Fertilizer application for sweet corn happens at planting when the plants have four to six leaves, and again when the plants have 10 to 12 leaves. Corn is a heavy feeder, meaning it needs multiple applications of fertilizer to support the tall growth of the plants.
The specific type and amount of fertilizer depends on the specific soil in the garden. Local extension offices typically perform soil tests to give specific recommendations. The initial fertilizer goes into the soil before the corn seeds. Working the fertilizer into the soil helps make it readily available to the seeds as the corn plants begin to grow.