Sweet Corn
(Zea mays)

Cultivars

What can anyone say about corn that someone else has not long ago said better? But with that basic caveat understood, there are yet things to keep in mind. Americans are literally spoon-fed sugar from—again, quite literally—the crib onward. Some noted chef once remarked that each country’s cooking has its characteristic taste: in France, butter; in Italy, tomatoes; and in America, tin. He would have been more nearly accurate to say “in America, sugar.” There is sugar, usually lots of sugar, in virtually everything Americans are sold at the grocery store. So, it is hardly surprising that with that artificial, force-fed taste so widespread there is now lots of sugar in even home-garden vegetables, including—perhaps notably—in corn. There are sweet hybrids, extra-sweet hybrids, super-sweet hybrids, and now even “augmented super-sweet”s (and recall that the original OP (open-pollinated) type was usually called “sweet corn” to begin with).

There remains, however, a not inconsiderable core of corn fanciers who believe that while a little sweetness never hurt corn, and likely helps, enough is enough.

Corn Types: Sweetness

There are several types of corn, and seedsmen’s catalogues too often do not make those distictions clear, so let’s set them forth here. (The terms we use here to designate them are derived from corn genetics.)

su:

The su type of corn is what is meant by such phrases as “that good ol’ time corn!” It is what yet within living memory was the only kind of “sweet corn” grown for table consumption. Its flavor is no doubt fine and distinctly “corny”, but it has a huge problem: quite literally the instant an ear is separated from the stalk, it begins to rapidly convert its sugars to starches—hence the old saying “You walk out to pick corn then run back to the house to cook it.” Mark Twain once suggested, not entirely in jest, that folk set up boiling kettles amidst their cornfields, to avoid the time spent running back to the house. Nowadays, only OP fanatics grows such corn types, and we will disregard them from here on.

se:

The first genetic improvement bred into corn was the se (“sugar-enhanced”) gene, which of course made it (somewhat) sweeter—but also somewhat slowed the sugar-to-starch process, which was a vast improvement. Today, se corns are very popular, and many consider them the only sort worth growing. But, while one no longer needs to more or less literally run from cornfield to stove, it behooves the gardener to move as quickly as reasonably possible in getting the corn cooked or frozen; one seedsman says "retains that sweetness for 3 to 5 days after picking", but we’d try to get it processed the day of picking, or the very next day at latest.

sh:

The next big jump (not everyone would call it an “improvement”) in corn genetics were the sh types (also described as sh2), commonly referred to as “super-sweets”. They are, obviously, a lot sweeter than even se types, and they have much slowed the sugar-to-starch conversion (now you could safely wait a week or two, maybe more) but…they have some drawbacks, too. It is commonly said that: a) supersweets tend to have tougher and thicker skins, which make their kernels less tender and harder to remove from the cob; b) even though supersweet corn will not lose sweetness during shipping, the quality called “creaminess” is often long gone; and c) supersweets don’t tolerate cold well. YMMV, but we will pass on sh types, and suggest that you do too; if you crave sweetness that badly, then for pity’s sake just sprinkle sugar on the ears instead of salt.

triple-sweets:

It starts to get really confusing here: the term "triple-sweet" can mean a further-modified sort of sh2 corn, or it can mean hybrid types, as described next. In any event, take everything we said about sh types and turn the dial up to 11.

sy:

So-called “hybrid” (sy) corn types have kernels that are approximately 75% se and 25% supersweet. They are reported as not growing or storing nearly as well as the sh2 and se varieties. We again pass.

Fedco—a very well-respected seed supplier—said in their 2021 catalogue For decades, Fedco has been a firm proponent of “eating quality” in sweet corn with flavor, texture and kernel depth as our in-house metrics. We’re a “corny” flavor bunch, dismissing sweetness as the sole measure of breeding progress. Until recently, we hadn’t encountered eating excellence in a Supersweet (sh2) variety. Breeders have now balanced the extra-sweetness with tenderness, creaminess and full flavor. With the sh2 gene, conversion of sugar to starch occurs at a much slower rate, so corn always stays sweet long after harvest. In consequence they now carry two Supersweets (Nirvana, a bi-color, and Yellowstone, a yellow, both listed as 75-76 days DTM and each accompanied by encomia about not only quality but productivity. A number of other masjor seedsmen are also offering those types, as well as some others of the same sort (Epiphany, bi-color; and Eden RMN, white.) Those all are listed as 75-76 days. It all sounds exciting, but we’ll wait a season or two for gardener reports to come in.

Sweetness Levels:

To go from qualitative to quantative:

• su: 5% - 10% sugar
• se: 12% - 20% sugar
• sh2: 20% - 30% sugar
• triple-sweet: > 30% sugars

Corn Types: Color

There are three basic sorts: yellow, white, and bi-color (mixed yellow and white kernels). Despite much partisanship, the bottom line appears to be that color does not affect flavor. But that is not to say that it doesn’t affect eating value, for which color (or perhaps parti-color) one prefers probably unconsciously affects our perceptions. For us, it’s yellow corn—anything else just looks like plastic; YMMV.

Selecting a Variety

All the above said, selection of varieties is still not simple. Climate has a large part to play in dealing with this heat-loving vegetable. Our summers here are warm—quite warm—but not long. Corn traditionally is classed in three admittedly vague categories: early, mid-season, and late. We certainly cannot plant late-season corn with any reasonable expectation of success. Regrettably, experience has taught us that even mid-season corn is can be cut off by early temperature drops unless the planting time is exquisitely reckoned. We thus turn to either early types or what one might call “early mid-season” types if we want a fair shot at a crop every year. The difficulties with early corn types are two: first, too many have relatively little flavor, and that not necessarily good; and second, the ears are, not surprisingly, somewhat smaller than with later types.

And even with all that said, it’s still quite a search. Let’s see where we are: we (though perhaps not you) want an se type, all-yellow, and with a projected days-to-maturity (DTM) of not over 80 days but not a runty “early-season” type. So? So we turn to the invaluable Cornell “ Vegetable Varieties for Gardeners” database under yellow corn (se) and look for high-rated types with a DTM of not over 80 and a “stars” rating not under 4.5.

We find this list: Welcome; Miracle; Bodacious; and that, for ratings over 4.5 (actaully for all over 4.0), is it. Next, we look for seed availability. Type “Welcome” seemed unavailable; type “Miracle” can be found, but the few that carry it list it as 82 days or 84 days, longer than the 77 to 80 days the Cornall database shows. So we have winnowed it down to Bodacious, which is quite widely available. Its DTM is 75 days, based on a sampling of 30 seedsmen (25 reported exactly 75 days and only 3, 10%, reported a number over 75 days).

Next, we reviewd gardening forums. Bodacious was frequently mentioned in quite favorable terms. It is also said to be pretty disease-resistant and to tolerate cool temperatures better than most corns. All in all, it looks like a real no-brainer choice (again: given our criteria—se type, yellow, DTM<80 days, high gardener ratings).

Whether one wants treated seed or untreated seed is a personal decision: organic growers cannot use treated seed. “Treated seed” refers to seed that has been dusted with a USDA-approved chemical to help overcome common issues that can affect germination and early plant growth.

Planting

Timing

Corn loves warmth, and will not germinate well or grow well in cool soil or weather. The optimum germination soil temperature is 95°, so obviously we can’t have optimum; but corn will not germinate at all if the soil temperature is below 55° F., and will likely do very poorly if it is below 65°. Waiting for 70° average daytime soil temperatures—if that doesn’t shorten your season to less than 75 to 80 days—is best. Plant corn, like most or all warm-weather crops (such as beans or squash), according your soil thermometer, not your calendar.

Bodacious is listed as 75 days. Our nominal plan is to seed it out somewhere around June 1st (as the thermometer allows) for harvest somewhere around mid-August. But if it is that rarity around here, a cool summer, we’ll just have to wait till the soil is at least at 65°. Fortunately, we have, based on average temperatures, a good couple of weeks of slop at the end of the growing period.

(Very obviously, your garden climate will determine your planting dates, but the numbers we cite should give you a handle on things.)

The Bed

Corn is a very, very heavy feeder and so needs soil that is extremely well-fertilized. (It makes a good follower, in crop rotations, to legumes, which enrich the soil with nitrogen.) Though corn is mainly shallow-rooted, a deep-dug bed is best, especially when using closer spacings. Some gardeners actually grow legumes right in the corn bed, to provide extra nitrogen to the soil as the crops grow. A common choice in such cases is one or another pole bean, planted as the Indians of the southwest did it, so that the vines climb up the corn stalks. Or you could grow a “living mulch” of some leguminous cover crop, such as hairy vetch. At the least, you should provide some sort of organic mulch, say straw, to help keep moisture in the soil and combat weeds.

Planting Out

Corn is invariably direct-seeded; some in cool, damp climates (like Washington State’s coastal “rainyside”) might try seedlings, but corn notoriously does not transplant well, and in most climates there’s no need whatever for transplants. Plant the seed kernels ½ inch deep in cool, moist soils, or 1 to 1½ inches deep in warm, dry soils.

The matter of stalk spacing can be contentious. Many discussions of it are based on plantings in rows, so you have to deal with spacing in rows and spacing between rows. That ignores the fact that because corn is wind-pollinated, it is a really, really good idea to plant it in blocks, rather than separated rows. Deep-bed gardeners always plant blocks anyway, and whether you’re one of them or not (we highly recommend it), you should still try to do corn in blocks that are preferably three or, better yet, four plants wide in each direction.

But the question of spacing, even in block plantings, remains. We will never forget the sight, back in King City, California (in the Salinas Valley), of an empty lot next to a small house, in which lot ten-foot-high corn plants proliferated densely at a spacing that looked like—in drive-bys—6 to 8 inches. We ourselves have grown corn at one-foot spacings with satisfactory results. But it may be that yet-tighter spacings might work well (though we’ll stick with that one foot). The chief consideration is not so much whether the individual stalks will be healthy—with sufficiently rich soil, they’ll be fine—as it is the ears-per-stalk number. You will always get at least one ear per stalk (well, virtually always), and you will rarely if ever get three or more; but it seems common belief that if you give stalks wide spacing, you are likely to get two ears per stalk, whereas if you space them close you will assuredly only get one.

Let’s take a quick and dirty look at this. Assume a block 4' x 4', which is 48" x 48". If we space stalks closely, say at 8", we get a stalk array of 6 x 6, for 36; and if each stalk gives us a single ear, we get 36 ears. Now assume that we instead space them at 16", and at that spacing get two ears per stalk (not likedly, but let’s be generous): then we have a stalk array of 3 x 3, for 9 stalks x 2 ears per stalk, or 18 ears. Which is more, 36 or 18? Get the idea…?

While the example above is an inexact, broad-brush look, it seems clear that spacing out to where you might get two ears per stalk does not look like a wise use of space. That said, we should consequently space the stalks as close as we can without harming their individual health. That could be as little as 6" (but no less) or as much as 12" (but no more). We use 12", but if you’re experimentally minded, you might try 10" or 8" or even 6": it depends in part on the size of the space you have for your block or blocks, as you want the block space to be some integral multiple of the stalk spacing (so for a 48" width, you’d want either 6", 8", or 12").

If you plant several varieties of corn, beware unwanted cross-pollination: “Supersweet varieties pollinated by standard sweet corn, popcorn, or field corn do not develop a high sugar content and are starchy. Cross-pollination between yellow and white sweet-corn varieties of the same type affects only the appearance of the white corn, not the eating quality” (University of Illinois).

Growing

General Principles of Corn-Growing

From the University of Illinois:

Cultivate shallowly to control weeds. Chemical herbicides are not recommended for home gardens. Although corn is a warm-weather crop, lack of water at critical periods can seriously reduce quality and yield. If rainfall is deficient, irrigate thoroughly during emergence of the tassels, silking and maturation of the ears.

Hot, droughty conditions during pollination result in missing kernels, small ears and poor development of the tips of the ears. Side-dress nitrogen fertilizer when the plants are 12 to 18 inches tall.

Some sweet corn varieties produce more side shoots or “suckers” than others. Removing these side shoots is time consuming and does not improve yields.

Each cornstalk should produce at least one large ear. Under good growing conditions (correct spacing; freedom from weeds, insects and disease; and adequate moisture and fertility), many varieties produce a second ear. This second ear is usually smaller and develops later than the first ear.

Sweet corn ears should be picked during the “milk stage” when the kernels are fully formed but not fully mature. This stage occurs about 20 days after the appearance of the first silk strands. The kernels are smooth and plump and the juice in the kernel appears milky when punctured with a thumbnail. Sweet corn remains in the milk stage less than a week. As harvest time approaches, check frequently to make sure that the kernels do not become too mature and doughy. Other signs that indicate when the corn is ready for harvest are drying and browning of the silks, fullness of the tip kernels and firmness of the unhusked ears.

To harvest, snap off the ears by hand with a quick, firm, downward push, twist, and pull. The ears should be eaten, processed or refrigerated as soon as possible. At summer temperatures, the sugar in sweet corn quickly decreases and the starch increases.

Pollination of Corn

Not mentioned in the advice above but crucially important is satisfactory pollination: if you don’t get it, the ears will grow ok but be only partially or hardly at all filled with kernels, which is stupendously disappointing. One normally looks for the wind to pollinate the plants, but giving Mother Nature a little helping hand is never a bad idea. The University of Florida has an illustrated online document titled Home Vegetable Garden Techniques: Hand Pollination of Squash and Corn in Small Gardens (a PDF file) that is helpful. Or, to quote one gardener:

The pollen is at the end of each tassel, not the ones coming out the top that look something like wheat, the ones hanging down. Each of these leads to a kernel of corn. Each needs to catch some pollen from another. What I’ve done is gone from plant to plant, tickling the ends of the tassels with my fingers from plant to plant.

You can also view online videos showing how to hand-pollinate corn; YouTube has quite a collection of corn-pollination videos available. (If you have a YouTube video downloader app, you can sample the ones on line then download the one you find most useful for later, closer review.)

Watering Corn

Corn needs lots and lots of water—particularly just before the appearance of the silk, and a couple weeks after the silk turns brown (which is the kernel-filling stage). Avoid overhead watering: wet tassels and silks may mean wet pollen, hence no pollination, hence no corn. As with many vegetables, regular strong “deep watering” works better than more frequent but more casual watering.

We heartily recommend watering corn by either drip irrigation or, if that proves impractical, with soaker hoses.

Protecting Growing Corn

Corn is relatively shallow-rooted, tall, and heavy: that means it is quite vulnerable to wind damage. We sometimes have truly fierce, steady winds where we are. Our first year, with rather pitiful corn that never produced anything worth mentioning (but neither did anyone else’s around here that year), we had pretty bad wind blowover; more recently, with healthy crops that yielded fairly well, we had just as much wind but no blowdown whatever. With the plants set close together—and thus more mutually supporting—one can try without bracing—but an ounce of prevention is worth a pound of corn (or something like that). Some people like to stake strong rods at the corners of their corn blocks and run twine between them as a sort of support fence, and it can only help.

Keep in mind also that critters love corn, and corn seed, too. Make sure that your seed is very thoroughly protected from both four-legged and winged scavengers; if you use row cover, make sure it is solidly pinned down along every inch of its perimeter, and keep it in place till the growing stalks start to seem constrained by it. Once stalks are fairly well along, birds become less of a problem; and if you keep your entire garden decently fenced, you should be keeping out anything able to attack an entire mature corn stalk (voles aren’t in for this). But check daily for possible incursions, and if you detect any act at once.

As for insect attackers, Dipel is an organic product, basically a Btk spray, that handles many of the insect pests of corn.

Using Corn

Corn freezes well, so you can enjoy your harvest all year round and all year long. As to how best to cook corn, whatever you do don’t boil it. Boiling is a pretty horrible way to treat almost any vegetable, and especially the Queen of Vegetables.

“Other chefs who have sampled the world’s field corns may agree with the grilling expert Steven Raichlen: ‘All corn is better grilled,’ he said.”
    —“What Corn Has Come To: So Sweet, But So What?”, The New York Times

If you haven’t a real grill, oven-roast it.

More

Relevant Links

Besides any links presented above on this page, the following ought to be especially helpful (the web is chock-full of corn-related sites—these are just some highlights):

• Plants For a Future Database: Sweet Corn - tons of data on the vegetable, and links to lots more
• The Kernel - “the Latest Corn Research and Management Information for Farmers and Agricultural Professionals”
• Corny News Compendium - a compendium of numerous articles fro Perdue University on corn growing
• Sweet Corn Growing Tips [archived copy] - that’s the name of the site
• Watch Your Garden Grow - Corn - the University of Illinois site much quoted from up above

Odds and Ends

Note that outside the U.S. “corn” is usually a generic name for feed cereals (usually wheat); in such places, what we grow as “corn” is referred to as maize.

Biology

Corn is a cereal—a grass grown for its seed—from the Gramineae family, which includes essentially all of the world’s cereal crops. More than perhaps any other vegetable, corn has been radically altered by human cultivation from its native form, and indeed could not exist in its modern form without humans to grow it.

History

The ancestral form of today’s corn was a wild grass called teosinte, which was quite a bit different from modern corn: its kernels were small, and not placed close together like kernels on the husked ear of modern corn. Its place of origin is believed to have been the Mexican plateau or the highlands of Guatemala. Fossil pollen grains of teosinte have been found in drill cores of lake sediment beneath Mexico City, which sediments could be as much as 80,000 years old.

Apparently, on teosinte, each individual kernel was covered by its own floral parts as are the kernels of oats and barley, and in consequence the cob readily broke down into small segments (which may have been what allowed teosinte to survive as today’s corn could not in the wild). The husk and cob as we know them today were developed from wild varieties by the native population of the Americas.

From Mexico, corn spread north into the Southwestern United States, and south down the coast to Peru. About a thousand years ago, Indian peoples migrating to the eastern woodlands of present day North America brought corn with them. When Jacques Cartier visited the village of Hochelaga (now Montréal) in 1535, he noted extensive corn fields; Champlain found corn growing in the area of Georgian Bay in 1615. Archeological studies have found that corn was grown near Campbellville, Ontario before A.D. 1200.

Corn was unknown outside the Americas until the first Europeans to land found it and brought back samples.

Envoi

Cooking Corn

The fictional detective Nero Wolfe, portrayed as a world-class gourmet, is quoted so on cooking corn:

“Millions of American women, and some men, commit that outrage [boiling corn] every summer day. They are turning a superb treat into mere provender. Shucked and boiled in water, sweet corn is edible and nutritious; roasted in the husk in the hottest possible oven for forty minutes, shucked at the table, and buttered and salted, nothing else, it is ambrosia. No chef's ingenuity and imagination have ever created a finer dish. American women should themselves be boiled in water.”

One cook who experimented with that method reported “Forty minutes at 500 degrees is the best [another said 550°]. It doesn’t dry out. It’s sweet and perfect. Don’t worry about the cornsilk; it comes easily off the ear after roasting. Aside from how much it heats up the apartment, this is the best thing I’ve ever eaten. I’m pretty much making it every day.”

Note! That recipe means that if you are freezing some of your corn, you must freeze the cobs with the husks still on! That is essential for the recipe to work, as the kernels are essentially steam-cooked by the released moisture within the husks. To freeze, then, peel the husks back—but do not detach them—prior to blanching the cobs; then, after the blanching, cooling, and drying, pull the husks back up before freezer-wrapping the cobs.

Maize Mazes

For reasons whose educing is better left to others, cornfields have assumed a mythic quality in American culture (witness Field of Dreams). A peculiarly popular manifestation of that quality is the corn maze (it’s a pun, too).

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