Minecraft wiki entry for Crop_farming, associated text: Later in the game, the highest yield per area of a given field may be more important than the fastest growth per seed. Fields sown solidly to achieve this with a single crop do grow at half the speed, but they also let you separate each type of crop into its own respective field and harvest one type all at once. However, one large field with alternating rows of different crops would still grow faster than smaller fields each sown solidly with a single crop.