There are as many opinions on what makes a delectable tasting ear of sweet corn as there are silks on that ear. Corn perfection, it seems, is a matter of opinion. There are, however, some tried and true cultural methods for gardeners who wish to seek sweet corn superiority. To discover those you might ask Mack Ehrhardt, of Albert Lea Seed House, what's most important when planting sweet corn and he'll remind you it's warm soil.
"What's the second most important thing?" the aspiring sweet corn gardener might ask the Albert Lea, Minnesota seedsman whose catalog carries some 20 sweet corn varieties for Midwestern gardens and farms.
"Warm soil at planting time," he'll tell the gardener without cracking a grin.
Mack says sweet corn's cold soil predicament is a matter of breeding and seedling vigor. Simply put, compared to its elder relative field corn, sweet corn is a wimp.
"Sweet corn just will not sprout and grow as vigorously in cool soil as field corn," he says. "That's a characteristic field corn breeders have bred for the last 60 years. They want to get the corn out of the ground fast so that farmers can plant early and still have good stands. Even if it gets frozen off it'll come back because the growing point is below the ground."
If an unlucky sweet corn plant poked above ground in weather chilly enough to freeze it too would survive. Its growth tip is also below the soil. But if it's frigid enough to freeze corn plants the soil will likely be below 60°F. That temperature is unfriendly to sweet corn germination and growth.
"In sweet corn the primary thing people have bred for is taste, kernel size, the bicolor trait, sugar enhanced, and super sweet characteristics," Mack says. "Vigor has been at odds with those characteristics."
Early seedling vigor is particularly at odds with corn's current sugary zenith: super sweet corn. Most seed companies suggest planting sweet corn in soil that is 60-75°F. Super Sweets, however, shouldn't be planted until the soil is a toasty 70°F, according to the Harris Seed Catalog from a few years ago. Johnny's Selected Seeds recommended an even warmer 75°F in its 2007 catalog. Catalogs are a great guide for sweet corn culture. Here's the soil temperature recommendation from the 2007 Johnny's catalog:
"Cold soil temperatures risk poor stands. Treated corn seeds will not germinate below 55°F and risk low germination under 60°F. Only treated seeds of good cold-germinating varieties may be sown in 55°F or colder soil in anticipation of warming. Otherwise wait to sow treated seeds until 9:00 a.m. soil temperature is over 55°F. Make first sowings of untreated seeds when soil is warm, at least 65°F."
Note the lawyerly phrase "in anticipation of warming" regarding planting fungicide treated seed. Treated sweet corn seeds do not guarantee early, or vigorous, germination. Only warm soil does. Treated seed that has languished in cold soil may not result in an adequate stand.
Not everybody wants treated seed. Mack Ehrhardt struggled with the to-treat-or-not-to-treat dilemma. He recognized the growing interest in fungicide-free seed, so he bought some untreated Ambrosia sweet corn seed a few years ago. Ambrosia is the company's most popular variety so customers grabbed it up, planted it, and then complained.
"Everybody called and said that seed you sold me didn't grow," he says. "That wasn't true. The germination rate on it was perfectly adequate. It was the same as the treated stuff we were selling but they ignored the planting recommendations."
Mack, being interested in keeping customers, refunded their money. Then he phoned his sweet corn seed supplier and asked a question: What variety has the most early vigor?
"They said that would be a bicolor called Trinity," he says. "The next year we carried untreated Trinity and we've had more success with that. It has more vigor. But still we put warnings in our catalog saying untreated seed must be planted in warm soil."
Interestingly, Johnny's Selected Seeds of Albion, Maine picked up Trinity in 2007 and is promoting it for being vigorous when planted in cool soils.
Albert Lea Seed is struggling with another emerging trend. It's mostly organic gardeners and farmers who have wanted untreated seeds. And in recent years, thanks to the release of the national organic standard, they want certified organic seed. You can, however, say organic seed quicker than you can grow it.
"2002 was the first time we had organic sweet corn and it was pretty much a disaster," Mack recalls. "Our problem was bad germination and contamination with other varieties. Customers were saying some of this corn is four feet tall and some is eight feet tall and some doesn't even have ears on it."
The dilemma is that the firms that have normally grown sweet corn seed are companies that don't know about organic agriculture and the organic agriculture people who want to grow seed don't know anything about sweet corn production. Combining the two disciplines is challenging.
"Growing organic sweet corn seed requires tuition. You will make mistakes that cost you time and money before it works," Mack says. "For instance, every hybrid has a different schedule for when you plant the male and the female. You need that knowledge before you plant. One hybrid I was looking at requires you to plant half the males first. When that has a 1-1/2-inch sprout you plant the rest of the males. Then, when the first males have two leaves on, you plant the females."
Some seed companies have been paying their tuition in the last few years and the quality of certified organic seed is improving.
Sweet corn production may be technical and scientific but sweet corn flavor should be a matter of subjective opinion. Plant breeders have recently made it superficially technical, however.
Some catalogs report that there are three types of sweet corn hybrids. There's normal sugary. That's your basic hybrid. Than there's sugary enhanced. Most catalogs follow the name of a sugary enhanced variety with the letters "se." Then, there are the super sweet varieties followed by the letter "sh." The "sh" stands for the genetic trait that gives these varieties light, shrunken, seeds. These three categories are easy to comprehend. But Albert Lea Seeds has had a variety with an "EH" after it. Mack's not sure what that stands for. Not to be outdone, Johnny's has varieties labeled "se+" and "sh2." Harris labels its "se" and "sh" varieties the Sweet Breed and Sweet Gene trademarks. Recently Johnny's has been carrying something call a "Synergistic." Johnny's describes this as a cross between "se" and "sh" varieties. That sounds a lot like what some people have called a triple cross. Fedco, of Waterville, Maine, had a triple cross sweet corn.
"I don't know what that stands for," C.R. Lawn, of Fedco, said in an interview two years ago. "Maybe it's a cross between a sugary enhanced and a super sweet."
There is no evidence of a Triple Cross in the 2007 catalog but there are a couple of varieties (Luscious, a bicolor corn and a yellow called Honey Treat) that Lawn calls "Triple sweet sugary enhanced hybrids." That sounds like what was previously called a triple cross and what Johnny's calls a "synergistic."
This expanding choice and shifting nomenclature caused confusion and disarray among the normally agreeable sweet corn taste testers at Fedco a few years ago, Lawn said.
"We usually trial a dozen varieties and the last two years we haven't been able to agree on anything," he said. "This year eight people took part in the tasting. We had the gamut of palettes but no agreement."
The gamut at Fedco agrees they are seeking to get away from the trend toward candy in corn and toward more "corniness." But how is corniness identified?
"You'll know it when you taste it!" Lawn exclaims.
Not exactly.
"This year I liked Double Play," Lawn said. "I thought it was corny but they didn't. I pretty much liked Providence, too."
Neither variety had enough votes to make it to the catalog. As a committee of one, however, Lawn also recommends Burgundy Delight, a bicolor, and Platinum Lady, a white variety. Intrepid is a yellow variety that he says also balances sugar content with corniness.
Then there's Golden Bantam, an open pollinated variety. Both Fedco and Albert Lea Seeds carry it.
"You now own the sweetest and richest corn ever known," wrote New York seed grower E.L. Coy when he sent two quarts of Golden Bantam seed to Burpee's 103 years ago. Golden Bantam went on to become the standard for sweetness until the hybridizing boom began 50 years later.
Golden Bantam may, or may not, have been the inspiration for Minnesota poet David Bengtson's poem "Grandpa Brags About His Corn" in his book What Calls Us. The poet, then a boy, recounts sitting around a picnic table awaiting sweet corn that his grandfather has fresh picked. It is so sweet it will be just like desert, the grandfather claims. When David's grandmother brings out the steaming kettle of corn the family is expectant:
She lowers the corn to the table next to Grandpa, who smiles
As she forks out one ear at a time, as the plates are passed.
As we butter and salt the ears, then bring them to our lips
And begin to chew the toughest corn we have ever eaten,
Rows of rubber kernels, chew the golden seeds into grist.
And now our eyes dart about, to each other, to Grandpa
For we know we must eat all the ears in the kettle
To honor the one who smiles at our buttery faces, at how
Sweet and tender the corn he feeds his cows is.
The heirloom sweet corn varieties don't hold their sugar like the latest sugary enhanced varieties. They go out of the milk stage, to starch, quickly. David's grandfather's corn may have been marvelous a day earlier. The other possibility is that his grandfather's palette was mired in the 19th century. C.R. Lawn says he tried growing a sweet corn from that century called Howling Mob.
"I found nothing to howl about," he writes in the 2007 catalog.
"Some people like the really super sweet corn with the small delicate kernels," Mack Ehrhardt says. "But some people, like my dad, would much rather have sweet corn a little closer to field corn, frankly. A little less sweet and with bigger kernels. There are people who prefer varieties like Golden Bantam because they grew up on it or that's what sweet corn is to them."
10 sweet corn culture tips
- Plant late for good stands. Or, if you have space, plant every six to seven days until mid-June. Make your first planting at apple blossom time.
- One corn plant can produce 18 million grains of pollen. That pollen is moved by the breezes. Corn needs neighbors for pollination. Seed catalogues recommend planting rows 36 inches apart. In a small garden that's too wide. Particularly since corn should be thinned to one foot apart in rows. If you plant in hills you can plant six to eight plants in a round space 12 to 16 inches in diameter. In our garden we plant a row, then leave a space of eight inches, and then plant another row. Then there's a 30 inch aisle and another row. Using plenty of compost we plant three rows like this and maximize our space.
- Plant your seeds one inch deep, in well-composted soil, and spread the seeds thicker than suggested-perhaps two or three inches apart. Then thin them, if necessary, when they are a few inches high, to one foot apart. You'll get a guaranteed stand this way.
- Seed size varies from variety to variety. Johnny's Seeds says there are an average of 150 seeds in a one-ounce packet. Super sweet seeds are lighter with closer to 250 seeds in an ounce.
- Corn needs lots of fertility. Rodney Hunt, at Albert Lea Seeds, suggests having the University Extension service test your soil to find out what your garden needs.
- Rodney sidedresses his one-foot corn plants with blood and bone meal. C.R. Lawn sidedresses with alfalfa meal.
- The maturity date on varieties is best used as a comparison between varieties. A 75-day variety planted at the same time as an 81-day variety will probably have corn first. Exactly how long it takes to mature depends on when you plant it and how warm the season is.
- Plant an early variety in warm soil for early corn. We've had early good luck, but small ears, with Early Sunglow from Nichol's Garden seed.
- Johnny's says that corn is ready to harvest 18 to 24 days after the silk first shows. The kernels will be full and milky when the silk turns brown. We peel the husks back a bit and look at an ear. If we guessed wrong we fold the husks back for a few more days.
- Try and find varieties whose germination rate has been cold tested. Cold testing tests germination under the cool temperatures found in spring soil. Both Fedco and Johnny's say they cold test sweet corn seed.
