Page 5 of 5 of the Sweet Corn Guide

Sweet Corn: Pollinating and Fertilizing

Author: Julie Baka

Example of poorly polinated corn Example of Bad Pollination

When all the conditions are right (adequate drainage, ample moisture, full sun and good, weed-free soil), a sweet corn plot would seem to have all it needs to produce plump, delicious ears. Two other things may be necessary, though, for a bountiful crop – fertilizer and hand-pollination.

Remember, corn plants need a lot of nitrogen and are pollinated by the wind. All plots likely will benefit by a boost of fertilizer. Hand pollination, however, is only required for very small plots of corn or if just one to three rows of corn are planted. As a wind-pollinated plant, nature does an amazing job of pollinating corn when it is grown in thick plots and large numbers of rows.


Pollination

How Corn is Pollinated

shows how pollen falls on ears How Pollen Falls Onto Silks

Hand-pollinating corn is actually quite easy. But, before we get to the do-it-yourself steps, below is a basic explanation of how corn is pollinated.

There are two parts in corn’s pollination process:

  1. the tassels which produce the pollen
  2. the corn silks which transport the pollen down to the individual kernels

Tassels - Each corn tassel produces half a million pollen grains a day, so there are few worries about adequate contact of pollen with the silks. The pollen falls from the tassels by wind to the silks on the ears below. Each plant can self-pollinate. Pollen does not have to go from one plant’s tassel to a different plant’s silk. They also can pollinate from one plant to another. (See our how to choose the best sweet corn article to learn the importance of isolating plants to prevent cross-pollination of different varieties.) See the moisture estimate chart in our corn-planting article if you are unsure if you are over- or under-watering. (link to moisture chart in corn planting article)

Silks - The sticky silks grow 2.5 to 4 centimeters (3/4 to 1 1/2 inches) per day in optimum conditions, starting at the base of the ear. They will continue growing until they are pollinated. When pollen enters the silk tube, it takes about 24 hours to travel to the seed and begin forming a kernel of corn. After fertilization, the silks dry out and turn brown. These silks are your best visual indication of when corn is ready to harvest. They will be brown and mostly dry.

Hand Pollinating Corn

Pollination by hand Hand Pollination with a Brush

When the white silks emerge from the husk, it is time to ensure the pollen gets to the ears. The simplest way to do this is to walk through the corn plot twice a day for at least three days. While walking, simply bump and slightly shake each plant so that pollen falls down onto the silks.

To be more precise, place a sack under the tassels and shake the pollen into the sack. Dip a paint brush into the pollen in the sack and then gently paint the pollen onto the silks. Repeat this procedure for 3 days on every ear of corn.

In about 24 hours, you will know if your corn has been pollinated because the silks will begin to dry out and turn from white to brown.



Fertilizer

Fertilizing Sweet Corn for Best Growth

As a fast-growing leafy crop, corn is generally low-maintenance. However, a dose of nitrogen will help raise the level of nutrients in the soil to help create a beneficial environment for corn. For tall healthy stalks, corn enjoys a nitrogen-rich soil environment with enough phosphorus.

Before Planting Corn Seeds

  • Spread a 2-inch layer of compost over the corn plot area. Compost not only adds nitrogen, but also various micronutrients, while improving drainage and enhancing the soil structure.
  • Lightly sprinkle nitrogen fertilizer, organic if available, over the layer of compost. Organic nitrogen supplements may include fish meal, cottonseed meal or blood meal.
  • Using a garden spade, or a grub hoe, mix the compost and fertilizer with the soil until the mixture is about 4 to 6 inches deep.
  • Plant the seeds according to planting instructions for your corn variety and layout.

As the Sprouts Grow

  • Fertilize the plants with a 16-16-8 liquid fertilizer when the corn plants have reached a height of 4 inches, but before it reaches 8 inches tall.
  • side dressing by hand Side Dressing with fertilizer
  • Also add a few inches of organic mulch when the corn is 3 or 4 inches tall. Mulch helps conserve water in the soil and helps ensure consistent soil moisture levels that corn plants need. It also attracts earthworms and adds nutrients as the organic matter decomposes and gets incorporated into the soil.
  • Fertilize the plants again when they are about 10 inches tall. This is best done by side-dressing, rather than applying fertilizer directly on the young plants. For this application use a 46-0-0 (all nitrogen) fertilizer product. Spread the nitrogen in a line on the soil surface about 6 inches from the row of corn. Water the corn as usual to help carry the nitrogen down to the root systems.
  • Add nitrogen one last time once the sweet corn ears begin producing silk, using 46-0-0 nitrogen fertilizer according to product application directions.

Understanding Fertilizer Numbers

The numbers on fertilizer containers simply indicate the ratio of nitrogen, phosphorous and potassium (NPK Values) in the product. Unlike general all-purpose fertilizers such as a 15-15-15 product used on lawns, a 16-16-8 fertilizer has a higher level of nitrogen and phosphorus compared to potassium. By comparison, general vegetable garden fertilizers have an NPK value of about 4-3-3.

N - Nitrogen is responsible for producing leaf growth and is the main chemical involved in photosynthesis.

P - Phosphorus (Phosphate) aids in plant maturity, supports the vigorous development of roots, stems, blossoms, and fruits.

K - Potassium (Potash) strengthens the overall plant, providing resistance to disease and reduces plant stress. Aids in early growth, stem strength and improves the color and flavor of fruit.

NOTE: Plants reveal through their overall health, color, size and vitality if they are receiving too much or not enough nutrients. See the nutrient deficiency section below to learn more.

Organic Fertilizers

For those who prefer to enhance their corn’s growth naturally, below is a chart illustrating the nutrients in various natural sources.

  • Bonemeal
    • Contributes Phosphorus 20 - 25%
    • It is very slow acting. It will not burn roots.
  • Compost
    • Organic matter, varying proportion of all nutrients
    • The best all-round organic fertilizer; should also be used with chemical fertilizers
  • Cottonseed meal
    • Nitrogen, 6-9%; Phosphorus 2-3%; Potassium 1.5-2%
    • Low PH, good for acid loving crops
  • Dried blood and tankage
    • Nitrogen, 5-12%; phosphorous, 3-13%
    • One of the best organic sources of nitrogen, aids growth of soil organisms. Quick acting.
  • Fish meal and fish emulsion
    • Nitrogen,6-8%; phosphorous, 13%; potassium, 3-4%, trace element
    • Quick acting.
  • Horn and hoof meal
    • Nitrogen, 7-15%
    • Quick acting.
  • Fresh cow manure
    • Nitrogen, 0.6%; phosphorous, 0.15%; potassium, 0.55%; organic matter
    • Relatively low in nitrogen. Can be used directly on garden with out aging
  • Dried goat or sheep manure
    • Nitrogen, 2.5%; phosphorous, 0.25%; potassium, 1.5%; organic matter
    • Has higher nitrogen than most manures. Needs to be aged or composted at least three months before using on the garden
  • Fresh Horse manure
    • Nitrogen, 0.7; phosphorous, 0.25%, potassium, 0.55%; organic matter
    • Needs composted at least 6 weeks prior to use on the garden to kill seeds.
  • Dried poultry manure
    • Nitrogen, 4.5%; phosphorous, 3.2%; potassium, 1.3%; low in organic matter
    • highest manure in nitrogen level. Do not use directly on plants, as it may burn them.
  • Fresh rabbit manure
    • Nitrogen, 2.4%; phosphorous, 1.4%; potassium, 0.6%; organic matter
    • Needs to be aged or composted at least three months prior to using in the garden
  • Rock phosphate
    • Phosphorous, 24-30%
    • Slow acting, non-burning
  • Dried Seaweed
    • Nitrogen, 1-2%; phosphorous, 0.75%; potassium, 5%; organic matter
    • This is a good soil conditioner because of its hight content of colloids, which retain nutrients
  • Sterilized sewage sludge
    • Nitrogen, 4-6%; phosphorous, 3-4%; trace potassium and elements; organic matter
    • May contain heavy metals that build up in the soil over the years
  • Wood Ashes
    • Phosphorous, 1-2%; potassium, 3-7%
    • An old time standard. Has an alkaline effect on the soil

Corn Deficiency Problems

deficiency guide Nutrient Deficiency Signs

Nitrogen (N)

Nitrogen is necessary for above ground growth of plants and is considered one of the most important nutrients. It is the most important nutrient for corn, a member of the grass family. Nitrogen is used to make proteins that build cell material and plant tissue, promoting growth of the stems and leaves which is especially important for leaf crops such as cabbage, lettuce and spinach. In addition, it is necessary for the function of other essential biochemical agents. Of all the major plant nutrients, Nitrogen is often the most important deciding factor in plant growth and crop yield.

Excess nitrogen can also cause problems by producing excessive vegetation in certain crops where excessive leaf development is detrimental to the crop in reducing the quality of the root, fruit or flower.

Nitrogen Deficiency Symptoms

Nitrogen deficiency causes stunted or slow growth, slender fibrous stems and the classic yellowing of the leaves. Younger leaves remain green longer, because they receive soluble forms of nitrogen transported from the older leaves. This usually causes the yellowing, and in severe cases, dropping of the leaves.

Phosphorous (P)

Phosphorus helps plants transport and assimilate nutrients and is a major building block in all living plants. It is responsible for storing energy. The stored energy allows for transporting nutrients across the cell walls of the plant. Good phosphorus levels ensure crops will reach their full potential for healthy development of fruit, flowers and seeds. Phosphorus helps to build plant vitality and is of special importance in developing strong root systems that ensures better resistance to root rot diseases.

Phosphorous Deficiency Symptoms

Phosphorous deficient plants are usually dwarfed and spindly. The leaves, in contrast to those lacking nitrogen, are often dark green with purple tints. The undersides of leaves are reddish or purple. Leaf veins and margins often turn bronze. Deficiency symptoms occur first in more mature leaves. Fruit development is usually delayed.

Potassium (K)

Potassium enables plants to develop strong, thick stems, healthy roots and large, plentiful fruit. Plants require larger quantities of potassium than any other nutrient. Potassium is associated with movement and retention of water, nutrients and carbohydrates in plant tissue. It stimulates early growth and hastens maturity. Potassium is a key nutrient in the plant’s tolerance to stresses such as cold-hot temperatures, improves resistance to pests and diseases and is essential for the development of fruits, flowers and seeds.

Potassium Deficiency Symptoms

As with nitrogen and phosphorus, potassium is easily redistributed from mature leaves to the younger ones. Therefore deficiency symptoms will appear first in the older leaves. These become ash-gray colored instead of deep green, will look scorched at the edges (marginal chlorosis) and start to crinkle or curl with mottled yellow tips that later turn bronze.

Plants deficient in potassium often develop weak stem and stalks, small fruit and shriveled seeds, along with poor growth and yields. They also become susceptible to disease.


Final Tips for Growing Corn

  • The small offshoots, or suckers, should not be removed from the plants. Generally, the yield will be better if the offshoots are permitted to remain, even though they do not produce ears.
  • Cultivate to kill weeds weekly until the corn plants are tall enough to shade weeds and prevent their growth.
  • Harvest the ears when the silks are brown and a milky juice spurts from the kernels when punctured with a thumbnail. Cook them immediately or prepare to preserve the crop by freezing or canning. Corn’s sweetness and nutrients are lost soon after picking, which varies slightly by variety.



Now that you know pollination and fertilization, go back to our first article in this Guide to make sure you are growing the right variety for your conditions.

Click a page below to read the rest of our Sweet Corn Guide




Sources:

  • The Vegetable Encyclopedia and Gardeners Guide by Victor A. Tiedjens; 1943
  • Woman’s Home Companion Garden Book by John C. Wister; 1947
  • Giant Book of Garden Solutions by Jerry Baker; 2003
  • Reader’s Digest Back to Basics: How to Learn and Enjoy Traditional American Skills; 1981
  • BetterVegetableGardening.com: What is NPK Fertilizer