Alfalfa is a perennial crop, which means it will grow for several years after planting. Alfalfa is planted in the spring or fall. Since the seeds are so small (1-2 millimeters), slightly wider than the tip of a pencil lead, they must be planted close to the surface of the soil. Between 15-25 pounds of seeds are planted per acre, which is about the size of a football field. There are about 200,000 alfalfa seeds per pound.