A four to five year rotation plan is good for everything in the garden, it helps to avoid the buildup of soilborn problems. Think of plant families when planning your rotation. Tomatoes, potatoes, peppers and eggplants are all in the Solanaceae family, so think of them as one and don't plant them in the same soil year after year. Beans, peas, root crops, cabbage family, each one is a group, base your rotation on that and you'll be all set.