The Journey of Sweet Corn: From Seed to Table

By Gwen Anderson

Sweet corn, the iconic summer vegetable.  You can hardly drive a mile in the countryside without running into fields’ worth of corn of some kind (and probably not the tasty sweet corn type).  But you know right away what it is, with its tall stalks, long green leaves, and silky ears. Even in the city, farmers park their trucks, beds piled high with the golden goodness, off the shoulder of the highways and in busy parking lots to sell their crop to passersby (but the back of the truck is a hot place for corn, and allows the sugars to quickly convert to starch).  Everyone loves sweet corn, which is exactly why we grow it. Richard has a saying: “Some crops you grow for profit. Some you grow to make friends. We grow corn to make friends.” How do we make friends with sweet corn? By prudently selecting the right varieties, careful planning, vigilantly combating pests, and having an expert harvest crew.  If everything is done right, we will have the best sweet corn ever.

The process starts with selecting the best corn seed.  Like with all lifeforms, genetics plays a vital role in the characteristics that show up in corn.  All types of corn, whether field corn, decorative corn, popcorn, or sweet corn, are the same species: Zea mays.  The genes needed to make corn sweet instead of starchy are recessive genes.  The starchy gene is the dominant gene. Genes come in pairs, one from each “parent.”  If the genes passed down from the “parents” are the same, that is the characteristic that is displayed in the “child.”  However, if the genes in the pair don’t match, it is the dominant gene’s characteristic that is displayed. Take humans for example:  Brown eyes are a dominant trait, blue is recessive. If both parents have blue eyes, they will have children with blue eyes. If one parent has blue eyes and the other has brown eyes, the children could have either brown or blue eyes.  If both parents have brown eyes, the children could still have brown or blue eyes. It really just depends on what kind of genes the parents are carrying.

There are three recessive “sweet genes” in corn: sugary (su), sugary enhanced (se), and supersweet or shrunken-2 (sh2).  Su is the oldest of the sweet corn varieties to have been cultivated. It has around 9% sugar content which quickly converts to starch once it is harvested.  The short shelf life of this sweet corn is traded off for good corn flavor, mild sweetness, and a creamy texture. Se corn has between 16-18% sugar content and has a slower sugar to starch conversion rate than su corn, which means that sweet flavor is more stable.  The kernels on se corn are also extremely tender; so tender they are easily damaged. Sh2 corn has about 35% sugar and has a super slow rate of converting sugar to starch. The kernels are also thick, so it stores well. However, those thick kernels also make for a crunchy eating experience.  But remember how genes come in pairs? It turns out genetics isn’t exactly as cut and dry as recessive and dominant genes, and by mixing the recessive traits we can make new kinds of corn: Synergistic (su and sh2 mix) and Augmented (sh2 and se). Synergistic corn blends the sweetness of sh2 corn with the creamy texture and tenderness of su corn while giving it a long enough shelf life to do some traveling.  Augmented corn does basically the same thing, just with the se corn instead of the su corn.  All these hybrids were created by naturally crossbreeding the corn.  We do not use any GMO altered seeds of any kind, nor do we use seeds that have “seed treatments” that contain various poisons such as neonicotinoids.

With this lesson of genetics under our belts, we pick up a seed catalogue.  Farmer Richard has done plenty of trial and error, and has also learned to trust the advice of our experienced seed rep, Phil Timm.  We buy all of our corn seed from the same company because of the relationship we have built with Phil.  With his help, we try new corn varieties and also have been able to find our favorites: Nirvana, Sweetness, Kickoff, and Awesome.

Sweet corn in early July this year

During the winter, we plan which crops we are going to plant and where.  This helps us decide how much seed we are going to purchase. With the plans made and the seeds purchased, it is a waiting game for the right time to plant.  We normally plant corn, weather permitting, around May 1st.  For the first planting of sweet corn, it is essential to pick a variety that has “cold soil vigor.”  We also wait for the perfect time to plant it: a day with nice, bright sun that will be shining for the next 24 hours.  Depending on the soil temperature, we are able to play around a little with how deep we plant the seeds.  For example, we would plant the seeds more shallow if the soil was still too cool in order for the sun to warm the seeds better and encourage them to germinate. However, this can be risky because birds love corn seeds.  Last year, the red-winged blackbirds found our first shallow planted corn in the field, dug it up and ate a good portion of the crop before it could germinate!

Sweet corn field during harvest time

Another thing we need to keep in mind when we are planting our sweet corn is what kind of sweet corn we are planting.  Because of sweet corn’s complicated genetics, it is important to keep sweet corn isolated from other types of corn; this is even true for different types of sweet corn!  Corn is wind pollinated, so we need to be cognizant of preventing cross-pollination.  It is recommended to keep at least a 250 foot distance between corn varieties that will be tasseling up at the same time to avoid cross-pollination between the varieties. Another option is to time the plantings to ensure at least 14 days between the estimated tassel dates to keep corn from cross-pollinating.  If we follow these guidelines, we are able to keep the true genetics of the variety of corn we plant which is then displayed in the characteristics of the corn we pick.  When Richard took me out to one of our corn fields last week, it was situated in a beautiful field next to our winter squash crop, surrounded by wildlife habitat, forest, and rolling hills. It was picturesque, to be sure, but it was also very far away from any other potential corn fields.

I mentioned the importance of knowing when the corn is going to be “tasseling up,” or getting ready to be pollinated to create the kernels.  The pollen of corn is in the tassels.  Corn takes 65 to 90 days to mature, and that range is broken into 3 different sub-seasons: early varieties (less than 70 days to mature), mid-season varieties (70-84 days to mature), and late varieties (more than 84 days to mature).  If we were going to be planting different types of corn together, we would want to make sure that they were in different sub-seasons. By planting corn from different sub-seasons, we can continue to deliver corn as long as possible throughout corn’s growing season, while also avoiding the potential for cross pollination between the varieties.

Richard explaining how the fake owls work

Earlier I had mentioned how the red-winged blackbirds had found our first crop of corn last year.  Birds are only one of the pests we have to combat when growing sweet corn. We have a couple different tactics we use to try to deter birds, but like all deterrents, they need to be in place before the animals figure out there is tasty corn to be had.  We hang “scare eye” balloons with long silver streamers on poles out in the field. These “scare eyes” work on the same principle that protects moths that camouflage themselves with large eye-like patterns on their wings: big eyes mean big predators. The silver streamers reflect light and move in the wind, also scaring the birds away.  We also have fake owls and hawks posted on the fence lines. These fake birds of prey are solar powered and have moving heads, keeping an ever-vigilant eye on the fields for us and keeping pesky corn eating birds at bay. The fence these sentinels sit on is plastic mesh tied to poles we place in the field that are 6 feet high.  This fence is a deterrent to deer, but again, only if they don’t know what is on the other side of it. Corn is a much tastier treat then grass and leaves, and sweet corn is so much better still than the field corn that is growing elsewhere.  The fence also doesn’t do much to keep raccoons out. So, in addition to the fence, we have an electrical ribbon running through the mesh near the bottom of it to surprise and deter any raccoons who try to pass through the fence.

Richard checking the pheromone trap for earworm moths

Now that we have the critters dealt with, there is one last pest we need to protect our corn from: Earworms.  Earworms are moth larvae that hatch from eggs that are laid on the silks of corn ears. When they hatch, they spend a few days on the silks before they eat their way down into the ear of corn.  To combat the earworms, we use an organic approved Bt spray, a naturally occurring bacteria that is toxic to the earworms. We have pheromone traps set up in the cornfields that attract the moths when they are ready to start laying eggs.  When we have moths in the traps, we know it is time to spray the corn. With the right timing, the newly hatched earworms eat the Bt we’ve applied to the corn silk and die before they can damage the sweet kernels inside.  Again, timing is everything and we only want to spray when necessary.

Richard harvesting sweet corn

With the pests dealt with and the corn crop mature, the next step is harvest.  At one time, we had a mechanical corn harvester. We would run it through the field, harvest all the corn at once, and then need to sort through the corn when we brought it back to the packing shed.  This lead to a lot of corn that would never be ripe and good, thus it was wasted. We decided we were going to go back to hand harvesting the corn. This allows us to pick only the best ears of corn at the right moment, leaving the unripe ears to grow up and become the best that they can be as well.  Every person on our corn harvest team was trained by Farmer Richard on how to look and feel for the best corn in the field. Ripe corn will have nice “shoulders” at the top of the ear, whereas an unripe ear will be pointy. If the corn looks like it has shoulders, the next step it to feel the tip, by where the silk is.  If the tip is soft, it is ready to be picked. If it is still a little stiff, it needs a few more days to let the kernels inside grow up and fill the rest of the ear. If the ear is ready to be picked, you grab the ear and twist it down, making sure you snap off as much of the stalk and leave it behind as you can. If you have too much stalk left on the ear, you’ll have to go back later and break it off before you pack it for shipping.  Once the ear is picked, you place it in your bag and move onto the next one. And all of this happens in a split second!

Sweet corn being iced before being stored in the cooler

When your bag is full, you bring it to the wagon and get ice on it right away.  This is a crucial step because icing the corn and keeping it cold slows down the sugar to starch conversion, and lets you enjoy the corn for a longer time!  When harvest is done for the day, the wagon brings the corn home where we ice it again before putting it in the cooler so it can be completely cooled.  At this point, we have done everything we can to ensure that we have grown the best corn ever. It is now your job to make sure you keep your corn cold before you are ready to use it.  Always store sweet corn in the refrigerator and eat it within a few days of receiving it.

Did we achieve “the best corn ever” this year?  We hope you have enjoyed this article about the iconic summer vegetable and have learned a thing or two about how we bring it to your table.  With all the hard work we put into it, we sure hope we managed to make a few friends along the way by giving you a few sweet ears of our golden goodness this year!

Sweet Corn & The Science Behind the Selection

By Farmer Richard

“Some crops we grow for profit, others, i.e. sweet corn, we grow to make friends.” –Farmer Richard, 1980

The genetics of corn breeding have changed dramatically since I started raising sweet corn in the 70’s.  Even then we sought out the exceptional!  Sweet corn varieties are classified with terms that describe and classify their genetic traits.  Back then, all corn was classified as SU (sugary), but we found that white corn had less pericarp (outer skin on the kernel) which made it much more tender.  ‘Country Gentleman’ was an heirloom white corn with irregular rows, but it was tender, sweet, and had great corn flavor.  While these were superior tasting varieties, all the SU corns had a rapid conversion of sugar-to-starch which shortened the shelf life.  If promptly cooled and iced, you had a few good days, but eating the same day was by far the best!

Then came the SE (sugar enhanced) varieties.  The conversion of sugar-to-starch was much slower and we found bi-color corn to be much more tender, but still the rapid cooling and cold temperature kept the SE corn very sweet for several days.   Next, Sh₂ (shrunken gene) varieties were being produced.  The sugar-to-starch conversion was greatly slowed, but they had a thick pericarp, read “tough and not tender.”  Some newer Sh₂ and SE ‘synergistic’ varieties have managed to achieve most of the desirable characteristics including good corn flavor, sweetness, slow conversion of sugar-to-starch, plus cold soil vigor and a tight husk on top to deter corn earworms from entering the ear.  All of the above improvements have been accomplished with natural breeding.  Unfortunately, in the last 10 years, most conventional sweet corn is now genetically modified to produce the Bt toxin in every part of the plant.  But in addition to killing root worms and earworms it has been devastating to other butterflies, including the Monarch.  Aside from the Bt toxin, GMO corn is also modified to be tolerant to Roundup Weed Killer.  GMO corn is not labeled, so as a consumer you have to ask and trust the answer.  GMO varieties are not allowed for certified organic growers, so if you wish to avoid GMO sweet corn, your best bet is to choose certified organic.  Our overall goal is always to produce “the best corn ever!”  Thus, we continue to carefully choose varieties, plant the seeds in rich organic soil, and cross our fingers for cooperative weather.  But the better the corn, the more wild critters come to try and eat.

Corn behind a fence to keep the critters at bay.

Pest control is quite the ordeal with sweet corn.  We put up an 8 foot high fence for deer.  It works, but we have to check daily for breaches.  The cute little raccoons are more persistent.  It takes two electric wires close to the ground and in place to keep them out before they even get a taste.  We also worry about the birds.  The beautiful red winged black bird plus many other birds love a good ear of corn!  They peck the top off the ear to get to the sweet juicy kernels.  We put up scare eye balloons on tall poles with many shiny streamers that flash in the breeze as well as several life sized hawks and owls that turn their heads from side to side.  We try to make it a scary place for the birds before the birds get a taste!

If we can manage to keep the raccoons and birds out, we aren’t in the clear yet.  There’s the corn earworms, a dusty gray moth that migrates yearly from the south.  I liked the image of large flocks of bats leaving their caves in Texas to intercept and feed on the moths before they can get to us.  But, sadly, the health of the bat populations has been compromised by agricultural chemicals, specifically neonicotinoids, and many are unable to fly high enough to intercept the corn earworm moth.  Thus we are left with a greater number of earworms migrating to the north that we now have to deal with.  Instead of combatting this pest with harmful chemicals, we use a pheromone trap to monitor the earworm moths during their night time visit to the corn field.  We haven’t caught one yet, but we check our traps daily now!  If our timing is good, we can have Bacillus thuringiensis (Bt) available for them to eat when they hatch on the fresh corn silks.  Bt is a naturally occurring bacteria that affects only lepidopteron worms.   Our use of Bt affects only the worms on the corn ears, while GMO corn pollen drifts for miles, spreading the Bt toxin to non-target species, especially the monarch larva feeding on milkweed.

Ok, is the corn ready now?  No, patience.  Check the fence, check the traps, and watch for birds daily.  As the ear fills the tip goes from a point to having “shoulders,” which is the kernels, full to the top.  The last week before harvest, we pick a few ears every day to look and taste.  The difference between a good ear of corn and an excellent ear of corn can be the difference of just a day or two. 

Finally picking day comes!  One of the most skilled jobs on the farm, picking corn is done only by a few very experience pickers, all of whom were trained by me, Farmer Richard.  It takes sharp eyes to see the full shoulders through the husk.  Placing your hand over the top, if you feel a full ear with a soft tip under your hand, you twist down and turn, the ear is off the stalk and into your shoulder bag.  Or if your hand feels a slightly stiff tip and not quite full top, you leave the ear to be picked a few days later.  The decision is made in less than a second and you move to the next ear.

Silvestre returning to the farm with iced corn
from the field.

We average harvesting 100 ears per hour, including packing and icing in the field, before the ears come home to the cooler.  We have four fields of sweet corn this year.  The first early corn was planted only half an inch deep just before a couple of warm sunny days to avoid the colder, deeper soil.  It worked, they germinated, but the birds ate 50% of that shallow planted crop.  This is why there were only a few ears per box last week.  The second crop is abundantly ready this week, but space is limited in the box, so we offered it as a Produce Plus item.   We are happy to have received so many orders for it!  Fresh frozen corn has always been a favorite winter treat of ours.  With all due respect to organic processors, you can do better! 

We have two more promising crops to go, if we can beat the critters to it.  We plan to get as much excellent corn to you as we can manage and hope to make some long-time friends. Please let us know if we reached the status of “best corn ever!”