My USDA obtained flour corn grex has nitrogen fixing individuals I’m working on making more dominant in the population, and it occurred to me that this would be beneficial to introduce into my sweet corn grex as well. I’m considering just planting everything together, to separate out at a later date when I’m satisfied with the expression of these arial roots. Does anyone have any advice or relevant experience separating sweet corn from a population to grow separately? If I’m not mistaken, the expresion of the sweet kernel is homozygous recessive? I don’t really have a problem with it lingering in my flour corn so I’m not concerned about that.
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If I’m remembering correctly, sweet corn kernels crinkle up and flour corn kernels stay smooth and rounded, and the seed coatings actually show the phenotype of the seed (unlike most species!). So in theory, that should make it easier than with most species to separate the right seeds into the right landraces later.
Someone who’s more of a corn expert than I am, can you let me know if I’m remembering correctly?
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That’s correct, sweet corn kernels are wrinkled and a bit shrunken when dry, flour kernels are not. Without getting into the genetics of it, after letting the two mix you can just separate them back apart by looks. Other traits may still be mixed up, but the kernel type (over time) will mostly become consistent again.
One thing to be aware of is a kernel can be viable for seed without being completely matured. If a flour kernel is not completely mature before drying down, it may wrinkle up and look like a sweet kernel.
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I didn’t know that flour corn kernels could look like sweet corn kernels if they’re dried a bit immature. That’s neat to know! 
I’ve heard flour corn kernels can taste like sweet corn if they’re harvested immature at just the right stage. Is that the stage?
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Some minor traits exist that make sweet corn better tasting and more tender. If you mix in flour corn, those minor traits might cause the mouth feel to go down a bit. No problem if you taste each cob before saving seeds.
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I don’t know how exactly to describe the stage but yes flour corn can taste like candy eaten raw off the stalk at what might be described as at a very immature stage. My grandfather was not all that thrilled about it when I discovered that. I think all corn has that stage, before the sugar starts converting to starch. That sweet stage may be measured in days, or maybe even hours.
Sweet genes delay or prevent that conversion, so it stays sweet much longer. It also prevents the kernel from filling with starch which is why the kernels shrink and wrinkle when they dry. And its why sweet corn is more prone to disease and the like at germination, part of the food reserve for the sprout is missing.
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I can’t taste sweet corn before saving seed. In my environment opening an ear of corn before harvest to eat or at seed maturity results in mold and insects destroying the rest. It hasn’t been a big issue though in selecting good seed.
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I haven’t tried with popcorn but I’ve tried flint, flour, and dent in the milk stage and all can be pretty sweet. Some more than others I’ve noticed. When I used to grow Painted Mountain I would eat half as a “green corn” as many indigenous groups would call it. I currently live a couple hours from mesquakee land and they preserve a lot of their flint corn in this stage by removing from the cob and drying.
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Ha ha ha ha! Did your grandfather not get as much flour corn to harvest after you discovered that? 
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Corn seeds become viable about a week before most people would pick it for the fresh-eating stage. I pick sweet corn for seed about 2-3 weeks after the fresh-eating stage. I taste it at that stage. Even though the best-by date passed weeks ago, it still gives me a good sense of how the cobs would have tasted earlier in their life-cycle. They exhibit a lot of diversity in flavor and texture even weeks after optimal eating date.
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I don’t think I put a serious dent in the harvest, maybe he didn’t see it that way as I did eat my fill on more than one occasion. I never knew why, a day or two later it was gooey and chewy and didn’t taste as good anymore. I also discovered that if you yank the tassel out of a corn stalk just right you get a four- or five-inch section from inside the whirl that is yellow or white, it is very juicy and sweet. I couldn’t reach them or sometimes even the ears without bending the stalk and sometimes they broke. I don’t think he liked seeing that, but his reaction seemed mostly just for show.
That sounds like a good practice, especially for shorter seasons. Depending on the season and when I planted, I have thirty to fifty more frost free days than you and the tail end is usually the direst. I like, if possible, to leave it until the husks are dry and tan and the seeds are hard. I think that makes for a healthier seed and a stronger sprout the next year. Even then there is a bit of sweetness in some kernels. SU corn when fully dried like that has wrinkles in the pericarp but is barely shrunken at all. SE corn like that is still shrunken or “puckered” but not quite as much so. The two biggest issues for me that interfere with letting it dry completely on the stalk is space, I may what to plant something else, and squirrels which can evade all my defenses, except for traps and bullets, but those are not my favorite things to do
There is an old heirloom sweet corn called Aunt Mary’s. It is the finest corn I’ve ever tasted. If I had space and energy, I would grow it and keep it pure. It’s prime window for fresh eating is a day or two tops and have the water boiling or the grill hot before you pick it. That’s actually fine with me because I consider sweet corn more as a summertime treat than anything else. I crossed it to a white early season F1 se, called Spring Snow and another white F1 who’s name I’ve forgotten.
Aunt Mary’s supposedly originated in Ohio and was primo when the commercial canning industry started but was replaced when yellow sweet corns became popular. I suspect that’s because Aunt Mary’s has such a short window of opportunity for harvest.
I don’t remember them growing corn in the garden. There was just the big field of it that grandad planted. I think his corn might have been Aunt Mary’s and we had it for a treat a couple of days each year and he took the rest to the mill for flour or ground it for the chickens. He had another very different corn, too. It had big fat multicolored, very cone shaped ears but I don’t remember much about it or what he did with it. I think he just grew a little bit once in a while for fun. I grew it for a long time after he died but in my little patches if finally sort of withered away. I know he certainly wouldn’t have let it cross to his white field corn, he had a fit when neighbors across the road planted yellow and we had to inspect every seed ear to make sure there was no yellow in it.
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How could you tell the flour corn ears were ready to be enjoyed as sweet corn? Were there any telltale signs to watch for?
I’m curious because of course I want to try this myself now.
I’m planning to grow a popcorn landrace. I think I read somewhere (likely on this forum) that popcorn can double as a good grain corn. If it would do triple duty by working as a sweet corn when harvested at just the right stage, that would be really neat! 
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The same tells as sweetcorn usually, but like mark mentioned it usually only lasts a couple days for flourcorn. I’ll go out everyday when I notice the silks start to dry out, and press the kernel with my fingernail to see if it’s in the milk stage.
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