Sweet corn is a warm-season annual grass grown for its sugary kernels, picked at the milk stage when a punctured kernel runs milky. The sugar turns to starch within hours of picking, which is why home-grown corn, eaten the day it is cut, is worth the space it takes.
Corn is wind-pollinated, so plant it in a block of at least four short rows rather than one long row, or the ears come half-filled. Sow directly once the soil has warmed to 60°F, a week or two after last frost, an inch deep and 8 to 12 inches apart, and sow a second block two or three weeks later for a longer season. It is a heavy feeder: work in compost before sowing and side-dress when the plants are knee high. Water deeply during tasseling and ear fill, when a dry spell costs the most. The roots are shallow, so hoe lightly and mulch rather than cultivating deeply.
Pick when the silks have browned and dried, about three weeks after they appear, and the ear feels full to the tip. Raccoons and deer find corn the night before you do; a fence or an electric wire is the only reliable answer. Corn earworm enters at the silk end; a drop of mineral oil on the silks as they start to brown limits the damage.
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.
Corn Smut
Swollen grey-white galls on ears, stalks, or tassels that rupture into masses of black powdery spores.
Cut out and bag galls before they rupture; do not compost. Avoid plant injury, rotate crops, and remove infected debris at season end.
Northern Corn Leaf Blight
Long, cigar-shaped grey-green to tan lesions on leaves, starting on lower foliage and spreading upward in wet weather.
Plant resistant varieties, rotate away from corn for two years, and remove crop residue. Improve airflow and avoid overhead watering.