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Growing a Garden Delicacy: Sweet Corn
November 1, 2018

Once upon a time, I used to grow 2-4 acres of sweet corn each summer for roadside sales. Since our farming years, growing good sweet corn has proved to be a bit more challenging. Dry seasons and deer and raccoon predation have made our annual sweet corn production an iffy crop. That's probably why I've avoided writing a how-to article about sweet corn until now. With these experiences in mind, I'll try to describe how we grow good sweet corn.

Sweet corn is a heavy feeder, so growing it in the best soil you have is a good idea. But with enough fertilizer, one can grow very good corn on pretty lousy soil, as evidenced by our success over the years growing it in the heavy clay soil of our East Garden plot.

The most common way to grow sweet corn is to direct seed it in at least four rows about 36" apart. The thirty-six inch row width isn't a hard fast rule, but supposedly is what farmers estimated as the width of their draft horses to pass through the corn when cultivating it. The four row minimum is to ensure good pollination. One can play a bit with both of those figures, but they are also pretty tried and true.

Depending on the varieties of sweet corn to be seeded, soil temperatures should be at least 55° F before planting. Since we grow mostly sh² supersweet hybrids that germinate poorly in cool soil, we wait until the soil has warmed a good bit more before seeding (more like 65° F).

Before planting corn, ones ground should be tilled or hoed to make a good seed bed. If the sweet corn patch needs to be limed and/or fertilized, broadcasting them before tilling works well, although lime takes some time to sweeten the soil. If your ground is around pH 6.5-6.8, it should be okay without any lime. While fall liming gives it time to work in the soil, ground limestone (as opposed to granulated) can give a fairly quick response in the spring.

Broadcasting fertilizer over the sweet corn area really isn't essential in good soil, as one can band commercial fertilizer along the rows when cultivating the corn for weed control. We usually broadcast some 12-12-12 fertilizer before tilling and planting and later band a little more beside the rows. But we grow our sweet corn in an old field that has challenged soil.

I now use a pull-type rototiller to work up our sweet corn patch each year in our somewhat large East Garden plot. In the past, I have used both front and rear tine tillers to do the same job. I still use our twenty-four year old rear tine tiller for cultivation once the corn is up.

Once the ground is prepared, it's pretty easy to mark ones rows with wooden row marker stakes. I buy bundles of cheap wood landscape stakes every few years at a home improvement store. I again space my rows thirty-six inches apart, marking each end of the row with a wooden stake hammered into the ground. Depending on the width of ones tiller for cultivation, rows could be spaced 24-30".

I string nylon twine down the rows, tying it to the row marker stakes. I find I can't plant a straight line anymore without some kind of aid. Then I use a garden hoe to make a furrow along the stringed row. The depth of the furrow often depends on soil type and moisture. If the soil is fairly moist or rain is imminent, one can plant sweet corn seed just an inch or so deep, especially in good soil. One has to be careful not to get the seed in too shallow, as birds like to feast on the seed. In dryer conditions or sandy soils, one can put the seed two to three inches deep, with three inches being about the limit.

With a furrow opened, I space our seed eight to twelve inches apart. One can use a closer spacing, but the longer spacing seems to produce larger ears of corn. I use a garden rake to pull soil back over the seed in the furrow. I then go back and use the head of the rake (or a hoe) to firm the soil over the seed. Like most seeds, sweet corn seed needs good soil-to-seed contact to germinate well.

I often start some extra sweet corn plants in deep inserts at planting time. By the time the plants are big enough for transplanting, I can tell where there are bare spots in my rows that need to be filled in. One can also fill in bare spots in a planting by direct seeding a short season sweet corn.

Care

As ones sweet corn emerges, surely so will weeds. Our first weed control is with a scuffle hoe along the edges of the planted rows. Weeds actually in the row that can't be scuffled need to be pulled by hand. As soon as the corn plants reach eight to twelve inches tall, I cultivate with our walking tiller with one side shield up to throw dirt into the row of corn to bury any emerging weeds. I repeat such tillings as needed, soil moisture conditions permitting. When the corn is around eighteen inches tall, I sidedress the rows with balanced fertilizer (usually 12-12-12) and work it into the soil with the walking tiller, a standard hoe, or a scuffle hoe.

I'd love to say that we always keep our corn rows weed free, but it would be a lie. Damp weather and soil conditions often prevent tilling for weed control at optimal times. In those years, we just do the best we can.

Deer absolutely love tender, young, sweet corn plants. They'll also gladly dine on sweet potato and broccoli if allowed. In the year when my gardening was severely limited by a hip replacement, I transplanted four rows of sweet corn in a tight 12"x12" grid in our main garden. The corn grew well...but it was also next to a corn field. When the plants were just putting on ears, deer came through the tall corn without attracting our dogs' attention and ate every tassel and ear of corn the plants had put on!

We've tried lots of deer deterrents over the years with varying success. At one time, our five dog alarm system kept deer and visitors at bay. Now down to three smaller and much less aggressive dogs, we have to rely on other means.

An option I've resisted is putting an electric fence around our sweet corn. Fence chargers and supplies are expensive. Keeping grass and weeds from shorting out the fencing takes a lot of mowing and weedeating. Trust me, I know. Having used hot wires to contain our hogs and cattle during my farming years, I really hate working with electric fences. But they do work.

Commercial options we've used with some limited success include Nite Guard Solar Predator Control Lights and Sweeney's Deer Repellent Stations. The Nite Guard lights need to be moved around frequently, but the deer (and raccoons) eventually figure out that they're just a bluff. The Sweeney's Stations did keep deer away from our newly planted sweet corn, but failed later on in the season. They are, however, excellent for keeping deer from trimming off the tops of ones sweet potato plants.

I'm not sure if anyone actually bathes with it, but Irish Spring bar soap cut into small pieces scattered along ones corn rows actually does deter deer! It's not 100% effective, but it does provide some protection.

Our best protection from deer in our sweet corn came from a now discontinued product, Not Tonight, Deer. The excellent commercial product went off the market several years ago, and we'd been at a loss until a few years ago to find an equally effective product. The old product package of the nasty smelling stuff listed rotten eggs and white pepper as the main ingredients.

I made two batches of our brew. I mixed together eighteen beaten eggs, white pepper, and habanera sauce. One batch got a quart of buttermilk, while a second got water added. I strained the mixture with some more water into two old gallon jugs and set them outside in the sun for a couple of weeks to cure (rot). Even though the ingredients of the commercial Not Tonight Deer were rotten eggs and white pepper, I added the other stuff from some online recipes.

When applying the stuff about every five days, I strained it again into a hand sprayer with more water. I used about a cup of the mix with water added to make a gallon. Our stuff smelled (and presumably tasted) just as awful as the commercial product used to. It effectively protected our sweet corn from the deer, but not so much with raccoons. Our answers for raccoon damage beyond the dogs and commercial products named above have been to grow our sweet corn as far away from the nature preserve next to our East Garden as possible...and to grow enough corn for both the raccoons and us.

Sweet Corn Diseases

A Clemson factsheet on Sweet Corn Diseases begins, "Sweet corn is seldom seriously damaged by diseases in the home garden." With one notable exception, we've found the Clemson statement to match both our commercial farming and home garden experience.

The Clemson page goes on to add the following sage advice before listing a number of sweet corn diseases that we've been fortunate enough to avoid.

• Use commercially grown certified and treated seed to improve stands.
• Plant corn when the soil temperature is above 55 °F to reduce most seedling rots.
• Keep the garden free of nearby weeds, which can harbor viruses.
• Remove smutted corn ears promptly from the stalks and garden area.
• Remove corn plant debris after harvest to reduce diseases caused by rusts and corn smut. [My added emphasis]

I'll let you peruse the Clemson factsheet for other sweet corn diseases, but have to elaborate on corn smut. We quit growing sweet corn in our main garden because we'd let corn smut get away from us and infest the soil there. We only resumed trying to grow sweet corn when the farm renter of a small field next to us let us use part of it for growing corn, melons, and other space hogs. Since the field had sat fallow for several years, there wasn't much chance of viable smut spores being in the soil. Of course, smut eventually blew in.

As far as I know, there are no chemical controls for corn smut. That's part of what makes it a bane of growing sweet corn. But corn smut can be controlled with a little (er, maybe more than a little) effort.

We regularly walk our rows of sweet corn looking for any signs of corn smut. It may appear at the base of a corn plant, on its leaves, in its ears, or on the tassels. Sometimes an unusually enlarged ear of corn will hide the corn smut within it.

When we see smut, we carefully cut it out, usually removing the whole corn stalk. One has to be very gentle in doing so, as infections of smut like the ones shown below can burst when knocked around, spreading the corn smut spores everywhere. It's best to bag smut infested stalks and let ones trash route take them away. I have, on occasion, put infected stalks on a compost pile, but only when I have lots of grass clippings to cover them with.

In the first two photos above, damage has already been done, as the smut has erupted and spread. Again, let me caution you about handling smut as shown in the third photo above, as it can seemingly explode when jarred. It's a nasty experience.

Insect Pests

There are many insects that like to feed on various parts of corn plants causing varying levels of damage to ones crop. Cutworms, maggots, rootworms, wireworms, aphids, various beetles, earworms, armyworms, and corn borers can all cause problems in sweet corn plantings. Fortunately, one usually has to deal with one or two of these insect pests in various areas of the United States. I've underlined the insect pests we normally deal with.

For us, corn borers and earworms cause the most damage to ears of our sweet corn. We've had success in controlling such pests by spraying mineral oil on the silks of our ears of corn. Of course, corn borers will go right through the wrapper of an ear of corn at times. Japanese Beetles also are prevalent in our area, but mainly feed on the corn tassels. Since honeybees often visit the tassels and silks for pollen, we don't spray insecticides on them.

Products containing the organic, Bacillus thuringiensis (Thuricide and Dipel), can help control some insects. But a San Francisco Chronicle article notes that it is "only beneficial in killing corn pests in a caterpillar stage; the caterpillar must ingest it for the bacteria to work."

Rather than just cut and paste the hard work of others, I'll list and link to some excellent online articles I found on insect control in sweet corn. Note that I've omitted postings from chemical companies.

• Clemson Cooperative Extension: Insect Pests on Sweet Corn by Randall P. Griffin
• San Francisco Chronicle: How to Keep Bugs off Corn by Lori Lapierre
• UMass Extension: Sweet Corn Insect Management Field Scouting Guide by Ruth Hazzard, Amanda Brown, and Pam Westgate

Harvest

Knowing when to pick ones sweet corn isn't all that difficult. Days-to-maturity figures of various varieties can guide one on when to start looking to harvest. But those numbers are only guides. Sweet corn can come in a week early or a week late, based on weather conditions through the season. Supersweet sweet corns are a bit more forgiving in picking times, as they can stay good for a period of up to ten days without losing a lot of quality.

I begin gently pulling down the top of ears a week or so before the days-to-maturity figures suggest ripeness. Popping a kernel with ones thumbnail can reveal how far along the corn is. If the popped kernel exudes a milky substance, it's ready to pick. We also pick by the appearance of the corn silks. When they're brown, the corn is usually ready to pick. Kernels with pointy tips indicate underripe corn.

And corn ripeness can vary by ones tastes. An old friend during my farming years liked his sweet corn when the kernels were terribly underripe with points on them! I'd consider such sweet corn hard and inedible, but that's what he liked. (Sorry, Vence!)

Note that when dented kernels are visible, you've waited too long to pick. A few dented kernels aren't sufficient cause for us to cull an ear, but we do cut out such kernels when freezing our sweet corn.

When we pick after determining most of the first ears are ready, we just go down the row snapping the ears downward to detach them from the stalk. I usually take our garden cart down the row with me to hold the ears. In our farming years when we were picking 2-4 acres of sweet corn (not all in one day), we used shoulder strap bags to hold the picked ears, later dumping them into a wagon attached to our farm tractor. (We only had one tractor, as we were very small farmers.)

Some corn plants will mature a second ear of corn about ten days after the main ear on the stalk is ready. Those ears are usually smaller than the first ears, but the corn can be just as tasty. When we were farming, we often fed the usually smaller second ears to our calves who absolutely loved them. Now, we harvest and gladly freeze such ears.

I'll get around to putting up sweet corn a little later, but should mention here that using or freezing harvested sweet corn should be done as soon as possible after harvest. Even with supersweet varieties, sweet corn begins to convert its sugar content to starch after picking, reducing the good flavor of the corn. This is especially true for open pollinated and old hybrid varieties like Silver Queen.

The Spruce has a nice page on How and When to Pick Sweet Corn by Lauren Arcuri.

Cleanup

Because corn pests and diseases can easily carry over to future crops, we're pretty invested in cleaning up previous years crops. I chop off our corn stalks at their base and compost them. If I can get the tough roots out, they go onto our burn pile, as they don't decay very quickly. Note that a good corn knife makes quick work of cutting down and chopping up corn stalks.

Our sweet corn patches get tilled fairly soon after removing the stalks. Roots not out of the ground can make the tilling interesting. Once the area is cleared, I usually replant it to a buckwheat cover/smother crop, which eventually gets turned under to improve the soil. In some years, we've followed our sweet corn with fall brassicas, as the timing seems to work out well for us.

Note that we only grow sweet corn on the same ground once in four years. Not everyone can rotate crops as we can in our East Garden plot. One should avoid growing corn on the same ground two years in a row, with a three year gap being even better.

Sweet Corn Variety Selection

Most sweet corn seed on the market today is adapted for a wide range of growing conditions. Recommendations from gardening friends in ones area or simple trial and error can lead one to varieties that grow well in your area and suit your tastes in sweet corn.

When you select sweet corn seed, you have a choice of yellow, white, or bicolor corn, each having its own flavor and texture. There are generally short, medium, and full season varieties, with the shorter season ones producing somewhat smaller ears a week or so before full season corns.

Today's sweet corn seed is available in both open pollinated and hybrid varieties, with the hybrids gaining the favor of most gardeners over the last fifty years. Amongst the hybrids, there are regular hybrids and supersweets (sh²), sugary enhanced (se), synergistic (sh² + se), and probably a type or two more that have been released since my fingers typed out this how-to. The hybrids all require isolation from each other. In other words, it's not good to grow them side-by-side with varieties not of their type.

Isolation

One can isolate corn varieties by time, distance, or both. Isolation by time is a little tricky. One has to get the corns to tassel, silk, and pollinate at different times. We achieve this method by starting transplants for varieties we don't want to pollinate our sh² corns. By the time our sh² varieties silk, the transplant varieties are no longer shedding pollen.

Far easier if you have the space is isolating corns by distance. Corn pollen can travel on the wind, so at least twenty-five feet should be the minimun distance one grows different types of sweet corns. For real purity such as for commercial sweet corn, two hundred feet of separation is recommended.

For our 2019 sweet corn, I started transplants of the old favorite white hybrid, Silver Queen, and a relatively new open source, open pollinated bicolor,Who Gets Kissed, weeks before I direct seeded our usual bunch of sh² varieties. That gave them quite a head start on the sh²s. The Who Gets Kissed is a considerably earlier variety than Silver Queen, so they shouldn't cross too much with each other.

Not quite sure of my isolation plan, I also planted the varieties to be isolated at opposite ends of our eighty foot long East Garden plot. Besides isolation by time, the isolated varieties had fifty feet of melons between them.

Area raccoons will probably like my planting plan, giving them two of their favorites side-by-side.

Garden seed catalogs offer a far better selection of sweet corn varieties than seed racks do. Most seed catalogs are free for the asking. See our page of Recommended Seed Suppliers for links to request seed catalogs.

We've standardized our plantings for years using the sh² supersweets. That's not a total endorsement of that type, but it's what we've grown successfully since our farming years forty years ago. Because sh² varieties, and for that matter, almost all supersweets have to be isolated from other types of corn to produce the sweetest and most tender corn, we've stayed with sh² varieties almost exclusively...

...Almost exclusively, as we've experimented in recent years isolating our corn by time. We have no good way to leave several hundred feet between supersweet and other corn varieties, but we've tried transplanting some early varieties so that they will shed their pollen a week or so before our supersweets begin to pollinate.

I'd share some of our favorite sweet corn varieties here, but we've run into some problems. Most of our favorites have been discontinued, a problem with hybrids of any vegetable. We also ran into some serious germination problems from the supplier of most of our supersweets. I ended up having to do extensive germination tests on our sweet corn seed in 2018 to determine what was plantable. Then, as it turned out, I tore up my knees in April and May. We grew no sweet corn (or melons, yellow squash, or potatoes) in 2018.

One of my pet peeves with seed companies has long been them selling old seed. Government regulations currently allow them to do so if the seed meets certain germination thresholds. But stuff happens and we received some sweet corn seed in 2018 that had the same lot number as some we'd bought in 2014. Our seed that had been in frozen storage germinated well, while the supposedly "fresh" seed didn't germinate well at all. The seller had problems with other seed types, eventually admitting that they had a problem with their germination testing records.

Freezing Sweet Corn

Some of my earliest and fondest childhood memories are of days when our extended family gathered at Grandpa and Grandma Tyler's house to pick and freeze sweet corn. The corn got picked early in the day. Then everyone, even five year old grandchildren like myself, were assigned jobs in the shucking, blanching, cutting corn off the cob, bagging, and freezing of the corn.

After harvest, sweet corn should be processed as soon as possible, as it loses sweetness by the hour after picking. We try to shuck and silk our ears, blanch them, cut the corn off the cob, and freeze the corn all in one day. On occasion, the corn may sit on the back porch overnight, but no longer.

Interestingly, just a few days after the two photos above were taken and the corn processed and frozen, we did it again!

After shucking and silking, it is important to cut out any bad spots in the corn. Insect damaged kernels, brown or dented kernels, can spoil ones frozen harvest. I also cut off immature ends of the corn.

The corn gets blanched for around five minutes, cooled a little, and cut off the cob. We bag the corn in Ziplock freezer bags. We try to freeze two, one gallon bags of corn for family dinners, one for Thanksgiving and the other for Christmas. We used to put up the rest in quart freezer bags. With our children grown and out of the house, we now use pint bags to freeze most of our corn.

• University of Minnesota Extension: Freezing sweet corn: whole kernels by Deb Botzek-Linn and Suzanne Driessen
• National Center for Home Food Preservation: Freezing Corn revised by Elizabeth L. Andress and Judy A. Harrison

"War Stories"

During our farming and sweet corn roadsiding years, I rewarded our two sons for their enforced field work by letting them choose a couple of days each week where they got to keep the gross receipts of our sweet corn sales. Both smart guys, they usually chose the weekends as "their days." And working our sweet corn in 100° F plus temperatures was really tough work.

When we were farming, growing sweet corn involved discing the field(s), loading up our old John Deere four-row planter with seed, fertilizer, and herbicide, and having at it. We put down lots of 12-12-12 fertilizer beside the rows in our most fertile fields instead of having fertilizer spread over the whole field. And while we used granular Lasso herbicide in a fourteen inch band over the rows, we later cultivated our sweet corn for weed control.

I'm finishing this how-to after a summer when we couldn't grow sweet corn. I messed up my knees early on in the season, tearing the meniscus cartilage in both of them. Other than our early transplanted pumpkins, butternuts, and some tomatoes and peppers, our East Garden lay fallow in 2018. I started this how-to two years ago, but was repeatedly daunted by the task until I decided to just tell how we grow our sweet corn.

Due to injuries and predator damage, sweet corn has been a hit or miss crop for us. It shouldn't be, but there were the years when I had elbow and hip surgery and tore the cartilage in my knees, and others when deer and raccoons destroyed our crop. One summer, I was lucky to find an ear and a half of good sweet corn after poor growing conditions and deer and raccoon damage took most of the crop. That summer, my wife, a granddaughter, and I each feasted on our total harvest, a half ear each!

But growing sweet corn is deeply ingrained in who I am. I guess I have Grandpa Tyler to thank for that.

From Steve Wood, the at Senior Gardening