If there is one vegetable that truly says "summer," it's corn. A freshly picked ear of corn, its sweet, tender kernels dripping with butter, is a seasonal treat we associate with long, hot days, picnics and barbecues, and the bounty of the midsummer garden.
This native member of the grass family has been cultivated in our hemisphere since before Columbus first saw it growing on the island of Hispaniola in 1492. It has undergone a lot of breeding changes since then. Thanks to a recessive gene that keeps all its sugars from converting to starch as it matures, we now have the delicious "sweet" varieties that we so enjoy eating fresh in summer.
Sugary, Sugary Enhanced, Supersweet or Synergistic?
The characteristics of each kernel of corn come from the genes of both the plant that produces the ear and the pollen that fertilized it. The genes that give corn it sweetness are recessive, meaning that the genetic contribution from both parents must contain genes that code for sugar formation. (The field, or dent, corns have dominant starch-producing genes.)
Standard sweet corn varieties contain the sugary (SU-1) gene that gives them their sweet taste and creamy texture. But the sugars in these varieties begin changing to starch as soon as the corn is picked. These traditional varieties are responsible for the old saying that you should have the water boiling in the pot before you head out to pick the corn.
Sugary enhanced (SE) hybrid varieties have a gene that increases both sugar content and tenderness and creaminess, compared to the standard varieties. Because of their enhanced sugar content, SE varieties stay sweeter longer than standard sweet corn, especially if they are kept at cool temperatures. So gardeners have a little more flexibility when it comes to harvesting and cooking the corn. Heterozygous hybrids have one copy of the SE gene, with about 25 percent sugary enhanced kernels, while homozygous hybrids with two copies of the SE gene are extra sweet, having 100 percent sugary enhanced kernels.
Supersweet corn carries the SH-2 gene that dramatically slows the conversion of sugar to starch in the kernels, so ears remain sweet for many days after harvest. Because even the mature seeds contain so little starch, they can be harder to grow from seed. Most of these varieties must also be be isolated from plantings of standard and sugary-enhanced varieties to avoid cross-pollination that can result in starchy kernels.
Synergistic (SYN) hybrids really go to town genetically in the sweetness department. They contain not only SU-1 and SE genes, but the SH2 gene from supersweet corn as well, a combination that results in tender kernels with a very high sugar content that has a very slow rate of conversion to starch.
Tips for Good Germination Corn likes it warm, so don't be in a rush to get your seeds in the ground. Wait until the soil has really warmed up and all danger of frost is past, usually about two weeks after the last frost date in your area, before tucking seeds in the ground. This is especially important when planting supersweet varieties.
Planting Because corn is wind-pollinated, it should be planted in blocks of at least four rows rather than in long single rows. Leave 2 to 4 feet between rows, sowing the seeds 1-1/2 to 2 inches deep and 6 to 8 inches apart. By planting early, mid, and late-season varieties you can extend the harvest over several weeks. Plant corn on the north side of the garden to prevent it from shading nearby crops.
Corn requires a good deal of nitrogen for optimum growth, so work plenty of aged manure into the soil the previous fall and plan to fertilize with additional nitrogen during the growing season if necessary.
Care Thin the corn to stand 12 to 16 inches apart when the plants are 4 to 5 inches tall. Provide at least 1 inch of water a week. Control weeds with frequent shallow cultivation until the plants are knee high. Then apply a 3- to 5-inch layer of mulch. Watch for signs of nitrogen deficiency (yellowing leaves) and respond with quick side-dressings of a nitrogen-rich fertilizer such as fish emulsion.
Harvest Sweet corn should be harvested when its ears are completely filled out and a pierced kernel shows a milky white liquid. Another sign that corn is ready for picking is when the silks have turned brown but are still damp to the touch. Use a downward twisting motion to pull the ears from the plants.
Question of the Month
Worms in the Corn
Q: When I harvested my ears of corn, there were caterpillars eating the kernels at the tip. How can I control these pests organically?
A: Those caterpillars munching on your corn are corn earworms. These pests may also be found on other crops in the garden. When they are tunneling into tomatoes, they are known as tomato fruitworms. They are also known to attack peppers. No matter what you call them, these striped yellow, brown or green worms can attack corn plants in all parts of the country.
To control them without pesticides, place five drops of vegetable oil at the base of the silks, right next to the husks, once the silks are fully extended and have begun to turn brown. This will smother any earworms as they try to enter the ear.