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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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Which is the best variety of corn for eating to grow in zone 5a?
Hi,
we have grown tall, healthy looking corn all with cobs on them. The silks have turned brown but upon opening them they have very few yellow kernels. The rest are unripened, white and flat. Do we just need to be more patient or do we need to help them pollinate? If so, how do we do this?! Thank you
It is due to lack of pollination - probably too windy when pollination occurred. After the tassels have opened up run your hand up the tassel collecting the pollen and then rub on the silks of the cob. Do this when there is little wind in the morning. The pollen is microscopic. Try and plant in a spot that is protected from the wind a bit if you can.
Brown silks are one sign that corn is maturing; also check the kernels themselves. If you puncture one with your fingernail, it should exude a milky liquid. If it is clear, it is not ready yet. However, there are also several diseases, pests, and cultural/environmental problems that can cause the same effect. Drought stress, for example, can interfere with pollination, and so can the feeding habits of certain insects. For in-depth information about corn ear problems—you might visit this page from the Ohio State University:
http://u.osu.edu/mastercorn/
I have read on the old farmer's almanac that I should plant corn seeds 1" deep and 4 to 6" apart.
In the care section it states when your plants are 3 to " tall, thin them so they are 8 to 12" apart.
Does this mean I have to up root every other plant to be able to obtain the minimum 8 inches, or what exactly does this mean?
Thank You,
JV.
When the seedlings get to be 3 to 4 inches tall, remove seedlings (choose the weakest to remove, if you have the option) so that the spacing is now between 8 and 12 inches apart, giving the remaining plants enough room to mature healthily. If you have a vigorous variety, the larger spacing (12 inches) might be better. So, if you’ve planted at 4-inch spacing, remove every other to obtain 8-inch spacing; as a diagram, with uppercase “X” being the plants you want to keep and lowercase “x” for those you remove: X x X x X x X. Or, if you’ve planted at 4-inch spacing, you can also choose a larger spacing, such as 12 inches; in this case, you’d remove the 2nd and 3rd plant out of every 4: X x x X x x X x x X
Because some seeds may not germinate, some seedlings may be weak, some may be eaten by pests, etc., planting more corn initially, at a closer spacing (4 to 6 inches), gives you a better chance of getting the most corn for your space after thinning (8 to 12 inches).
We planted bi-color sweet corn, for the first time. It has been delicious and of good size, but 2 of the ears, were a little flexible. Why is that? Thank you.
Some varieties of corn naturally have a more flexible cob, but pests, diseases, environmental conditions, or nutrient deficiencies can sometimes make the cob softer than normal.
This is my first real garden and growing Veggies. 1) zucchini 2) corn 3)peas 4)cucumbers 5)Blue lake green Beans 6 Tomatoes ( Roma ).. So please tell me about the corn beetle ?
Do you mean the corn flea beetle? These pests attack corn seedlings in May and June. They can transmit bacterial wilt. Damage is usually minimal, but they cause many tiny holes in leaves, and tiny bleached lines or circles. Adults are tiny and black, and hop about. For more information about flea beetles, see: http://www.almanac.com/pest/flea-beetles
Japanese beetles, on the other hand, are much larger, metallic blue-green beetles that emerge around June and July; they can skeletonize leaves of many plants, leaving almost nothing except the leaf veins; on corn, they may nibble on corn silk and tassels. For more information about these pests, see: http://www.almanac.com/pest/japanese-beetles
