Why we wait to thin corn plants (‘til 4 inches!)

Information in this post comes from and is inspired by the new book The Resilient Gardener by Carol Deppe.

Corn Seedlings

Some gardeners and farmers don’t thin corn at all. But sowing extra seed ensures a uniform stand of corn (especially important for small plantings) and allows us to select for seedling vigor. Thinning gives us plants with better disease and pest resistance, producing earlier, larger ears. For seed savers, selecting the best plants is essential not just to improving a variety, but also to simply maintaining it.

It’s too easy to put off thinning a stand of corn until the plants are a knee-high jungle, competing for light, water, and other resources. But thinning corn just after the plants emerge isn’t in our best interests as gardeners or seed savers either. Ideally, we wait until the plants are about four inches tall.

Why not simply keep the very first plants to pop up? Because these are not necessarily the first seeds to germinate. Many old-time, open pollinated heirloom corns put more energy into their roots initially, before sending their shoots upward. And we love this about them. It means they have bigger, better established root systems when the tender seedlings become vulnerable above the soil. And if the plants get nibbled on or otherwise set back, they can recover much more easily. If we were to select the first plants to emerge, we’d be selecting against this very useful trait.

Additionally, until the plants are about two inches above the ground, they’re still growing off the food reserves in the seed. And that depends on the size of the kernel – which is mostly determined by its location on the ear and the genetics of the mother plant, not on the seed genes. Once the corn seedlings reach four inches tall, we can compare their vigor based on their individual genetic profiles.

So as much as you may hate to watch those extra corn plants creep ever taller before you ruthlessly tear them from the earth, we trust you’ll do the right thing. Wait until your corn seedlings are four inches tall to accurately choose your most vigorous plants. You’ll be helping keep these old-fashioned varieties as hardy and productive as our forebears bred them to be.

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13 Responses to Why we wait to thin corn plants (‘til 4 inches!)

  1. Jenna says:

    Great article! I’ve been slacking on planting my corn… I need to get on top of that! I’ve been thinking about getting Carol’s book for a while now, I’ve been hearing a lot about it. I need to get on top of that, too!!

  2. Dennis says:

    I planted Stowell’s Evergreen Corn and Black Mexican Corn on the same day, May 16th. as of today, 4 June, the Black Mexican is 3-4 inches tall but the Stowell’s has not come up yet. Should I be concerned about this?

    Thank you

    • Phil says:

      If you are concerned about a round of duds, then it is better to have too many seedlings than too few. I say soak some seeds and plant them soon, and if the first round comes up anyway, you can select the best seedlings from the bunch.

      • Dennis says:

        Round of duds? Non of them came up!

        • Ken says:

          Dennis — could you email us the lot # on the seed packet? Email = gardens (at) southernexposure.com We haven’t heard problems from anyone else about the Stowell’s Evergeen, but it’s always good to check things out. (I’d guess that you just had bad luck with the planting — that happens sometimes — but I’ll do a quick germination test on the corn to make sure, and meanwhile we can send you a free replacement packet.)

          Ken
          inventory guy
          SESE

          • Dennis says:

            Just a follow-up: All the seeds from the replacement package sprouted and are doing well.

            Thank you Ken the SESE Inventory Guy!

  3. Phil says:

    Thank you for the article. This information also seems to highlight how the industrial corn varieties were quickly bred for homozygous traits and irrigation. I am a native farmer who is attempting to adapt my three sisters system to my life here within the united states, where I cannot move around to replenish my soils, and the land has been tilled and eroded to ruin hundreds of years before my birth. this sets limits and new laws in place when it comes to soil building and maintaining ones soils in addition to the seeds. Due to the current ecological fragility, I employ no-chemical, no-gmo, no-input, no-till, no animals or machines, dry farming system, where the hills are mulched with the weeds and grasses of the field for water retention, weed suppression, fertilizers and minerals, and soil protection. when i plant my corn, i over plant, sometimes up to 4 times just in order to produce a single sized crop, and in the process, i have fed my herbivore bugs that are eaten by my predators which then grow in population to suppress more pests. i have the pests doing my seedling trait breeding for me. if my corn does not make it up before the weeds and beans, then it does not have the traits to be corn anymore. due to my specific conditions i have been utilizing this method. if anyone would like to give me suggestions or discuss three sisters further, please feel free to contact me. http://goodmindseeds.wordpress.com

  4. Newbie says:

    Can you re-plant the stalks you pull up from thinning or do you throw them out??? Also how sensative are the roots if you do re-plant?? Is the main plant hurt when you pull the smaller ones away??

    • Paul says:

      You can, technically, but we don’t. Corn just doesn’t transplant very well. We have tried and we know many who have and just haven’t gotten many transplants to survive. That being said, we also know people who have transplanted corn from the garden successfully. If you are to try, do it under ideal conditions: plant your seeds far apart from each other, dig up a big clump of dirt from around the seedling, transplant on a cool overcast day, give them plenty of water before and after, etc. You might look for some advice on a square foot gardening or earth box gardening site. They transplant all sorts of things that most gardeners don’t.

      As for hurting the bigger seedlings when you thin, if your seedlings are closely spaced and you’re trying to transplant you’ll have a hard time getting enough earth up around your transplants without hurting the remaining seedlings. If you’re just thinning, it’s not so dangerous. You can hold down the remainders while you pull out the runts or just cut the runts off at the ground.

      -Paul of SESE

  5. Terina Wakefield says:

    Here’s what I did, before I researched this unfortunately. I gently pulled up the runt seedlings and left the bigger seedling in tact and replanted the runts in a new row and some between the dominant seedlings. Will this work?? Will they just not produce or could they die entirely by transplanting?? I am not sure what to expect, I just did it yesterday. All seedlings are currently 1 foot apart and the rows are 2 feet apart. I also put miracle grow on them to help with the shock. I am interested on what will happen to these little guys.

  6. Paul says:

    Well, all I can really say is: good luck. Corn has very sensitive roots and just doesn’t survive transplanting very well. The other thing is that corn is wind pollinated and needs good pollination to set the very seeds that we eat. So, even if your transplants survive they’ll be set back a bit and will probably miss the pollination boat, as it were, since the bigger seedlings that were left in place might have finished tasseling by then.

    To make thinning a bit more palatable, it helps to remember that your thinned seedlings will not be going to waste as they will decay and their nutrients will return to the bed to nourish the seedlings that you left. It also helps to remember that, in nature, plants produce and disperse thousands of seeds in the hopes that a small fraction of them will germinate and a mere handful of even those will survive and prosper and grow old enough to produce fruits and seeds of their own. Our heavily managed ecosystems (our gardens) have a much higher survival rate but there is no need and not necessarily much virtue in coddling every seed to maturity.

    • Terina says:

      Yep, you’re right! I don’t think they are going to make it. Just after a few days those runts looks pretty terrible. I had 6 corn that stayed in tact and I removed 11 runts from them, hoping to get 17, looks like only 4 maybe 5 are going to make it. Lesson learned! This is my first garden, now I know better! Thank you so much for your advice this has been very informational

  7. Terina says:

    Thought I would update you on my transplanting saga – haha. Well I have to say I really lucked out. Here was are 17 days later and all the corn has not only completly bounced back but some has even sprouted more runts, which I plan on trimming not pulling. But all in all, I couldn’t be more excited, now if they get corn will be a different story. Some are waist high and others knee high, so we will see where this goes.

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