(News article for February 27, 2021; edited)
Sweet corn can be planted earlier than many other warm-season vegetables. In some years, planting as early as late February is feasible in southern Louisiana.
The growing point of corn remains below the soil surface for some time after seed germination, so a young corn plant can typically regrow if injured by a late frost. Planting a week or two before the last frost is an option if soil temperatures are at least 60 degrees F.
To extend the harvest season, additional seed can be planted every two to three weeks through April. For a fall harvest, planting can be resumed in July, but insect pressure is typically high at this time.
Corn requires a good deal of fertilizer to produce large ears. For every 100 feet of row (or 300 square feet), 5 pounds of 8-8-8 or 3 of pounds 13-13-13 can be incorporated into the soil before planting. Then, side dress plants twice, when they’re about one and two feet tall. Either 1 pound of 33-0-0, 1.5 pounds of ammonium sulfate, or 2 pounds calcium nitrate can be used each time, per 100 feet of row / 300 square feet.
Plant seeds about one inch deep and 10 inches apart within a row. Corn is wind pollinated, so plant several rows next to each other instead of one or two long rows.
There are several different types of sweet corn. Varieties like Merit (yellow), Silver Queen (white), and Sweet G90 (bicolor) are standard “sugary” (su) corn. These differ from field or grain corn in that kernels produce more sugar and less starch. They also have more of a substance called phytoglycogen that helps make corn creamy.
A disadvantage of normal sugary corn is that while it’s sweet at the time of picking, it loses its sweetness quickly after harvest as sugar is converted into starch.
A second type of sweet corn is sugary enhanced (se) corn. Like normal sugary corn, sugary enhanced corn has a high phytoglycogen content, contributing to creaminess, but kernels have higher sugar levels. Because of the higher sugar content, even though sugar is still converted into starch after harvest, sugary enhanced varieties have a higher sugar content for a longer time than regular sugary varieties do.
Sugary enhanced varieties include Ambrosia (bicolor), Argent (white), Avalon (white), Bodacious (yellow), Incredible (yellow), Miracle (yellow), Precious Gem (bicolor), and Temptation (bicolor).
The third group is “supersweet” (sh2) sweet corn. Supersweet corn has very high sugar levels, and this sugar is not converted to starch as quickly after harvest as it is in sugary and sugary enhanced corn. However, supersweet corn has less phytoglycogen and therefore a less creamy texture. Supersweet varieties include Cameo (bicolor), Honey N’ Pearl (bicolor), and Ice Queen (white).
There are now some varieties that combine two or all of these genotypes. Honey Select (yellow) is one example.
While all types of sweet corn should be grown away from field corn and popcorn, supersweet varieties also need to be at least 200 or 300 feet away from other types of sweet corn, to avoid producing starchy, tough kernels. Another way to isolate corn types from one another is to plant them at least 14 days apart.
If you’ve ever grown corn, you’re probably aware that corn earworms often make an appearance. To reduce the chances of finding one when you shuck your corn, an insecticide can be applied on a regular basis beginning when silks are observed. Insecticides containing spinosad, zeta-cypermethrin, permethrin, esfenvalerate, or bifenthrin have efficacy against caterpillars.
Alternatively, apply 15 to 20 drops (0.75 to 1 ml) of mineral oil to the silks on each ear, about 5 days after silks emerge.
Be sure that any pesticide you use is labeled for use on sweet corn, and read and follow label instructions.
The length of time it takes from planting until maturity depends on the variety and on temperatures. Expected days-to-maturity range from about 70 to 90 days. When sweet corn is ready to harvest, silks will be dry and brown. Harvest when a milky (sugary and sugary enhanced varieties) or clear (supersweet varieties) liquid runs from the kernels when they're punctured and before kernels are doughy.
Try to pick sweet corn the morning, when it’s cooler. If you aren’t ready to cook it immediately, refrigerate it.
Let me know if you have questions.
Contact Mary Helen Ferguson.
The silking stage is when measures are taken to prevent corn earworm damage. (Photo by Howard F. Schwartz, Colorado State University, Bugwood.org)
Sweet corn (Photo by Howard F. Schwartz, Colorado State University, Bugwood.org)