Corn is a common farm commodity. Varieties known as sweet corn are commonly grown by gardeners for home consumption and on a larger scale by market garden operations. There are also specialty corns, such as popcorn and ornamental corn, grown both by gardeners and in commercial operations. In small-scale gardens, the corn might be measured in simply by counting the plants. In large-scale operations, the planting rate per acre determines the amount of seed and potential yield.
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Common spacing of one sweet corn plant every 10 inches in rows roughly 36 inches apart yields about 17,000 corn plants per acre. Depending on the variety, this requires between 150 and 225 lbs. of seed per acre. Sweet corn planting density is lower than field corn density because it is commonly harvested by hand, which requires more space than with mechanized field corn harvesting equipment.
Depending on the hybrid or variety, field or grain corn planting rates vary from about 20,000 to 44,000 plants per acre. Grain corn dries on the stalk with the kernel forming a dent on one end when ripe, which is caused by shrinking starch. Higher planting rates require closer planted rows along with seeds planted closer together within the row. Higher planting rates are used for grain corn because the emphasis is on total yield rather than quality of each ear.
Farmers and gardeners are often limited by their seeding equipment. Row spacing ranges from 15 inches to 38 inches, although producers commonly choose single-row spacing and acquire the equipment designed for those requirements. This limits the actual range of corn plant density available to that producer.
The effect plant density on yield varies with the weather. If weather conditions are ideal, the highest plant density of corn per acre will have the highest yield. If the weather conditions are less than ideal, the high plant density may actually reduce yield. Corn prefers warm conditions with adequate moisture, from rain or irrigation, when growing and setting ears.