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Corn is my favorite plant to grow. It has beautiful luxuriantly green foliage, can grow to epic heights, and would look right at home in a tropical garden. It is also very diverse. There are varieties that can reach 15+ feet tall and others that top out at 3 or 4 feet. The cobs are works of art. They come in a huge range of colors, shapes and textures. Corn is also one of the most productive calorie crops on the planet, due in part to its highly efficient C4 photosynthesis.
The domestication of maize began in Mexico around 10,000 years ago, with the gradual improvement of its wild ancestor teosinte. Over the millennia, humans selected a huge amount of phenotypic diversity into the crop, and eventually it spread throughout most of North and South America. Just a few decades after the arrival of Europeans in the Americas, maize was being cultivated in Spain and soon spread throughout the Mediterranean region. Today it is grown all over the world, with the United States having the highest total production.
Growing Grain Corn
Maize is a warm season annual, and can be direct seeded after the last significant frost in the spring. I find that I can usually plant my seed a little early and, ideally, the last frost will occur just before the seedlings emerge. Seedlings will be able to tolerate a little frost damage, though, and grow back just fine. Your ideal planting time will depend on the length of your growing season, and the days to maturity of the variety your are planting. In California I have a 250 frost free days, so I can plant whenever I have time. If you live in a shorter season climate you may have to plant promtly at the earliest opportunity.
I typically grow small dense plots so I direct sow seeds around 3-6" apart and then thin to 12". My rows are usually 24" apart. Occasionally, I borrow a field to plant a larger crop, and then I stretch the spacing out to about 18x36". Some farmers sow maize in flats to transplant into the field, but I prefer to direct seed, since I think the plants end up with a better root system. It is also common for farmers to direct seed and also sow some flats to fill in any gaps in the rows later.
It can be tempting to thin as soon as seedlings emerge, but I always wait until they are 6" tall before thinning to the final spacing. Some seedlings put more growth into their root system before sending a lot of energy into their shoots, so they may appear to be less vigorous than their neighbors. I think there may be some benefit to this strategy since seedlings with a more developed root system may be more drought tolerant, and might also be more resistant to being pulled out by bird when young. However these seedlings will quickly catch up to the ones that grow their shoots first, and perhaps even surpass them by the time the corn is around 6" tall.
I live in a dry summer climate, so I have to irrgate my maize throughout the growing season. I lay down drip tape along my rows before I plant my seeds. Initially, I irrigate frequently until the seeds germinate -- every day if the weather is hot -- but after the seedlings emerge and start to get established, I quickly start to taper off my watering so that I'm irrigating longer but less frequently.
I have had a lot of problems with birds and other critters eating corn seeds either before or right after they sprout, so I usually cover the rows with hardware cloth cages or fabric row covers. After the plants are a few inches tall, I can remove the covers.
Maize usually only needs one weeding, and then it will grow enough that it can suppress weeds on its own. I usually hand pull the weeds closest to the corn plants, and use a hoe to kill the weeds growing in between the rows. Sometimes I also use the hoe to hill up soil around the base of the corn plants. This can help prevent more weeds from growing there, and may also help prevent lodging, but I'll admit I don't always do it. Usually I will cull lodged plants to remove them from the population.
In California we have a Mediterranean climate, and get no rain during the warm season. So I generally have to irrigate my corn throughout its growing season. The exception to this is if I plant a very short season variety, right around the last frost in spring (which is usually at the end of February), when the soil still holds plenty of moisture from the winter rainy season, and can support the plants until their crop is set. I use drip tape to irrigate, and usually water for about 2 hours twice a week at .4 gallons per foot per hour. I prefer to use manual timers when I am able to check on the plot at least a couple times a week. This way I can easily adjust the frequency based on the weather and the needs of the plants. My typical pattern is to water regularly until the seedlings are esablished, and then taper off in frequency to enourage the roots to grow more deeply in search of residual moisture. Once the plants begin flowering, I will usually be a little more careful to ensure that the crop gets adequate irrigation, since drought conditions during this period can severely affect yield. After the silks have dried and all the ears have been pollinated, I stop irrigating to help them dry down faster.
It is best to wait until the husks have turned completely brown before harvesting an ear. I am often tempted to pick the earlier, but I usually regret that. Sometimes the husks can be partially brown, and I think the ear is ripe, but when I harvest I find the the kernels are still soft and unripe. They will still continue to dry down after harvest, and the seeds will usually still be viable, but the endosperm will be less developed, so they will be lower quality as seed and as grain.
Sometimes when I am selecting for earliness, I harvest each ear as it ripens and use a felt tip marker to write a number on the husks denoting the order in which they ripened. After harvest, I husk the cobs and either hang them or place them on a drying rack until they are completely dry. Once they are all dry I go throught the whole bunch and pick out the best cobs to save seeds from. (See Inbreeding Depression below.)
Types of Maize
-Dent: Dent corn has a roughly equal ratio of flinty and floury endosperm. These hard and soft starch components are arranged so that the hard is all around the edge of the kernel, and the soft makes a column up the middle until it touches the flat top. As the kernel dries after harvest, the soft starch shrinks much more the the hard, and creates the characteristic dent. Ther are also many corn varieties that have a ratio of flint to flour similar to dent corn, but the soft starch in the middle does not run all the way to the top of the kernel; these are refered to as flint/flour types. I believe that the purpose of the dent (which must be selected for in the breeding process) was to enable farmers to quickly assess starch composition of the corn kernels they are working with.
Dent corn is the most commonly grown type in the US for cornmeal, hominy, masa, corn flour, corn starch, corn oil, animal feed, silage, and industrial uses. Modern Corn Belt Dent varieties got their start in the 1800s resulting from crosses between Northern Flint corn and southern Gourdseed Corn. This is the group of corns most commonly grown in the US as a commodity crop for industrial processing and animal feed. They are almost entirely F1 hybrids, and probably all the GMO corns are part of this group. The Corn Belt Dents make up the great majority of corn grown in the US. Some of the heirlooms from this group include, Reid's Yellow Dent, Lancaster, Nothstine, Wapsie Valley, and Blue Clarage. Southern Dent Corn is an older group that has been grown by the native people of the of the southeastern US for centuries, and are probably descended from the dent corns of southern Mexico. Heirlooms from this group include, Hickory King, Tennessee Red Cob, Boone County White, and Cherokee Gourdseed.
-Flint: Flint corns have mostly hard starch in the endosperm, and are very glassy looking and resistant to moisture.
Direct sow 3-6” apart. Thin to 12”. Rows 24” apart. Sow any time during warm season depending on length of growing season. I have 250 frost free days. Keep seeds moist until germination. Wait until plants are about 6” tall to thin. Some may grow root systems first. Taper off watering after thinning, to end up at deep infrequent waterings to encourage deep roots.
Usually needs only one weeding and then it suppresses weeds. Maybe hill up around stalks. Cull lodged plants if possible to remove from genepool. I water for 2 hours twice a week .4 gallons per foot per hour. I use manual timers, so I water when the plants look drought stressed. I water a little extra when the plants are flowering since I usually grow small plots and want to ensure a good harvest. When I occasionally grow a larger plot, don’t worry about watering extra during flowering because I want to cull those that need it. Once most of the silks have dried, i stop watering to help ears dry down faster.
Once the husks on an ear have turned mostly brown it is ripe enough to harvest. When I am selecting for earliness I often harvest each ear as it ripens so that I can give it a number according to when it ripened. As soon as it is harvested, I husk it and put it in a well ventilated place to finish drying.
Types of Maize:
Flint: Mostly hard flinty endosperm, good for polenta, dries down more easily in high humidity, more reliable in humid climates or short seasons
Flour: Mostly floury endosperm, grinds easily into fine flour, good for parching, needs more care to prevent mold
Dent: Nearly equal mix of flint and flour endosperm, good for grinding into corn meal or flour, good for hominy. The most commonly grown type.
Maize has a special adaptation to help deal with heat and drought stress. Most plants have only C3 chloroplasts, which use the sun’s energy to process carbon dioxide into a 3 carbon molecule, which will be processed into carbohydrates that feed the plant. O2 is a waste product of this process. Under ideal conditions of temps and adequate moisture, O2 is released through the stomata of the leaves, but under drought or high heat conditions, the stomata must close to conserve water, and the O2 is trapped inside the leaf. Once the ratio of carbon:oxygen starts to tip towards the oxygen A buildup of O2 can be toxic to the plant, so it uses a process called photorespiration to bind the oxygen until it can be released. A problem arises because the plant stops fixing carbon while it is binding oxygen. To remedy this situation, maize also has C4 chloroplasts which fix carbon into a 4 carbon molecule, thereby increasing the carbon levels in comparison to oxygen.
Inbreeding Depression: Maize is susceptible to inbreeding depression when it is grown in a population that is too small. Conventional wisdom says that you must grow a population of at least 200 plants if you want to save seeds without the risk of inbreeding depression, but there are a few caveats to that. This is assuming that you are growing a stable variety which is already somewhat inbred to begin with. If you are growing a more diverse variety, such as Painted Mountain, Magic Manna, Astronomy Domine, you can probably get away with a smaller plot. I believe one of the reasons for maize needing a larger plot is that its pollen is distributed by wind, but if the male flowers open on a morning when there is no wind, most of the pollen drops straight down and gets received by the silks of the same plant, resulting in self pollination -- which is the worst scenario for and outbreeding plant. My strategy for overcoming this problem, in small plots of corn, is to do some hand pollination. I usually do this some time in the late morning, when the anthers are dehiscing and releasing pollen. I just strip off some of the anthers with my fingers and sprinkle the pollen over the silks of plants on the other side of the corn patch. Sometimes I use a bowl to hold the pollen while I carry it around. This technique is also helpful when crossing corn varieties to create new breeding populations. I usually do it every other day over about 10 days, although I don’t worry too much about the exact timing.
The other method I use for avoiding inbreeding depression, in small maize populations, is to set aside some seeds from my original seed lot to plant along with subsequent generations. In this way, every time I plant, I am putting in seeds from 2 to 4 different generations of the same population. This helps to retain genetic diversity, though it may slow down any selection you are doing. Of course, if you are able to plant 200 or more plants, these methods will not be necessary.
Selecting Seed Cobs: Once the silks have turned brown, that ear will start developing its seeds. It is best to wait until the husks have turned completely brown before harvesting that ear from the plant. In reality, there is a wide range in the time it takes for the kernels to be ripe enough to harvest. With some varieties, you can harvest with husks still mostly green, and the kernels will be hard and fully ripe; with other varieties, you can harvest when the husks are 90% brown, and the kernels will still be in the milk stage -- and it is very disappointing when you find that.
Kernels harvested in the milk stage will still have a viable embryo, but the endosperm will be less developed than in a kernel that is allowed to dry down completely on the plant. Since the endosperm is the food for the germinating embryo, seeds with a less developed endosperm will produce weaker seedlings. These underdeveloped seeds may still be worth planting though, if they have other desirable traits, since the root system will eventually get established, start feeding the plant itself, and if you don’t let it get smothered by its neighbors grown from fully developed seeds, the plant should be able to catch up. The problem arises in the weak seedling stage, when the plant is more vulnerable to predation, and competition.
I have a hard time stopping myself from harvesting each cob as soon as I think it’s ripe enough, and I often regret it, so just be warned that it is always better to wait a little longer. Though I will say that in my breeding populations there is some benefit in harvesting on the early side, which is that I’m automatically selecting for plants that ripen up quickly. In fact, in the early stages of a breeding project, I prefer to harvest each cob as it ripens, so that I can select strongly for those early ripening genetics.
You also need to decide on your selection characteristics. This will certainly differ depending on whether you are starting with a diverse breeding population or an open pollinated heirloom. Firstly, you will probably want to select for yield. This can be accomplished by selecting the largest cobs and those from plants that produce multiple good ears. Yield has to be balanced against earliness, though, since the highest yielding maize varieties tend to be large plants requiring a long season to reach full maturity. I try to achieve this balance by selecting the earliest and best yielding cobs for seed, and culling the latest 10% even if they produced a good yield.
Next you will need to select for your desired grain and ear characteristics. This will usually mean assessing the ratio and arrangement of flint and flour endosperm and the size of the kernel, and observing the number of kernel rows, and the length and thickness of the cob. Kernel characteristics affect how the grain is used for food, so are one of the most important selection criteria. The ratio of flint to flour in the endosperm can be anything from very pure flour, with only a shell of flint around the outside of the kernel, to pure flint with only the tiniest bit of flour in the middle, and everything in between. Whatever kernel characteristic you choose it is probably best to have that trait relatively uniform, whatever other traits you select for in the rest of the plant, so that the eating characteristics are predictable. Of course, if you are growing corn for chicken feed or ornamental use, the flint/flour ratio may not be essential.
Ear characteristics include cob length and thickness, number of kernel rows, and husk qualities. Cob thickness has a marked effect on speed of drying, so if you live in a humid climate you will want thinner cobs -- which usually have 8 rows of kernels. I am generally not too picky about cob traits, and I actually try to keep plenty of diversity in my maize populations, so I welcome all different cob dimensions and row numbers, as long as they don’t reduce yield. Different maize varieties can have husks that are paper-thin or tough and leathery. I haven’t put a lot of thought into selecting for husk qualities except that they remain well attached to the cob after husking. Tight, tough husks can also help to prevent pest damage. Some varieties have more layers of husks, which may be good if you are harvesting them for tamale wrappers.
Finally, you will select for plant characteristics, such as plant height, ear placement and number, lodging resistance, and climate tolerance. Plant height is mostly a matter of preference. Really tall plants are pretty impressive, though they sometimes can be more prone to lodging. There is a lot to like about a shorter corn that makes nice large ears. Ears can also be formed high or low on the plant, which both have advantages and disadvantages. Really high ears can be tough to harvest without using a ladder or knocking the whole plant over, but they can help to deter pests. Ears that are formed between 4-6’ on the plant seem to be the easiest to harvest. Some really short corn varieties have ears below 3’ and require a lot of bending over to harvest. You also need to decide whether you want your plants to have tillers or not. Most modern corns have been selected for a single stalk with no tillers, but many heirloom varieties do have them. I’m not sure if tillers have much benefit in a corn population, although they can sometimes produce tassels and later release of pollen which may help to pollinate later silks. They may be more useful if you are planting your maize on a wide spacing, but not much if you are planting densely. Although I do tend to plant densely, I don’t select too hard against tillers, just because I have an affection for atavistic traits.
Lodging usually happens during windy days or when the soil is too loose. Sometimes the roots will pull right up out of the soil, and other times the stalk will bend anywhere from just above the base to 6’ up. Often lodged or broken plants will still produce good cobs, but it is usually worthwhile to cull those cobs from your seed lot. Maize can adapt to a wide range of climates which vary in rainfall patterns, humidity, disease resistance, temperature range, and length of season. For the most part, selection for adaptation to your climate happens automatically when you select for yield, but sometimes it helps to think about which specific traits might help your maize adjust to your climate. I live in a very hot and dry climate with zero rainfall in summer, so drought tolerance is a very important quality for me. I am not sure which genetic traits confer heat tolerance, but I have read that some drought tolerance comes from having a large and vigorous root system. I don’t ever dig up the roots of maize plants to inspect the root system, but I do try to look for plants which put energy into their roots first and shoot second. I do this by looking for seedlings that seem to start off slowly, but catch up quickly. Mostly though, I select for drought tolerance just by irrigating a little less than I would if I was growing only for food and not saving seeds, and then selecting for yield as usual.
Drying Down: Once the cobs are harvested, I immediately husk them so that they will dry more quickly. I usually leave the husks peeled back, but still attached and tied up with a twist-tie, so I can write notes on them with a sharpie, or hang them as fall decorations. It is not necessary to leave the husks on though. After husking, I set the cobs out on an indoor rack with good airflow, or hung from a wire on my covered porch, to dry down completely. If you live in a humid climate, you may need extra measures to prevent mold, like placing the cobs in front of a fan. Also more flinty varieties dry down much easier than floury ones, so if you live in a humid climate, you may want to grow flint corn. I live in a very dry climate and my maize crop usually dries down very easily. One time I stuck some undried flour corn in a box just overnight, to clear up some space, and when I opened it in the morning, they were already covered in mold. Airflow is crucial, even in dry climates.
I usually keep the kernels on the cob until they are fully dry, then I shell them and store them in jars or ziplock bags until I use them. Some people, in more humid climates, leave them on the cob just until the kernels are dry enough to wiggle, then shell them and leave them to finish drying in front of a fan or in a dehydrator at the lowest temperature.
Utilizing Grain Corn:
Cornmeal: I make cornmeal from a dent (or flint/flour) corn ground with my hand crank Corona grain mill. You just have to adjust the grinding plates to the right spacing with a little experimentation.
Nixtamalization: Nixtamal is made by boiling the whole kernels in an alkaline solution of calcium hydroxide (cal or pickling lime) and water, until the skins slip off. Then they are soaked or boiled until soft. These nixtamalized kernels can be eaten whole, as hominy, or ground into masa to make tortillas or tamales.
Corn Flour: Some corns have very pure floury endosperm, and can be ground into a fine flour using a hand crank grinder. Dent of flint/flour varieties can also be ground into flour using an electric grain mill. I use my Wonder Mill to grind flour from dent or flour corn varieties.
Polenta/Grits: These are usually made from coarse ground flint corn, or dent corn with the floury endosperm sifted out. Some very pure flints don’t need to be sifted, but even many flint varieties have a fair amount of flour in them. I highly recommend The Resilient Gardener by Carol Deppe which has much discussion of how to use different types of grain corn as a staple crop at home.
My Breeding Projects
Flour Corn with Colored Pericarp: I started this breeding project with Magic Manna, which is a very pure flour corn bred by Carol Deppe from selections of Painted Mountain flour corn. This is a really nice flour corn suitable for fairly short season climates. It is fairly short (4-6’) and matures in around 85 days (though probably a little earlier in my hot summer weather). Since I have such a long growing season, I don’t necessarily need such an early corn. Early varieties also have the drawback of being somewhat less productive. I really wanted a flour corn that matures in around 95-100 days. So, I grew out a plot of Magic Manna and selected the largest (most productive) cobs, and the following year crossed them with several other flour varieties such as, Walpole Island White, Hopi Pink, Oxbow White, Unity Flour, Tohono O’odham 60 Day, and a long day/northern adapted strain of Kculli/Maiz Morado. Most of these are somewhat longer season than Magic Manna, although the Tohono O’odham 60 is a bit earlier.
Magic Manna has diverse pericarp colors, ranging from clear through deep red to brown, but it has only white endosperm and colorless aleurone. I plan to keep this color scheme, but possibly add in some other pericarp colors. Most of the varieties I crossed in are completely white, but Hopi Pink has pink pericarp, and Kculli/Maiz Morado has a deep purple, almost black pericarp. The latter is really beautiful, but the pericarp color is completely opaque and covers up any other colors that might be beneath it. So, on any of these super dark pericarp kernels, I use a file to scrape through the outer layer and and see any aleurone or endosperm colors, and only plant kernels that are completely white underneath. Unity Flour is an intentionally diverse landrace selected by Joseph Lofthouse out of crosses between many North and South American grain corns. This also contains some colored endosperm and aleurone and, even though I didn’t plant any kernels that showed these traits, there were probably some recessive gene hiding there which will show up in later generations. Unity is also not quite as pure a flour corn as Magic Manna, but it probably contains some desirable traits like drought, heat and disease resistance. I will rogue out any undesirable traits as the project continues, but even in its current state it is turning out to be a really good flour corn.
Orange Flint Corn: