Growing Great Organic Corn
There are few things that truly celebrate the summer sun more than a fresh harvested ear of sweet corn. This precious treat, along with the dent, milling and popcorns, is a true nod to what the summer heat and thunderstorms can bring. Corn is a warm-season tender annual that requires high soil fertility to produce uniform ears. Considered a cereal grain in the grass family, corn was first domesticated by indigenous communities in southern Mexico about 10,000 years ago. Since that time, it has been bred and developed in relationship with its human stewards on every continent. Today, corn is a serious draw at the farmers market and at farmstands and makes a great addition to the home garden.
While corn is not necessarily a difficult crop to grow, there are a few strategies that can help the plants reach their fullest potential. Below we'd like to highlight some tips on growing a great organic corn crop.
Choose productive organic varieties
When it comes to growing corn organically, one of the most important first steps is selecting a variety that has been bred to succeed in organic production. As you probably know, conventional corn is a big industry and the seed that is utilized in that system is oftentimes not the best choice for your home garden or organic farm. At High Mowing, we have an excellent selection of non-GMO corn varieties that have proven to yield abundantly when grown in an organic system, without the need for synthetic fertilizers, herbicides and pesticides.
White Sweet Corn
Natural Bright XR F1 74 Days
Mirage F1 79 Days
Yellow Sweet Corn
Fisher's Earliest 70 Days
Bi-Color Sweet Corn
Allure F1 75 Days
Enchanted F1 78 Days
My Fair Lady F1 78 Days
Who Gets Kissed? 78-84 Days
Popcorn, Ornamental and Milling Corn
Tom Thumb Popcorn 85 Days
Painted Mountain Milling Corn 90 Days
Dakota Black Popcorn 95 Days
Direct Seed or Transplant
Corn can be grown on any scale and often times the quantity planted will depend on the equipment available to manage it. In the home garden and on the small-scale market farm, corn can be grown as a transplant. This allows the grower to control the germination of the crop, gives it a head start earlier in the season, and gives the plants a real shot at competing with weeds and crows. This can be especially beneficial in northern territories where the summer season is short. Corn should be seeded in cells, 1-2 kernels per cell, and transplanted out 10-14 days after seeding after threat of frost has gone. If plants become rootbound, they will be unable to grow to maturity and produce full ears.
Direct seeded corn should be sown 1 inch deep, 8-14 inches apart in rows spaced 24-48 inches apart (depending on cultivation equipment,) just past the last threat of frost. Corn will not germinate in soil colder than 50 degrees Fahrenheit and will grow best when the soil temperatures range from 60-85 degrees Fahrenheit. Planting corn too close together can cause plants to produce small ears much later in the season. Corn prefers a well drained soil with a pH of 6-6.8 with plenty of organic matter. Water is essential to grow a healthy corn crop and is especially important just a week or two before the corn begins to produce silk.
In order for corn to have proper pollination, corn should be planted in blocks. Corn is wind pollinated and planting your corn in blocks as opposed to in long rows can prevent some of the negative affects of improper pollination, like uneven ear and kernel development. Due to the potential of cross pollination through wind, it can be important to buffer an organic corn field from local conventional fields to prevent the genetic drift of GMO material. Planting your field, dent, milling and popcorns away from your sweet corns will prevent cross pollination in your own patch.
Manage Your Soil Fertility
Corn is traditionally considered a heavy feeder and this is due to the high levels of nitrogen, phosphorus, potassium and zinc needed to produce a healthy crop. In an organic growing system, utilizing a legume cover crop ahead of the corn crop can help boost nitrogen needs. Fertilizing at the time of planting and side dressing the corn when it is 1 foot tall and once again when it tassels with a nitrogen fertilizer such as blood meal, fish products, alfalfa meal, aged chicken manure, cottonseed meal, (among many other regional options), can also help to ensure that the corn has what it needs to grow. If your nitrogen source is chicken manure, you may not need to apply additional phosphorus.
Low potassium in a soil can be problematic for corn development and is commonly a problem in a dry year. Symptoms of low potassium in your corn crop are a yellowing of the outer leaf margins. Symptoms begin at the leaf tip and move to the leaf base. Potassium deficiency symptoms are similar looking to nitrogen deficiency, but there is a key difference. Nitrogen deficiency, which first appears as yellowing on the older leaves, is located from the leaf tip down the midrib in a V shape. If potassium deficiency persists in a corn crop, it can lead to the reduction of plant health and eventual lodging of the stem during wind events. Potassium is an essential aspect of keeping plants healthy during times of stress.
Some good options for increasing potassium in your soils include greensand, hardwood ashes, kelp meal, alfalfa meal, and sheep manure, among others. Buckwheat cover crops are excellent miners of minerals and can bring normally unavailable potassium and phosphorus up from the subsoil (along with many other micronutrients,) and make them available for future crops.
A lack of phosphorus in a corn crop will present as a stunting of the plants. They will appear dark green in color which may make them appear healthy at first, but the plants will reduce in size and remain small. Older leaves and the stem may show signs of stress such as purple and/or yellow coloration. Phosphorus is important for root development, stem formation, and fruiting. Sources of organic phosphorus are most commonly derived from rock phosphates, bone meals and colloidal phosphate or what is known as "soft phosphate" sources. While the rock powders are cheaper and longer lasting, bone meals are more readily absorbed by the plants.
Zinc is naturally occurring in most growing spaces and is made available as rocks degrade in the soil. How much zinc is available in a soil will depend on the parent material of the minerals and rocks of your soil type. Zinc is an important player in the metabolic activity of your crops. Zinc deficiency in corn will present as a white or yellowing of the youngest leaves of the crop. This begins at the leaf base and does not extend to the leaf tip. High soil phosphorus can prevent zinc from being taken up by your crop. Zinc deficiency can be a problem in wet and cloudy years. Soils that have low organic matter can often have a limited store of available zinc. Adding compost to your growing spaces can go a long way in increasing zinc availability in your soils. There are other OMRI listed zinc applications, included chelated zinc sources, that can be used when the deficiency is more severe.
Don't Let Weeds Compete
One of the most important aspects of growing a healthy corn crop is keeping it weed free. Young weeds and corn are extremely competitive with each other for water and available nitrogen. Weeds grow very well in corn crops because these two things are generally found in great supply. When planting a corn crop, it is important to start with a weed free bed. Just as the corn germinates in the soil, or a week after the corn plants have been transplanted, it is important to cultivate the soil surrounding the plants to displace the newly growing weeds that may be invisible to the eye, but are very much present and in what is known as their "thread stage." This process should be repeated each week to prevent further development and competition.
Weeds that have grown even taller and have reached 3-4 inches in corn of the same height must be removed to prevent potential crop loss as weeds will rapidly grow beyond corn at that stage. If the early weeds are controlled and the corn plants are able to develop into healthy stalks, they will eventually shade out weed pressure and move into high productivity.
Pests and Diseases
Some common insects pests of corn include: Soil Cutworms, Spider Mites, Corn Leaf Aphids, Thrips, Corn Rootworms, Corn Leaf Hoppers, Stalk Borers, Corn Flea Beetles, Southern Corn Leaf Beetles, Wireworms, Seed Corn Maggots, Chinch Bugs, and White Grubs. Some insects, especially Aphids and Leafhoppers can transmit viruses to your corn crop. Weed control, especially weed pressure from plants like Johnson Grass, can help prevent dense populations of these pests and the spread of disease.
Some important corn diseases include: Anthracnose, Bacterial Leaf Streak, Rhizoctonia Root Rot, Bacterial Stalk Rot, Northern Corn Leaf Blight, Common Rust, Southern Rust, Eye Spot, Fusarium Stalk Rot, Fusarium Root Rot, and Gray Leaf Spot. Diseases in corn can be caused by a lack of nutrient availability leading to stress, over wet and/or cool growing conditions, and/or plantings that are too dense or weedy, limiting airflow.
An interesting pathogen of corn, is Corn Smut. Corn Smut is a plant disease caused by the pathogenic fungus Ustilago maydis. This fungus grows on corn and is edible, considered a delicacy in Mexico called huitlacoche. The infected plants produce kernels that swell up into mushroom-like tumors. Corn Smut is also called Corn Truffles, and has many culinary applications. Of course, as a pathogen, this fungal infection can affect the productivity of your corn patch if it is aggressive and left unchecked.
Harvest Right On Time
Harvesting sweet corn is a bit of an art form, much like harvesting melons and watermelons, and it takes experience to perfect your harvest timing. If you are harvesting sweet corn from the garden, you can meticulously inspect each ear to ensure it is picked right on time. In a larger patch, you will need to inspect ears here and there before you make the call to grab your bounty from the patch. Some tell-tale signs of a ripe sweet corn patch include: full feeling ears that are plump to their ends, brown silks, and kernels that have gone into the milk stage.
You can tell when sweet corn has entered the milk stage when kernels burst when punctured, releasing a milky, sweet liquid. If you puncture the kernel and no liquid comes out, you have waited a bit too long. Sweet corn is generally ready 20 days after it first entered its silk producing stage. Sweet corn is best harvested early in the morning when the sugars are concentrated and, at maturity, they should easily twist off the stalk.
For your dried corns, like your milling and popcorns, the harvest looks a bit different. These corns need to develop and dry in the fields entirely before picking. At the time of harvest, all of the kernels on the ear should be firm and the husks should be dry. The ears should be harvested and stripped of their husks. Placing them in a mesh, breathable bag and hanging them in a warm, dry place will allow the ears to properly cure for storage.
You want your kernels to dry, but not too much. If kernels get too dry, they will lose their nutritional value and will not cook down or pop well for popcorn. Once the ears are cured and stabilized, they can be stored in air-tight containers on the ear, or shelled for later use.