week, from rain and watering combined. Water is most critical from tasseling until the ears fill out.
Why should corn be planted in blocks?
Corn is pollinated by wind. A block of at least 4 short rows lets pollen fall from the tassels onto the silks of nearby plants, so ears fill out fully.
How do I know when sweet corn is ready to pick?
About 3 weeks after silking, when the silks are brown and dry and a punctured kernel gives milky juice.