Growing Corn, Part 1

I love corn.  It's simultaneously easy and tricky to grow, suffers few pests and diseases compared to some other garden plants, and is very productive.

When I say I love corn, I'm talking about dent corn, primarily.  I have grown sweet corn, and definitely like eating it right off the cob--raw or cooked somehow.  But sweet corn has issues when it comes to home gardening.

Preserving sweet corn is a hassle.  It can be cut off the cob and frozen, but what a mess.  It can be dried (on the plant or cut off and put in a dehydrator), but why bother?  At that point you basically have dent corn.  Or sweet corn can be frozen on the cob.  Some method of preservation would be needed with any decent amount of production because non-super sweet  (mostly open-pollinated heritage) varieties have to be picked then eaten or preserved within a fairly narrow time window. Some method of preservation would be needed even with super sweets, which are more stable once picked (thus enabling you to buy them in the store days after picking).  Staggering planting is one option, but then you run into pollination issues.  You will have to more intensively manage things if you try planting six corn seeds per week in the spring.

Dent corn is more limited for fresh eating, but it is possible (and although I keep mentioning dent, these comments would also apply to varying degrees to flour, flint, and popcorn).  I have eaten Blue Clarage dent corn in the milk stage and thought it was fine as a sweet corn (though I might not be a corn connoisseur, so I'm not guaranteeing others would like it).  A stand of dent could conceivably provide for summer corn on the cob as well as cornbread and more for months afterward.  Of course, making cornbread requires shelling (discussed  previously) and then grinding, which could be considered hassles in their own way.  Popcorn eaten as popcorn is probably the easiest way to use a non-sweet variety, with parching a close second (something I have no experience with or [for now] interest in, following an inauspicious introduction to Corn Nuts when I was in high school).

There are some potential pitfalls with home-scale corn production.  The first is the need for nitrogen.  Corn is notoriously greedy when it comes to nitrogen, and at varying times of its growth cycle, it needs a lot of it.  It will deplete whatever's there and look for more.  You can provide a gentle boost of nitrogen to the soil around the developing plants by spreading compost, fresh grass clippings, or side-dressing with a fertilizer: either 10-10-10, lawn fertilizer, blood meal, or something similar.  As the figure shows, about 75% of the plant's total nitrogen uptake happens by or around the time of tassling (VT) and silking (R1).  What this means is you need to be giving it nitrogen fertilizer as it's growing and putting on leaves before you see tassels--if you wait until then, you have potentially compromised your harvest.

After R1, however, a lot of the plant's total phosphorous needs are still to be met--that's something worth keeping in mind.  University extension services provide more information than this on their sites, particularly those located in corn country.

The growth stages, btw, are pretty simple.  Anything with a V refers to the vegetative stage and happens before the silks appear.  Once the silks emerge, the plant is in the reproductive phase, identified by Rx, where x=1, 2,...6.

Sweet corn is picked in the milk stage, or R3.  This typically happens about 18-22 days after silking, according to this site (the picture to the right is actually clickable at the site, allowing you to get information about each stage).  Other sites will tell you to partially shuck an ear, exposing the tip, and pierce a kernel with your fingernail--if the fluid is milky in appearance, it's ready to pick.  However, if you don't keep an eye on it, it will rapidly progress into R4, the dough stage, where it will still work as sweet corn but will be rapidly trending in a direction you won't like for fresh eating.

When I was in school I worked for several summers at a Pioneer Hi-Bred research nursery, where we worked with new corn varieties.  Mostly we pollinated them, inbreeding them for several generations to see if bad traits emerged. We also challenged them with insect and disease pests (maybe challenge isn't the right word, because they hadn't necessarily been provided any defense against the pests--but my understanding of what was going on at the time was limited).  At any rate, the company always planted some ranges of sweet corn for employee use; one year we were given some at the appropriate time--which was fine--and I tried to pick and eat a couple of ears later in the summer after it had reached R4 or even later.  It was still edible, but not that good.  As noted above, diligent monitoring is important to get it at the right time.  Harvesting dent or flint is easier: just let it dry down on the plant, then pick.

Something else about timing a sweet corn harvest:  Going by the days listed on the seed packet is not necessarily the best approach (although using the 18-22 days mentioned above for R3 after silk emergence will probably work okay in most cases).  The advertised days to harvest (e.g.,  78 days for Honey 'n' Pearl, the variety planted by Pioneer for us pollinators during that summer mentioned above) are only approximations. They probably apply to corn belt conditions.  Corn growth can be more precisely tracked with degree days.  This link and (better) this link (both from the University of Kentucky) provide information on degree days (see slides 16 and following in Chad Lee's presentation).  The calculations are simple enough, but you won't want to do them manually for each day after planting.  Fortunately, online calculators are available.  Here is one:

Pioneer Hi-Bred Calculator

Georgia has them for the state, as do others (for Georgia, pick a station and then go to the degree day calculator: base temperature 50, disregard temps above 86).  Pioneer's is nationwide.  To use it, you want growing degree units, GDUs, not crop heat units, CHUs, if you want to use the general guidelines in the UKY presentation.

Chad Lee's presentation doesn't mention R3, the most relevant stage for sweet corn, because it's not that relevant for corn harvested as grain.  If I had planted sweet corn on April 1 this summer (which I didn't), I would've experienced about 1950 GDD so far. The figures he presented at the top of Slide 18 refer to maturity, or R6.  Using straight line extrapolation for the figures he presented for a 2700 GDD hybrid, R3 would be expected to occur at 1920 GDDs.  That suggests now might be a good time to harvest, but it would also be about 93 days after planting... sticking to about three weeks after silking is probably a better approach.  At R1 you know what stage the kernels are at, but the time from planting to silking is going to be somewhat variable.

Last summer I planted Blue Clarage, which Southern Exposure Seed Exchange (my source) lists as a 100-day variety. Chad Lee's presentation suggests about 2400 GDDs are needed to get it to maturity; I harvested it at 2677 GDDs.  It was obviously drying down at about 2400 GDDs and I probably could've harvested it then.  The picture at right shows how the little stand looked at the time of harvest (along with the failed deer abatement method I mentioned a couple of weeks ago).  As noted previously, about the only thing I got out of the garden last year was corn.


There are some other things worth mentioning about corn, but this has gone way long so I'll take that up another time.