Green Man Publishing

Corn

Zea mays

Introduction: This warm weather annual differs from all other common garden vegetables in being the only a member of the grass family (Poaceae). It is thought to have originated somewhere in Central America, though it is no longer found anywhere as a wild plant (it may be descended from the closely related Teosinte, which is still found in the wild in Mexico). It also differs from most other vegetable crops in being a highly productive and easily used staple food crop. Native people have cultivated corn for over 5000 years and it has its own distinct personality, which made it not only a staple food, but also an integral part of their culture.

Corn was introduced into Europe in the sixteenth century and spread from there to all suitable climates around the world. There are several different types of corn (see Varieties), but they are all grown in much the same way, only their uses differ.

Nutritional content: Sweet corn is rich in carbohydrate, as well as soluble fiber, folate, niacin, thiamin and phosphorus. It also contains useful phytochemicals. Yellow varieties also contain vitamin A.

Field corn is rich in protein, carbohydrates, potassium, calcium and the amino acids leucine and methionine (the latter is lacking in beans, which is why they go together so well).

Niacin: When corn was introduced to the rest of the world in the sixteenth and seventeenth centuries a little snippet of important information was left behind in its homeland. The niacin in corn is not very available and requires special processing before humans are able to make use of it. As corn became a staple food in many poor areas a problem developed, as some people started to show symptoms of niacin deficiency. This results in an unpleasant deficiency disease called pellagra.

In its native land corn is soaked in an alkaline solution of water and calcium hydroxide (slaked lime) or wood ashes. This process is known as nixtamalization and has several important effects. The most important is that it makes the niacin in the corn more available. It also softens the cellulose in the seed, making it easier to grind and making it possible to make it into dough for making tortillas.

Crop value: Sweet corn is one of the ultimate treats of the summer garden (it makes my mouth water thinking about it), but it isn’t really a good crop for small gardens. You need quite few plants to ensure good pollination and they aren’t very productive for the space they require.

From a nutritional and self sufficiency viewpoint field corn is much more important than sweet corn. It is one of the easiest and most productive of all cereal crops to grow and process and it can be used in a variety of ways for making cornbread, tortillas, polenta and more.

Anyone seeking food self sufficiency in a warm climate will probably end up growing a lot of corn (emulating many peasants around the world).

If you want to use corn as a staple food it needs to be processed to make its niacin available. Fortunately this is pretty easy to do (see Nixtamalization below).


Ease of growing: Corn is a fairly easy and reliable crop to grow if you give it moist, fertile soil and warm weather.


Climate: Corn is a subtropical plant and uses C4 photosynthesis, which enables it to grow more efficiently in high heat and light levels. For best growth it needs warm weather and as much sunlight as it can get. If it doesn’t get full sun all day it will grow more slowly and won’t be as productive.

Soil

pH 5.5 (6.0 – 6.8)

Corn grows well in a variety of soils, but it is a hungry plant and needs a lot of nutrients for maximum production. The ideal soil is rich, moisture retentive and well-drained. Field corn isn’t quite as demanding as sweet corn, but the better the soil the better the crop.

Soil preparation: This vigorous and fast growing crop needs generous amounts of nitrogen, phosphorus and potassium, as well as all of the other plant nutrients.

Incorporate 2˝ of compost or aged manure into the top 8˝ of soil, along with colloidal phosphate (for phosphorus) and wood ashes (for potassium). Add kelp to supply the necessary trace elements. Alternatively you could use an organic fertilizer mix to supply these nutrients,

Corn is sometimes planted into a bed 2 weeks after a nitrogen fixing winter cover crop (such as fava beans) is incorporated.

Legend has it that Native Americans put a fish in each hill of corn, to supply the necessary nutrients. This isn’t true though, when soil fertility started to decline they would just move their gardens to new soil (one of the advantages of not “owning” land).

Planning

Where: Sweet corn can be grown in an intensive bed, but it should be in a large block for best pollination. It is a tall growing plant, so must be planted where it won’t shade other plants. If you are growing SH2 or SY types they need to be isolated from other types, either by time (10 days) or distance (at least 25 ft).

Field corn should probably be grown in its own separate patch, as you will need to plant quite a large area if you want to produce a significant quantity of food. You might want to try growing it in a polyculture with squash and beans (see Three Sisters for more on this).

Crop rotation: Don’t plant corn in the same soil for at least 3 years. In a rotation it commonly follows a nitrogen-fixing legume.

When: Don’t plant corn until at least 2 weeks after the last frost date, when the soil has warmed up to a minimum of 60˚F (75˚F for the more temperamental supersweet varieties). Native Americans traditionally waited until the plum trees bloomed, or the oak leaves were emerging before planting. In cold soil, the seed takes a long time to germinate and there is a much greater chance of loss to rot or some hungry creature.

Day length: Though it isn’t as critical as with some crops, corn is day length sensitive to a varying degree (some varieties more than others). If it is planted too late in the year it will often flower while the plants are quite small and there won’t be much of a harvest.

Succession sowing: In the home garden you don’t want a lot of corn ripening at once (unless you are going to freeze it). You can stagger the harvest, by succession sowing a block every 2 – 3 weeks. You could also plant several varieties with different maturation times.

About Corn  

Seed facts
Germ temp: 50 (60 – 75) – 95˚F
Germ time: 3 – 10 days
22 days / 50˚F
12 days / 59˚F
7 days / 68˚F
4 days / 77˚F * Optimum
4 days / 86˚F
3 days / 95˚F
Seed viability:
                    Sweet Corn 1 – 3 years
                     Field Corn 3 – 5 years
Germination percentage: 75%+
Weeks to grow transplant: 3 – 4  

Planning facts
Hardiness: Tender
Growing temp: 50 (60 – 75) 95˚F
Plants per person: 15
Plants per sq ft: 1 plant needs 1 – 2 sq ft
Days to harvest: 60 – 150 days  

Planting Transplants:
Start: 2 wks before last frost
Plant out: 2 wks after last frost
Direct sow: 2 wks after last frost  

Harvest facts
Harvest period: 2 – 3 weeks
Yield per plant: 2 – 4 ears
Yield per sq ft: 1 – 3 ears  

Planting

Transplants

Starting inside: Corn can be started indoors, but this is only worthwhile for very early corn, where the growing season is exceptionally short (or cool), or to avoid predators such as birds and mice.

It is best to start corn seed in cell packs, soil blocks or plug trays as it doesn’t really like disturbance. Sow 2 seeds in each cell or block and thin to the best one when they have all emerged. If germination is likely to be very good, you might just plant one seed per cell. The seedlings grow rapidly and will get root-bound if left in their containers for very long. Ideally they should be out of their pots and in the ground within 3 weeks.

Direct sowing: Corn is usually direct sown, because it grows fast, doesn’t like transplanting and it is less work. In spring when the soil is cool, it should be planted only 1˝ deep. Later in the year, when the soil is warm, it may be planted as deep as 4˝. The less vigorous seed of hybrid varieties is usually planted only ¾ – 1˝ deep (this should be consistent as they are sensitive to this). Plant twice as many seeds as you need and thin to the desired spacing when they are several inches high.

To get the plants off to a good start, you can soak the seeds overnight prior to planting (sweet corn is more temperamental than field corn and needs more moisture to germinate). For an even faster start you could pre-germinate them, but be careful not to break the brittle roots

In some areas mice or birds can be a major problem in spring, in which case you can use rows covers (these also keep the seedlings warmer).

Hill planting: Native Americans used to plant their corn in hills. These were quite literally small flattened mounds about 18˝ in diameter. They planted 6 – 8 seeds in each hill, at a depth of 2 – 4˝ and spaced evenly in a circle about 9˝ in diameter. The hills were spaced about 4 feet apart in the rows and there was about 4 feet between the rows.

Row planting: Corn is usually planted in rows, but to ensure good pollination (which means full ears) it is important that the rows be in blocks. These should consist of at least four rows each.

Spacing:

Rows: Put the plants 6 – 8˝ apart in the rows, with 24 – 36˝ between the rows.

Beds: Plant in offsets rows across the bed. The distance apart depends upon the soil:

18˝ (poor soil)

15˝ (average soil)

12˝ (excellent soil)

Poor emergence

This may be caused by several factors; cold or wet soil, poor seed, birds, mice, rotting of seed, soil compaction or crusting, insects, disease or too deep planting. Sweet corn is more vulnerable than other types because it contains less food in the form of starch (the sh2 and se types are particularly temperamental).

Care

Weeding: It is important to weed the plants carefully while they are young. After they reach 12˝ in height they can deal with almost any weed. The young plants can be hoed quite closely, as they don’t have shallow roots.

Water: Sweet corn is a thirsty plant and needs a constant supply of water for best growth. This is especially crucial during tasselling and subsequent ear maturation. A soaker hose or drip system is the best way to irrigate. Be careful when overhead watering as it can interfere with fertilization during the pollen shedding stage.

Generally field corn needs significantly less water than sweet corn, especially those varieties bred for growing in dry climates.

Fertilization: It is a good idea to give the young plants a boost of nitrogen (such as compost tea or liquid kelp) when the seedlings are about 12˝ tall and growing rapidly. Give them another boost when the silks appear.

Pollination: Corn is wind-pollinated and getting good pollination is a critical aspect of corn growing. If you don’t get good pollination, the ears may be only half filled and you won’t have a good crop. Overhead irrigation and wet weather can impede pollination

The male tassel on top of the plant gives off pollen for a couple of days before the female flowers (the silks) become receptive. When the silks are receptive, you can improve pollination by gently shaking the plants, so pollen comes cascading down from the tassels. This should be done on a still day of course.

In some cases the type of pollen a plant receives will determines its taste characteristics. This means you should ideally only have one kind of corn flowering at one time (unless you are prepared to hand pollinate).

Genetic purity is most important with the super sweet hybrids and they should probably be isolated from all other types of corn. It is not so important for field corn, unless you are saving the seed for planting (in which case you may want to hand pollinate).

It is helpful to note when half of your sweet corn plants are showing silks, because they will be ready to harvest from 18 – 22 days later. The exact time depends upon temperature and growing conditions.

Suckers: Corn plants often produce suckers, smaller stems, which if left alone may eventually flower and produce small ears. Some people believe theses drain energy from the plant and remove them as they appear. This isn’t really necessary though.

Problems

Pests: Many pests attack corn at various stages of growth. These include cutworms, corn rootworms, wireworms, aphids, flea beetles, corn earworm, corn borers, Japanese beetles, sap beetles, raccoons, squirrels and birds.

Corn Earworm: This is perhaps the most common corn pest. It burrows down into the ear, eating the seeds and making quite a mess. It isn’t usually a problem on early corn, but can affect almost every ear of a late planting.

The good news is that corn earworm damage is mostly cosmetic and is usually confined to the tip of the ear. All you have to do is chop this off and the person eating the corn won’t even be aware there was a problem (if only all garden pests were so easy to deal with). Supposedly some varieties have tighter husks than others and so are less affected (i.e. Country Gentleman).

Diseases: Potential disease problems include: bacterial wilt, maize dwarf mosaic, corn leaf blights, root rot and rust.

Corn Smut (Ustilago maydis):

Corn smut is a fungus disease that infects corn plants, producing swollen growths on the ears. In the United States it is considered a pest and is destroyed whenever it occurs. In Mexico it is known as huitlacoche and is considered a delicacy that is actually worth more than corn. It has an earthy, sweet mushroom-like flavor and is said to be very good (I have never been lucky enough to get any to try).

Attempts have been made to popularize corn smut as a food in the United States by re-naming it Mexican truffle. Perhaps one day it will become a useful crop here too. I have no doubt high end restaurants would eat it up if you could grow it for them.

For culinary use this fungus should be gathered while it is still moist and immature, about 2 – 3 weeks after the initial infection. The mature fungus eventually releases a cloud of brown spores. If you are lucky enough to have corn smut, you could try collecting some of the spores. The Aztecs used to deliberately infect their plants with them and you could try doing the same.

Nutrient deficiency:

Nitrogen deficiency is common in corn, especially if the soil is cold or unusually wet or dry. Young plants will be spindly and their leaves will be pale and slightly yellow (rather than deep green). Treat it by feeding your plants compost tea or other high nitrogen liquid fertilizer.

Harvesting

Sweet corn:

When: More than almost any other crop, it is important to gather sweet corn at the right time. The ears mature from 17 – 23 days after pollination (depending upon the weather) and there are many indicators of maturity.

Sweet corn ripens quickly in warm weather, so watch it carefully and harvest when it is ready (it is only really good for a few days). If you can’t use it immediately, freeze it, or give it away. If not harvested at the right time it will be wasted.

How: Snap the ripe ear from the plant by pulling it downwards, being careful not to break the plant, or damage its neighbors.

Field Corn: Harvesting field corn is much easier than sweet corn; simply leave the ears until the entire plant turns brown and dry. Then remove the husks and dry the whole ears.

Watch for birds when the corn is ripe as they will sometimes strip seed from the whole ears. If they start to do this it is probably best to harvest immediately. You don’t want it to become a habit.

How to tell when sweet corn is ripe  

The silks wither and turn dark brown.  
The ear feels fat.  
The end becomes rounded rather than pointed.  
The ear tilts away from the stem.  

To check if an ear is ripe, pull open the top of the husk and squeeze a
kernel. If it is fat and spurts milky juice, it is ready. If it is dimpled and
spurts watery juice, it’s not yet ripe (just close up the husk). Be aware
that some super sweet varieties may have clear juice and still be ripe.   If the kernel is fat and tough, the ear is probably over-mature and will
be starchy and not very good.

You can also wait for raccoons to start eating it.  

Storage:

Sweet corn: Most types of sweet corn are best when used immediately and deteriorate quickly after picking. The super sweets can be stored for a few days in the fridge (the low temperature slows down the conversion of sugar to starch.

Field corn: The dry ears can be stored whole (they are quite decorative), but the seed takes up less space if you remove it from the ears. Make sure the seed is completely dry before storing it, otherwise it will go moldy.

Seed saving: Saving corn seed is a little more complicated than most other crops, because you have to worry about inbreeding (corn strains are very inbred). If you want to maintain a pure variety indefinitely you need to save seed from at least 50 plants (some say the absolute minimum is 100 with 200 being ideal) to maintain sufficient genetic variability.

If you are growing field corn this isn’t a big deal, you can just collect a few seeds from each mature ear and use the rest for food. It is a problem with sweet corn though, because you have to let the ears mature and dry fully to get the best seed. This essentially means you have to let one whole ear of sweet corn mature on each plant and only eat any others. Of course saving all of the seed from 200 ears is a huge amount of seed.

All of this makes keeping sweet corn seed pure and vigorous a special project, rather than an incidental activity. This is made even more difficult by the fact that sweet corn is quite short lived, so you can’t just do it once every few years. Saving sweet corn seed probably makes most sense as a community project, to be undertaken cooperatively by many gardeners (or by small commercial growers).

If you just want to save a little money on seed, you can forget about all I have just said. Just save the seed from a few ears and plant it the following year. The next year you could buy a packet of new seed and mix it with your own seed to deepen the gene pool. This isn’t ideal from a genetic standpoint, but what have you got to lose?

The other problem with corn is that it is wind pollinated and can cross very easily. To keep a strain pure you must either hand pollinate, grow only one variety at a time, or separate it from other tasselling plants by at least 250 yards (1000 yards is better). You should also collect your seed from the center of the stand, where there is less chance of stray pollen coming in.

Native Americans saved their own field corn seed for thousands of years, but they didn’t worry about the purity of a strain. In fact they encouraged diversity in their seeds, by collecting seed from a variety of plants, rather than simply the ‘best’, as we tend to do.

Hand pollination: This isn’t difficult, but takes some time, especially if you are pollinating 100 plants. The first step is to put a bag over the female flowers before the silks emerge, to prevent them being pollinated by any stray pollen. This must be taped shut, to prevent any pollen entering. The next morning, after the dew has dried, you go out and gently shake pollen from the newly opened tassels into a paper bag. Then simply transfer a little pollen onto the silks of each plant with a brush. You then replace the bags and leave them on until the silks go brown. Mark the ears carefully so they don’t get eaten accidentally (which would be a pain after all that extra effort).

Unusual growing methods

Early corn: If your growing season is short, or you just want to get very early corn, start your seedlings indoors a couple of weeks before the last frost date. It also helps to warm the soil under black plastic for a couple of weeks before planting out. Plant the seedlings on the last frost date and cover with row covers, or cloches, to keep them warm until the weather warms up.

Baby corn: These are the tiny immature cobs seen in Chinese restaurants. Any kind of sweet corn can be used, but there are special varieties (Baby Asian, Chires Baby Corn) that produce multiple ears per stem (Chires is said to produce up to 40 ears per plant).

Baby Corn is grown in exactly the same way as sweet corn, though you can plant it closer together (as close as 8˝ in fertile soil). The ears are harvested a couple of days after the silks show. As you might imagine this isn’t a very productive crop.

Dry garden: Field corn can be dry farmed using only the water that’s held in the ground. The plants must be spaced further apart for this to work. If you want to experiment with this then try and find a variety that was developed in a dry climate.

Three sisters  

Native Americans called corn, beans and squash, the three sisters and devised a very efficient method of growing them together. This works just as well today as it ever did and you may want to experiment with it. The corn stalks give the beans support, the squash creates a living mulch over the bare soil between the corn hills and the beans supply nitrogen. Even the foods they provide complement each other.

he corn is planted as described above, with 5 – 6 seeds in each hill. These are left to grow until they are about 10˝ tall and are then hilled up with soil to a height of about 6˝ (this makes them more stable). After hilling, 10 – 12 pole beans are planted in a circle around the growing corn, a few inches away from them. These sprout within 7 – 10 days. A week after they
have germinated, 5 squash seeds are planted around them, about a foot further out.

Once everything is growing there is little left to do, except ensure that they aren’t overtaken by weeds and have enough water. You may want to
help the individual pole beans find corn stalks to climb up. The squash
will eventually cover and shade the ground, though you might feel the
need to direct growing shoots to bare areas, so they fill in more evenly.  

Varieties

If you grow a lot of corn, you can save money by buying your corn seed in bulk from a farm supply store, rather in packets from the garden center. Of course you can also save your own open-pollinated field corn seed for use in future years.

Field corn

If you mention corn to a gardener, she will almost certainly think of sweet corn, as most of the corn grown by American gardeners is of this type. Yet in the history of corn as a food crop, field corn is actually far more important.

Field corn varieties can be divided into several groups, according to the type of starch they produce. There is also considerable difference in color, with blue, white, red and yellow varieties.

Dent Corn: Z mays var indentata

The kernels of dent corn have a depression in the middle (hence the name) and their starch is a mixture of hard and soft. Almost 80% of commercial field corn is of this type. Depending upon when they are picked, the kernels can be used for cornmeal, hominy, roasting corn or sweet corn.

Gourdseed corn is a type of dent corn that is prized for making high quality cornmeal.

Flint Corn: Z. mays var indurata

Flint corn grows better in cooler climates than most other types. The starch in the semi-translucent seeds is very hard, which is how it gets its name. It is used for cornmeal, though it is so hard it can be difficult to grind.

Soft Corn: Z. mays var amylacea

The seeds contain mostly soft starch hence the name. This type of corn is easily ground to meal and is commonly used for bread, tortillas and corn chips.

Popcorn: Z. mays var everata

Popcorn kernels have a very hard outer layer and a soft inner layer, a combination which makes them pop readily. They can also be used for cornmeal. Popcorn is a great crop for children to plant, as they get an extra special reward at the end of it.

Strawberry Popcorn – This is the easiest variety to find.

Japanese hulless – I have had good luck with this one.

Sweet Corn

Z. mays var saccharata

Sweet corn differs from field corn in that it is harvested while immature and most of its food is in the form of sugar rather than starch. This is why it is so sweet and why the seeds shrink when dried. It also makes the seeds somewhat temperamental in their germination capacity and accounts for their short storage life.

The sweetness genes in sweet corn are recessive so there must be a copy of the gene in both the flower and the pollen. If sweet corn is pollinated by field corn it will be starchy instead of sweet.

Corn is one of the few crops in which hybridization has made a big difference. Hybrids are superior to non-hybrids in that they mature more uniformly and are often sweeter. Unfortunately you can’t save the seed of a hybrid, as they don’t come true to type (of course you may not care as it isn’t the easiest plant to save seed from anyway). There are several types of sweet corn

Normal sugary (su) – Hybrids

The (su) gene is found in all older sweet corn varieties (open pollinated and hybrids) and its sugar starts to convert to starch soon after picking. These varieties aren’t as sweet as other types, but often make up for it with good corn flavor. These types do better in less than ideal conditions, such as cool soil.

Silver Queen F1 – Late season (90 days), sweet and tender. It was the standard corn for a while.

Honey & Cream F1 – Vigorous plants, sweet bicolor corn, a classic.

Normal sugary (su) – Open pollinated

Some traditionalists maintain that sweetness isn’t everything and that open pollinated varieties simply have a better corn flavor. If you grow them, you have to be more on top of things, as they don’t maintain their sweetness for very long. When harvesting you get to perform the boil water before harvesting ritual.

Country Gentleman – A shoe peg corn (kernels not in rows), a classic for roasting.

Golden Bantam – A favorite for 100 years.

Painted Mountain – Multi-colored and genetically diverse. Can also be ground to flour.

 Super sweet corn

These were bred for commercial growers, as they remain sweet for much longer than conventional varieties. They can be divided into 3 types, supersweet (sh2), sugary enhanced (se) and synergistic (sy).

Super Sweet (sh2): These contain the sh2 gene which not only makes them very sweet, but also means that their sugar converts to starch very slowly. It is important that they be fully mature before use, as they don’t develop much corn flavor until this time. They are known for being quite crisp in texture (some people call them tough).

These types don’t contain a lot of starch, which makes them somewhat temperamental to germinate in less than optimal conditions. They shouldn’t even be planted until the soil is at least 65˚F and preferably 70˚F. They also need to be isolated from other varieties while tasselling, otherwise the resulting kernels will be tough and starchy.

Honey ‘n Pearl F1 – One of best bi-colored sh2’s

Xtra-Tender F1– White super sweet.

Sugary Enhanced (se) (se+)

These contain a gene that enhances the normal sugary gene (su) and makes the kernels sweeter and more tender (some people think it is mushy). In addition the sugar is only slowly converted to starch after picking. These varieties don’t require isolation from other varieties.

Sugar Pearl F1 – An early white corn.

How-Sweet-It-Is F1– One of the sweetest corns around.

Kandy Korn F1 – Stays sweet for 2 weeks.

Sugar Buns F1 – An early (70 – 80 days yellow corn.

Synergistic (sy)

These varieties contain (su) (se) and (sh2) genes, which makes them both tender and very sweet. They also need to be isolated from other varieties when tasselling. They tend to be more vigorous than the sh2 types.

Montauk F1 – A bicolor (80 days).

Kitchen use

Traditional sweet corn begins to lose its sweetness as soon as it is harvested, because the sugar is gradually converted into starch. The sooner you cook it, the less sweetness will be lost. Corn epicures say you should have the water boiling before even picking your corn (and preferably out in the field on a camp stove). Sadly this wonderfully obsessive ritual is dying out because the newer hybrids stay sweet much longer (another unexpected way science makes our lives blander and more homogenized).

You can also cook corn in its husk on a barbecue or campfire.

Other uses: Corn has traditionally been used for bread, tortillas, mush, beer, whiskey and animal feed. It is now a major industrial crop, with thousands of uses from cornstarch to ethanol based motor fuel. It is also the source of the notorious high fructose corn syrup which finds its way into a huge number of processed foods.

Sweet corn chowder  

2 carrots
1 stalk celery
1 onion
1 sweet pepper
2 cups corn kernels
2 cups vegetable broth or water
1 cup potatoes
1 cup soy milk
1 tbsp flour
1 tbsp olive oil
Salt and pepper  

Saute the carrot, celery, onion and pepper in the oil for a few minutes
then add the water and potatoes and simmer 10 minutes. Add the corn
and cook for another 10 minutes. Then mix the soy mil, flour and salt nd pepper and add to mix. Simmer for another 10 minutes.  

Nixtamalization

This is the process of treating field corn to make a more nutritious and versatile food product known as corn masa meal. It is a fairly simple process, but somewhat time consuming.

Put 4 tbs pickling lime (calcium hydroxide) in 4 quarts of water and bring to a boil (wood ashes can also be used, though I’m not sure of the quantity). Then add 3 cups of washed dry corn and simmer until the skin of the corn kernels start to peel off (how long this takes will vary from 1 – 3 hours). Then take the pan off the heat, cover and leave overnight.

Next day you rinse the corn several times to remove all of the lime. The corn can then be ground to a coarse meal for immediate use or dried for later use. If you want a finer meal you have to remove the skins of the kernels too.

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