My apologies for the long post. What can I say- Corn is complicated.
Corn is the un-vegetable. It’s really a cereal crop. In my opinion it’s one of the hardest crops to grow, and not necessarily worth the effort and space that it requires, but I know that some people, like my husband, are huge corn fans and feel that no summer garden should be without it. For that reason I grow corn every year and I find lots to like about growing it: growing such tall plants feels like an accomplishment, Brian grining as he eats ear after ear right off the plant, people lavishing praise upon me when I give them fresh corn, and oh yeah, I like eating smut… more about that later.
Another cool thing about growing corn is that corn genetics are really complicated and this bears out in interesting ways when you plant different corn cultivars. You can see how much plant breeders have changed corn's genetics when you plant an heirloom sweet corn next to a modern hybrid; it’s like watching the green revolution in action. Last year I planted two corn cultivars ‘Silver Queen’, an old Open Pollinated Cultivar and ‘Bodaceous’ a modern hybrid with the sugary enhanced gene. The differences were remarkable.
Silver queen grew two feet taller than Bodacious, and the plants grew multiple side shoots, called tillers, whereas Bodacious had no tillers. Bodacious yielded earlier and consistently yielded two identical ears of corn per plant, and all the ears were ready at the same time. Silver Queen yielded one perfect ear of corn per stalk, ready first, then a second half ear a few days later, then another one or two of half ears on the tillers a couple of weeks later (many of the tiller ears developed smut!). Overall Silver Queen made a little more corn, but the plants were bigger, more raggedy looking, and the half ears weren’t all that high quality compared to the Bodacious ears.
Flavor-wise, when Silver Queen and Bodacious were eaten right off the plant, they were similar, silver queen’s kernels might have been a little thinner skinned, and the meat of the kernel (endosperm) a little firmer, but overall they were equally sweet (sweetness IMO is the single dimension of corn flavor… which may be why I’m not crazy about it). The difference between the two cultivars was much more noticeable when I took corn home and stored it a day or two before eating it. Even after a few hours off of the plant the silver queen became starchy and less sweet, while the bodacious maintained its sweetness for a few days.
Longer shelf life is a hallmark of the sugary enhanced (se) gene that Bodacious carries. There are a number of different hybrid sweet corn types with a number of different named genes that confer a number of different traits. Some of these genes are incompatible with one-another for pollination, so plants of different genotypes have to be isolated. This article http://www.rec.udel.edu/Update08/Volume16,Issue7.pdf from the University of Delaware breaks down the details of sweet corn genetics, and isolation requirements better than I have the ability or desire to do.
For the average gardener in the EC garden stick with open pollinated or sugary enhanced sweet corn and make sure that they are isolated by at least 350’ from popcorn or field corn to avoid cross pollination that will make the kernels starchy. The fancier sweet corn varieties are only available from seed catalogs; most people don’t grow them so you don’t have to worry about accidentally picking up the wrong type of seed at the nursery or the wrong type of pollen coming over from somebody else’s plot.
Ok, friggin enough nerd-talk about corn genetics. Once you get past seed selection there are a number of issues I’ve run into and I’ve seen others run into growing corn. First of all, Corn is a heavy feeder. Beds need to be amended with something high in nitrogen, like manure, not so much that the plants will burn, but the high carbon low nitrogen rice hully ‘manure’ available in the garden just won’t do. The stinky green manure can work, but it will burn the plants if you use too much. Last year I used a lot of boxed organic vegetable fertilizer. It was expensive, but it worked great. This year I have a lot of high nitrogen compost, so I’m using that.
Because corn is wind pollinated it needs to be planted in a patch of at least nine plants in a circle or square, not a row so that they can pollinate each other. Keep this in mind as you are laying out your planting area. Also keep in mind that corn uses a lot of water, so hand watering is not recommended. For irrigation I’d recommend laying out T-tape or drip line in the planting area and direct sowing along the line. It is not necessary to plant corn in raised beds. In the past I’ve just turned the soil in rows and raked out narrow, shovel width, seed beds. I make my rows 36” apart, a little wider than recommended on the seed packet, for ease of harvesting (sometimes the plants get covered in aphids at the end of the season and it sucks to have to get too close when you’re harvesting). I plant seeds 4 inches apart and thin to the strongest plants 8-12 inches apart.
The minimum germination temperature for corn is 50 F and optimum temperature is 60-95 F, that means that in Davis, the window for planting corn starts at the beginning of March and goes until early June. I planted corn on Memorial Day a couple of years ago and had a great harvest in Mid September. You can plant a few plants every couple of weeks during this period to have a continuous harvest of corn throughout the late summer and fall. As with all large seeds, soak overnight before planting to aid germination.
Pests and diseases abound with corn. The first problem you will likely encounter is birds eating your seedlings. Seedlings should be netted until they are about 10” tall to prevent this. Corn grows so fast that you can almost see it getting bigger in the June heat. It’s not usually bothered by pests and diseases during this time unless it is stressed from too much or too little water or fertility.
Most of the pest and disease damage starts to occur once the ears start to form. Corn ear worms will eat the kernels near the tip of the ear, you can either poison them with Bt when the corn silks show up, or just cut the damaged part of the ear off at harvest like I do. Aphids are a problem towards the end of the season. They tend to attack the open pollinated corn after I’ve harvested the first ears. They’re less of a problem with the hybrid corn since the harvest comes all at once. I use a strong jet of water from the hose to knock down aphids, if I bother with them at all.
The most annoying pest is the rodents, rats and squirrels, which come at night, peel away the husks, and eat all the kernels off of the corn. These guys are deterred somewhat by fences, but I’ve had the best success controlling rodents in the garden by cutting down weeds and brush in surrounding abandoned plots and on domes land (with permission), thereby reducing rodent habitat. I’ve also heard people suggest planting corn early so that you harvest before the rodents have had their babies for the season and the rodent populations are low. I’ve gotten lots of good late harvests though, so this seems unnecessary at least in my area of the garden.
How do you know when to harvest corn? The first sign is when the silk sticking out of the end of the ear turns brown. Next, feel the ear of corn through the husk, it should fell nice and full. If it feels full, you can pull back the husk and pop a kernel with your finger nail, the juice that comes out should look half way between water and milk. If it is watery the ear isn’t ready. If it is very opaque the corn is starchy and past it’s prime.
When you’ve picked your corn ears and shucked them look out for any enlarged gray kernels. These kernels have been infected with a fungal disease called smut. Don’t worry, if you have these you are very lucky indeed, because smut is edible and delicious. In fact, I consider it one of the redeeming qualities of sweet corn. Cut the kernels off of a smutty ear of corn (if they’re black and smell of ammonia, they’re too old, throw them out; plump and gray is what you’re looking for) and sauté them with a little garlic, then use it to fill a quesadilla. The flavor is earthy and complex in addition to sweet… Wonderful!
Open Pollinated: Silver Queen, Golden Bantam
Hybrids: I haven't tested a lot of these out. Look for sugary enhanced cultivars because they're compatible with open pollinated types, they'll have the (se) symbol on the packet somewhere. Also look at the number of days to maturity. In general, the later season cultivars with the greater number of days to maturity are higher quality. Plant early season corn only if you want an earlier harvest. This year I'm trying out a number of hybrids including: Delectable, Spring Treat, and Argent. Bodacious will also make a repeat appearence.
2 days ago