Photos: Ron Patterson, UI Horticulture Educator
Corn is a warm-season grass and prefers temperatures between 60 – 80-degrees Fahrenheit.
After you have purchased your sweet corn seed, don’t get too anxious about planting it. Soil temperatures should be around 55 – 60 degrees for the seed to germinate well — test at noon about 2 inches deep. It only takes a couple of weeks for corn seed to rot in cold, wet soil. Soil thermometers are often available at farm stores or garden centers. Otherwise, you could plant your corn about a week before the average last spring frost date for your area.
Light frosts will damage young corn leaves, but as long as the growing point, which is below the soil surface in a young plant, does not get frozen, it will recover. Once the stalk starts to extend, a frost will likely kill the plant.
Corn is a heavy fertilizer user. Before planting, apply 2 – 3 pounds of a 10 – 10 – 10 fertilizer over 100 square feet of garden. Till or water the fertilizer into the soil.
Tilled soil should be allowed to settle for a couple of weeks so there is better seed-to-soil contact.
Corn seed should be planted:
one inch deep
9 – 12 inches between plants in the row
30 inches between rows
Because corn pollen moves by wind and gravity, it is best to have your corn patch be about four rows wide, rather than a single row. In addition, corn should be grown in full sun for a minimum of six hours, but more than eight hours a day, if possible.
Corn that is less than 85 days to harvest can be planted sequentially every two weeks until early-July in the warmer regions of eastern Idaho, mid-to-late June in the colder regions. This will provide a constant supply of sweet corn throughout the latter part of the summer. The same can be accomplished by planting corn with different days to harvest—the cultivars used should have the same sweetness gene (su, se, sh2, syn—see the April 17 post) to avoid cross-pollination of the different types.
Care after planting
Control weeds. Weed competition may reduce corn yields up to 50%. A light hoeing is best as deep cultivation can damage corn roots.
Corn should receive an inch of water per week during the hot summer days. In sandy soils you may want to spread that over a couple of irrigations each week. Try to avoid drought stress, particularly during pollination and kernel fill. Drought-stressed corn leaves will turn blueish and curl.
The second fertilization of half-pound ammonium sulfate (21 – 0 – 0) along 100 feet of row when the corn is about knee high, and a third fertilization of quarter-pound ammonium sulfate when the tassels first appear, will help improve yields. These later applications should be done as a side-dress — spread the fertilizer to the side of the row and rake in lightly, then water to move it into the root zone.
Corn earworm is the most common pest of corn. They do not overwinter in eastern Idaho, but travel on the wind. The nice thing about corn earworm is that it usually feeds on the tip of the ear which can be easily cut off when the corn is harvested.
Sweet corn is an easy crop to grow in the home garden. Plant your sweet corn in mid-to-late May and enjoy the sweet crunch of corn-on-the-cob later this summer.
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