When and How to Grow Sweet Corn in the Home Garden
Sweet corn is a signature of summer as much as a juicy watermelon or vine-ripened tomato. The flavor is so much sweeter and fresher closer to picking, making it superior right from our own garden. Garden expert Katherine Rowe explores how to grow sweet corn at home for the best flavor and nutrition.
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Sweet corn is the best “eating” type of corn, and with good reason: it has the highest sugars among its juicy kernels. The range of sweetness differs by variety, but uniformly, the sugary goodness is at its prime when picked fresh at peak readiness. Sweet corn from our own vegetable garden is good enough to eat raw, right from the stalk.
The historic crop is easy to incorporate into the home garden, especially with measures to avoid common problems. As the weather warms, the time for easy sweet corn sowing is here. With a few planting tips for the best foundation, we’ll be on our way to enjoying the sweet rewards on summer evenings.
What is Sweet Corn?
The heritage crop stems from wild grasses that date back 9,000 years. Today, Zea mays is one of the most widely grown crops for its many uses. Some 4,000 years ago, corn (or maize) became a staple in the diet of ancient peoples in Central and South America, who cultivated and shared the kernels.
Each stalk produces one upper ear of corn and smaller secondary ears. In addition to their sweet flavor, the kernels hold antioxidants, vitamins A and C, nutrients like magnesium and potassium, and dietary fiber. Starches that create the sweetness are best closest to picking time; they begin to break down as time increases from stalk to table.
Sweet corn harvest times vary depending on the variety and climate. Ears usually mature in 60 to 100 days, depending on the selection and weather. The key indicator for corn readiness is the silks, the threadlike tassels that appear on the tips of the ears. With a small window for peak harvest, keeping an eye on days to maturity and appearance are important in gauging when to pick.
The Best Growing Conditions
Corn relies on full sun and warmth to develop, benefitting from six or more hours of sunlight daily. It grows best in organically rich, well-draining soils. A neutral to slightly acidic soil with a pH near 6.0-6.5 is ideal, though corn isn’t overly picky as long as there is fertility and good drainage.
Kernels are best direct-sown to avoid transplant disturbance for sensitive roots (and seed-sowing sweet corn is easy). Prepare the planting site by loosening the soil to a depth of ten inches. Amend with compost to add nutrition, aeration, moisture retention, and drainage, especially in clay or sandy types.
Sweet corn needs warm temperatures to germinate and develop. Chilly spring nights can hinder growth and result in fewer cobs. Wait for warm temperatures for planting, where the stalks quickly take off.
Timing the Harvest
Sweet corn is ready to harvest a few weeks after silks develop, which appear a few weeks after planting. There’s a short timeframe to pick for maximum sweetness – often just a few days—and keeping track of the general days to maturity is a guide for harvesting at the right time.
Following the “days to maturity” on the seed packet, count the days from your planting date to mark when to check for harvesting (it’s handy to ask Google how many days it is from your planting date, and add it to your calendar). The silks at the top of the ears indicate readiness. When the threads turn brown, allow two to three weeks for the ears to be fully mature and less in hot weather (more below).
Successional Plantings
Planting a few rounds every few weeks ensures plenty of cobs to enjoy throughout the summer and into early fall. Since stalks produce all at once, or nearly so, staggering the plantings yields multiple harvests. Sow the same variety successively or use different cultivars suited to early, mid, and late-season harvests.
Corn is open-pollinated, which means that if you’re planting more than one variety that ripens simultaneously, the genetics and qualities may cross. Wind and insects travel between stalks, moving around pollen granules between the silks. The subsequent pollination alters the selections. The flavor may not be as sweet, white corn may become yellow, etc. If you’re growing a single variety, there’s no concern over genetic crosses.
When growing multiple varieties, there are a couple of ways to prevent characteristics from crossing. The first is to isolate crops 250 feet apart. In the home garden, a more feasible option is to stagger the plantings to vary maturity times.
The first option (isolation) requires a lot of space. The second one, staggering developing ears, is doable by planting one selection earlier than another or opting for early-, mid-, and late-season distinctions. Allow 14 days between mature yields to prevent cross-pollination.
Growing From Seed
Direct sow kernels in their garden locations for the least stress on young seedlings. In areas with short growing seasons, start corn indoors for transplanting outside as the weather warms. Try to time it so the kernels are only in cell packs for about two weeks before transplanting outside, as the short time frame lessens extensive root development. Opt for soil blocks or biodegradable pots.
Sow kernels one to two weeks after the final frost date. Sweet corn germinates best in soil temperatures above 60°F (16°C) and ideally between 65-90°F (16-35°C). The warmer, the better for these heat-loving crops.
For best pollination, grow the stalks in blocks rather than long, single rows. Sweet corn also grows well in raised beds. Sow them in groups of two to three seeds with a spacing of one foot apart (or according to varietal spacing guidelines). Sow them one to one and a half inches deep.
Thin seedlings when they reach four inches tall by selecting the strongest and clipping the others below the soil level. Clipping, rather than pulling, minimizes root disturbance for the remaining seedlings. Clip them below the soil to prevent regrowth, as they’ll continue to sprout with light exposure.
Irrigation and Fertilizer
Sweet corn needs regular water throughout the growing season. An inch or two of water per week is usually sufficient to support the growing stalks, leafy growth, and cob development. Supplement with irrigation if seasonal rainfall isn’t enough. Moisture is essential after silks appear and as the juicy kernels are developing.
Corn is a heavy feeder, as the sizeable annual crop grows and reproduces in a single season. Fertile soils give the best foundation. To supplement nitrogen, phosphorus, and potassium, topdress with a balanced, organic, slow-release granular fertilizer at sowing. Sidedress (scratch in around the base of the plant) with an additional application four to six weeks after seedlings emerge.
Promote Pollination
Before the silks, tassels that hold pollen emerge from the tops of the ears. The pollen granules are carried by the wind or travel with insects. Each silky strand needs pollination for all kernels to develop, and weak pollination results in missing rows of kernels.
Attract pollinators by interplanting companion plants and flowering annuals and perennials. Nectar and pollen-rich blooms attract beneficial insects that prey on sweet corn pests like corn earworm. Ladybugs, green lacewings, and parasitic wasps feed on the eggs and larvae of the earworm.
To ensure even pollination, you can hand-pollinate sweet corn by shaking the stalks so the tassels disperse the granules, dropping them onto the silks. Alternatively, you can snap off a tassel and brush the silks on up to 10 plants.
Check Regularly
Checking the crop every day or two is helpful once the readiness stage approaches. Peak ripeness lasts only a day or two. Upper ears develop first, secondary follow closely behind, and all are generally ready within two or so days of each other. Look for filled-out tips. Ears that are ready have tender kernels all around the top.
As silks turn brown, allow two to three weeks for the ears to mature fully. In hot weather, they may be ready about 15 days after the silks turn brown. Some varieties take up to 22 days to fully develop from this point. Husks and stalks remain green when silks turn brown and kernels get closer to ripeness.
When to Harvest
Kernels go through developmental stages, including pre-milk, milk, early dough, and dough. At the late dough stage, the kernels are overripe—tough and dry. With the early pre-milk, the juice is clear and not as sweet. The perfect harvest is in the milk stage.
To check for readiness, peel back the husk slightly and poke a kernel. If the juice is milky white, the harvest is ready. The milk stage doesn’t last long and is weather-dependent, accelerating in hot temperatures. In temperatures above 85°F (29°C), the milk phase may last only a day or two.
Harvesting at other stages doesn’t render the ears inedible, but the flavor is less optimal. You may grind the cobs for flour or dry them for seasonal decor. If you leave them in place to linger, they can become wildlife forage for the fall and early winter.
How to Harvest
Pick sweet corn early in the day before the sun warms the kernels. Once separated from the stalk, the sugars begin converting to starches, and heat hastens the process. The conversion results in a less sweet flavor the further out from picking. Extra-sweet and sugar-enhanced cultivars remain sweeter for longer.
To pull the ready ear from the stalk, pull it downward, husk and all. Twist it to snap it loose from the stem. Refrigerate the fresh cobs promptly to slow the sugar-to-starch turnover. This delays the flavor loss for up to a week.
Storage
Refrigerate corn for preservation or freeze it to preserve any excess bounty. Use the frozen kernels for cool-season soups, stews, and breads. The texture of frozen kernels differs from fresh kernels; they’ll be slightly chewier and less plump.
Wash and blanch the corn first for the best preservation. It stops enzymes from deteriorating flavor, texture, and color. Place the cobs in boiling water for two to three minutes, followed by a dip in an ice bath for the same length of time. Cut off the kernels, and follow the flash-freezing steps.
Flash-freezing is quick and easy. Scatter the kernels on a parchment-lined baking sheet and freeze for a couple of hours. Once completely frozen, transfer the kernels to a freezer bag or an airtight container to store and freeze the lot.
Alternatively, cover the kernels with water in an airtight container and freeze them as ice cubes for up to 10 months.
Popular Varieties
To tailor the sweetness level to your taste, explore heirloom and conventional varieties with different intensities. The beautiful coloration also adds diversity to the garden and the plate.
‘Martian Jewels’
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botanical name Zea mays ‘Martian Jewels’ |
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sun requirements Full sun |
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height 6’ |
‘Martian Jewels’ brings aesthetic intrigue in addition to its sweet kernels. It has glowing, pale white kernels against violet-purple husks and cobs. The flavor is delicate and not overly sweet when cooked fresh after harvest.
Leave it a bit longer to mellow for soups and breads and even further for drying and grinding for flour. The colorful ears, dried, also add to autumnal decor later in the season. ‘Martian Jewels’ matures in 80-90 days.
‘Ambrosia’
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botanical name Zea mays ‘Ambrosia’ |
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sun requirements Full sun |
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height 6.5’ |
‘Ambrosia’ is a bicolor, midseason variety with plump, juicy, checkered kernels in creamy white and buttery yellow. With early vigor and disease resistance, the hybrid matures in 75 days.
The hearty, eight-inch ears top tall stalks. Space seeds in groups of 2 at one foot apart to allow for mature size and air circulation. This sugar-enhanced selection becomes the classic sweet corn of summer.
‘Golden Bantam’
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botanical name Zea mays ‘Golden Bantam’ |
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sun requirements Full sun |
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height 5’ |
Introduced by Burpee in 1902, ‘ Golden Bantam’ was the first yellow-kerneled variety to be popular beyond its white corn predecessors. The yellow corn became the variety to beat, with sweet kernels on five-foot stalks.
‘Golden Bantam’ often bears two sturdy ears per stalk. Its classic corn flavor remains when boiled or roasted, and it freezes well on the cob.
‘Golden Bantam’ is an early sweet corn that performs well in cold spring soils. Direct sow it early in the season after the final frost when the soil warms above 60°F (16°C).
