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How to Grow: Sweet Corn
Learn how to plant and grow sweet corn.
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There’s is nothing more all-American than sweet corn (Zea mays). I remember working on an organic farm when I was younger an discovering just how sweet, sweet corn is. I would be harvesting ears for market and whenever I got hungry I would just peel (shuck) and eat the corn raw right in the field. The flavor was sweeter than any cooked corn I ever ate.
Most gardeners think they need a large field to grow corn. Actually the key with growing sweet corn is to plant in small blocks or multiple short rows, to maximize pollination. Also, grow different varieties. Early, mid, and late-season varieties extend the time you’ll have sweet corn to eat. Traditional varieties lose their sweetness quickly after harvest. However, newer sugar-enhanced and supersweet varieties stay sweet longer not requiring you to sprint from field to kitchen to cook it as fast as possible. However, they require warmer soils and are a little more demanding to grow.
While most gardeners think of eating sweet corn steamed, corn is also good roasted. I like to shred the kernels and freeze them for use in winter in soups, breads, and salads.
When to Plant
Sweet corn is a warm season crop so don’t hurry to plant it in spring. Direct sow seeds into the garden 2 weeks after the last frost date in your area. That would be May or early June. The soil needs to be at least 60F for germination, but the warmer the better.
Where to Plant
Sweet corn grows best in full sun on fertile, well-drained soil. Since corn grows so tall (up to 7 feet), plant it on the north side of your garden where it won’t shade other vegetables.
How to Plant
Sweet corn is actually in the grass family. Like a lawn it needs a rich soil high in nitrogen to grow its best. Amend the soil before planting with a thick layer of compost. Ideally plant it in a location that had a legume, such as peas or beans, growing last season. Legumes add nitrogen to the soil and corn is the prefect vegetable to take advantage of it the next year. Sow seeds 8- to 12-inches apart spaced 2- to 3-feet apart. To insure germination, soak seeds overnight in warm water to pre-sprout them.
While the Northeast tribes of Native Americans perfected growing corn in hills, in the modern home garden growing in blocks is best. A block is at least 4, 10 foot long rows. Make the walkway between blocks 3- to 4-feet wide so they’re easier to navigate. A block helps prevent the corn from blowing over during a thunderstorm and also makes for better pollination. The tassels (tops) need to drop pollen on the silks (hairs) of ears in order for complete pollination to occur. Every kernel in an ear of corn needs a pollen grain in order to form. If you even saw an ear that had some “teeth” missing, that’s improper pollination. Plant blocks of all one variety so they don’t cross pollinate with each other. If you’re seeing yellow kernels in your white sweet corn, that’s cross pollination. This is particularly important for the supersweet varieties. If they cross pollinate with traditional varieties, you’ll lose some of the added sweetness. Plant supersweet varieties 250 feet away from other corn varieties to insure no cross pollination.
If you only have a small space to garden and still want to grow sweet corn try planting it in a raised bed. Select a dwarf, quick maturing variety such as ‘Earlivee’. Fill the raised bed with a mix of topsoil and compost and plant at least 12 corn stalks spaced 8 inches apart. When the tassels form, shake them to insure the pollen falls on the ears so your ears fill in with kernels.
Care and Maintenance
Sweet corn needs a steady supply of nitrogen fertilizer to grow as fast as it does (yes, I swear I can actually see it grow during one of our hot, humid summer days), and produce a good crop. Beside adding compost at planting, add supplemental nitrogen fertilizer, such as alfalfa meal or soybean meal, when corn is knee high and again when it starts to form ears. If your corn leaves are yellow, it could be a sign of nitrogen deficiency.
When the plants are 8-inches tall, hill (mounding up soil) around the plants. Hilling kills weeds and helps support the corn plants so they’re less likely to blow over in a summer thunderstorm. After hilling mulch with straw or untreated grass clippings to preserve soil moisture. Corn that is stressed from lack of water will have narrow leaves and ears missing kernels. Remove any small corn plants or suckers that form at the base of the main plant.
Unfortunately lots of insects, diseases, and animals love corn, too. Corn earworms are small worms that feed on the tips of ears. Simply cut off the end of the ear when harvesting to remove this insect. Corn borers tunnel into corn stalks causing them to topple over. Spray with pyrethrum or spinosad early in the season to prevent this damage. Probably the biggest thief of corn is raccoons. They have an uncanny way of knowing just when your corn is ripe and at night before you want to harvest they come in and devastate a patch. String an electric fence around your corn or cover individual ears with paper bags after pollination to ward them off. Birds have been know to pull newly germinated corn seedlings out of the ground. Cover your patch with a floating row cover until the corn is at least a 3- to 4-inches tall and less appealing to birds. Control diseases such as bacterial wilt, and leaf blight by growing disease resistant varieties.
Most corn varieties produce 1 or 3 ears per stalk. Depending on the variety your corn is ready to pick 60 to 100 days after planting. To determine when to harvest, watch the silks (hairs on the ears). When they turn a dark brown color, pull back the top of the husk a little bit and with your thumb nail squeeze a kernel. If ripe, the liquid should squirt out a milky white color. Immature kernels will be watery while over mature kernels will be tough and have little liquid. With a sharp motion, pull down on the ear to harvest without breaking the stalk.
The three most common types of sweet corn to grow are standard, sugar-enhanced, and supersweet. Some good standard varieties for our region include ‘Earlivee Hybrid’ (yellow), ‘Silver Queen Hybrid’ (white), and ‘Sugar and Gold Hybrid’ (bicolor). Some good sugar-enhanced varieties are ‘Sugar Buns Hybrid’ (yellow), ‘Luscious Hybrid’ (bicolor), ‘Sugar Pearl hybrid’ (white). Some good supersweet varieties are ‘Northern X-tra Sweet Hybrid’ (yellow), ‘X-tra Tender hybrid’ (bicolor), and ‘How A Sweet It Is Hybrid’ (white). An old fashioned variety for our region is ‘Ashworth’ (yellow).
Text excepted from the Northeast Vegetable and Fruit Gardening book.
It was supposed to be knee high by the 4th of July, but more likely it was knee high in water. But with the recent spate of hot, humid weather sweet corn is taking off. If you’re growing your own patch here are a few pests to watch for.
The corn earworm adult moth lays eggs on the silks of corn ears. The eggs hatch and the caterpillar tunnels into the ear tip to eat the silks and kernels. It’s more prevalent on early season than late season corn varieties. You can ignore this pest and simply cut off the tip when you harvest or you can add a few dropperfuls of vegetable oil to the silks when they turn brown to smoother the eggs.
Corn stalk borers are a bit more troublesome. The young larvae feed on corn leaves, tassels and silks causing stalks to break and ears to be damaged. Spray Bacillus thuriengesis kurstaki (AKA dipel or thuricide) or pyrethrum on corn leaves and ears when when start seeing the damage.
Raccoons are probably the biggest reason I don’t grow sweet corn. They have an uncanny ability to know exactly when you’ll be harvesting your corn and come the night before to decimate the crop. While many try scent deterrents such as animal urine and human hair. Some gardeners wrap duct tape around individual ears to protect them. However, the best protection is a good electric fence. Place the wire 6 inches and a second wire 12 inches above the ground. Install the fence before your corn is mature.