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Planting, Growing, and Harvesting Sweet Corn
Planting
The most common reasons for slow growth include poor light levels, not enough moisture, or a lack of nutrients. Plant in full sun (at least 6 to 8 hours of direct sunlight). Soil needs to be consistently moist (though well-draining),as corn tends to suck up a lot of water. Corn is a hungry plant, so it’s important to enrich beds with lots of organic matter, such as garden compost (ideally in the fall).
When to Plant Corn
- Most gardeners sow corn directly in the garden soil (versus indoors) so that their sensitive roots aren’t disturbed when transplanting.
- Corn is very sensitive to frost; do not plant soil temperature is at least 60°F (16°C), or 65°F (18°C) for super-sweet varieties. Usually, this is 2 or 3 weeks after the last frost in spring. See our Planting Calendar for corn based on average frost dates.
- If you live in an area with a shorter growing season, choose an early variety that will mature well before the first fall frost. The ground can be warmed by a black plastic cover; sow seeds through holes in the plastic.
- A couple of weeks after planting your first round of corn, plant another round in order to extend the harvest.
How to Plant Corn
- To speed germination, moisten seeds, wrap them in moist paper towels, and store them in a plastic bag for 24 hours.
- Because corn is wind-pollinated, it’s essential to plant in a block, rather than a single row. For decent pollination, we recommend a modest block of, say, 10 to 50 plants. This maximizes the chances of the pollen released from the male tassels at the top of the plants drifting down into contact with the female silks lower down. Incomplete or inconsistent kernel development, with the cobs only partly or sporadically filled, is down to poor pollination. The silks protruding from the end of each cob are responsible for carrying the pollen down to the kernels. One strand connects to one kernel, so for complete fill, every strand of the silk must be pollinated.
- Sow seeds about 1½ to 2 inches deep and 12 inches apart in rows 2½ to 3 feet apart. Don’t plant too close together or you run the risk of disappointingly small cobs.
- You may choose to fertilize at planting time with a general purpose (10-10-10 fertilizer); corn is meant to grow rapidly.
- Water well at planting time.
Sowing Corn Indoors
If you’re going to start seeds early, sow the seeds in pots under the protection of a greenhouse, hoop house, or cold frame. This means you can begin sowing three to four weeks before your last frost date, giving you a head start on corn sown outdoors—a huge advantage for areas with shorter growing seasons.
Sow eight to ten seeds half an inch deep into four-inch-wide pots, or sow two seeds per module in a plug tray and remove the weakest of the two seedlings when they emerge. Keep the potting soil moist as they grow on.
Harden off the plants as your recommended planting time approaches by placing them outside for increasingly longer spells over the course of about a week. Plants should be at least six inches tall by the time they’re transplanted outdoors.
Check out this video for great tips on growing juicy corn:
Types
Types of Sweet Corn
There are four main types of hybrid sweet corn: sugary (su), sugar-enhanced (se), shrunken (sh, sh2), and synergistic (sy). Each one contains a different level of sucrose, changing the flavor and texture of the corn.The type of corn will be listed right on the seed packet.
It’s important to be aware of which type of corn you’re growing—not only because of the sugar content, but also due to how easily the types can cross-pollinate. If the wrong combination of types cross-pollinates, the ears that are produced may be of subpar quality.
- Sugary (su) sweet corn is the classic sweet corn. Sugary varieties grow vigorously and are stress resistant. The kernels aren’t too sweet and are said to have a “traditional” taste. However, the sugars in sugary sweet corn quickly turn to starch after the ears are picked, so they need to be eaten right after picking. Do not plant near shrunken or synergistic types.
- Sugar-enhanced (se) sweet corn is slightly sweeter than sugary varieties. They keep their sweetness for a longer period of time after harvest (a few days) than sugary varieties. They grow well with few issues. Do not plant near shrunken types.
- Shrunken (sh, sh2) sweet corn—also called “supersweet”—are the sweetest varieties, containing two to three times more sugar than sugary varieties. The sugar in their kernels lasts even longer after harvest (up to a week) than the other types, but kernels tend to be more crunchy and not taste as “corny.” Shrunken types are also more finicky overall. Do not plant them near any other types; hybrid kernels turn out starchy and tough.
- Synergistic (sy) sweet corn combines sugar-enhanced with one of the other two types to create varieties that have the best of both worlds. Synergistic types tend to have very sweet, tender kernels with a good taste and some synergistic varieties can keep up to a week after harvest. Do not plant near sugary or shrunken types.
Recommended varieties include:
- ‘AԳ’: sugar-enhanced variety, good taste. White kernels.
- ҵdz’: midseason, normal-sugar variety. Yellow kernels.
- ‘Luther Hill’: dwarf, normal-sugar variety. Produces 4- to 6-inch ears on 4- to 5-foot stalks. White kernels. Grow at least nine dwarf plants in a block of three or four rows.
- ‘Silver Queen’: normal-sugar variety. Resistant to some bacterial diseases. White kernels.
- ‘Sweet Sunshine’: supersweet variety. Disease resistant and high yield. Yellow kernels.
Corn can be a feast for the eyes, too! Look for these ornamental varieties:
- ‘Glass Gem’: Sporting multi-colored, semi-transparent kernels, this is a favorite for kids.
- ‘Painted Mountain’: Looking for the classic “maize” colors? This variety has a great diversity of natural tones.
Harvesting
- The warmer the air, the more quickly corn matures. It is usually ripe about 15 to 23 days after silking and sooner if temperatures are exceptionally high.
- When two ears grow on a stalk, the upper ear matures 1 to 2 days before the lower one.
- At harvest, ears should be rounded or blunt, not pointed, with tassels turning brown and kernels full and milky.
- To test, pull down some husk and pierce a kernel with a fingernail. If it’s white, or milky, it’s ready. The milk stage is brief; in hot weather (over 85°F/29°C), sweet corn is at peak for only 1 to 2 days, so check it frequently. Corn harvested a few days after milk stage will not be as sweet.
- Pull ears downward and twist to remove from stalk.
- Sweet corn varieties (except for supersweet varieties) lose their sweetness soon after harvest. Immediately after picking, prepare the ears for eating or preservation.
- Prepare for eating or preserving immediately after picking. Enjoy your harvested corncobs as soon as you can. The quicker they’re cooked, the sweeter they will be!
- If immature corn suffers a late-season frost, the plants and cobs can be damaged and result in the death of the plant or poor-tasting corn.
How to Store Corn
- Sweet corn freezes well, especially if removed from ears before freezing. Learn how to properly freeze corn.
- Corn can also be harvested for other purposes!
Cooking Notes
- If too much hot pepper or spice has been added to a soup or stew, adding a can of sweet corn can help.
- Popcorn is also a favorite snack if you have leftover kernels. Learn how to make homemade popcorn here.
Catherine Boeckmann
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Most of the sweencorn plants have some cobs coming, but some which we have grown in a very large container have no cobs at all. These are very strong plants and have lush green leaves but no cobs, Could you please tell me what I have done wrong.
Thanks.
Alyson.
Good day! I had a wonderful harvest of corn this year and have run into the end of my growing cycle and have harvested all of my corn as it started to get the starch flavor. Is it possible to plant again at this time of year (August 14th) and get a second yield? I am a newbie gardener and apologize if this question is non-sensible but everything i have looked at only really states when to plant your one crop for the summer. Just wondering if i could get lucky with a late fall crop or if it is a waste of time and i should plant something else. I have optimum soil / light etc and had the stalks above my shoulder by July 4th this year. "Knee high by 4th of July" didn't apply to my crop at all. Am i crazy? I'm in New Hampshire. Would appreciate any and all feedback. Thanks!
Hi Nick,
Glad to hear about your successful corn crop! August is a bit too late to be planting a second crop in NH since the first expected frost is around Sept. 20. It would be better to plant some frost-hardy cole crops or lettuce in their place.
We planted a few rows of corn in the garden, and somehow the stalks got bent over (we suspect it was the sparrows who were jumping up and down on them.) Now instead of standing straight up with the tassels at the top, some are bent, above where the ear is growing. Our question is, will this affect the growth of the ears? We tried propping them up but it doesn't really work. Thanks so much.
Hi Karen,
Bent stalks and tassels can also be signs of corn borer damage. If you already have ears growing your corn may be doing OK with no need to straighten the stalks.
I planted corn in containers It tasseled out and not one ear of corn on about 30 stalks. Why?
We are located in southeast Tennessee and for the first time planted some sugar baby corn. We have just eight stalks and they were doing great, a couple of ears on each, verying in size. Each ear had beards of silk and looked great. We left town for week and there were heavy rains most every day, when we returned all the silk is brown, even on the very smallest, one just barely a few inches long with a few silk strands. We didn't realize the need to count days to harvest but it has been around sixty days. I picked a few of the larger ears and had no bugs and kernels plump and popped with finger nail test, all seams to be good except for the question of the remaining ears. Will the ears continue to grow to maturity even though the silk is brown? Was this caused by all the rain?
Thanks
When the silk turns brown the kernals are getting close to being ripe. The small cobs are probably not going to grow much bigger. You need to check the kernels for ripness before you harvest the last of your corn. The rain did not turn the silk brown.
Thank You, Staff, for you response!
My friend came back today and looked at our garden. She saw the tassels on top of our corn stalks and said we were suppose to cut them off when they first come out to help the corn. Is this true?
