Corn, beans, and squash were known as the Three Sisters and were planted together on a small mound in a traditional garden that formed a community of plants. In this natural relationship, the corn provided a ladder for the beans to climb, the beans helped replace nutrients that the corn and squash took from the soil, and the squash vines crowded out many weeds, kept erosion to a minimum, and increased the amount of rain that soaked into the soil. Many traditional farmers also set fires after the harvest to clear away dead plants for a new crop, leaving nitrogen-rich ashes that helped the soil. Through such methods, Native Americans found it possible to get 15 years or more of continuous yields from the ground before its fertility was used up and new land had to be cleared.