Sow sweet corn seed in full sun when the soil warms to between 60 and 95 degrees Fahrenheit. Sweet corn does not germinate well in cold soil and in low temperature will die. Sweet corn seeds can appear shrunken and shriveled; before they can germinate, they must slowly plump up with water. To help them along, soak dry seeds in water at room temperature overnight before planting (Image 1).
More Planting Tips: In the warmer climates, direct-sow seeds in mid-May: The cobs should be ready for picking in late August or September. In cooler climates, sow the seeds under glass in mid-April to early May, then plant out in late May to early June.
Any seedling transplants should be started in peat pots three weeks before you are ready to set them out (Image 2). To start seedlings indoors, sow 2 seeds — each about an inch deep — in 3" peat pots. To help them germinate, keep the room temperature at a gentle heat of 55 to 59 degrees Fahrenheit. Once they've germinated, use a cool-white fluorescent grow light to aid their growth: place the light about 2" above the plants. Leave the light on 12-14 hours a day and be sure to raise it as the plants grow.
Before transferring seedlings outdoors, harden them off by gradually acclimating them to outside conditions. To do this, place the seedlings outside during the day when temperatures are above 40 degrees Fahrenheit; do not set the plants in direct sun or high wind. Set them wherever there's shade. Move them out a bit more each day for greater exposure to the sun. Each night, bring the plants indoors. Provided they are at least 2" tall, after three to five days of hardening off, they'll be ready to transplant outside.