The Native Americans were very smart people. They understood plant need much sooner than modern science. Old timers understood companion planting too. Somehow though along the way this knowledge was pushed aside and forgotten. However, with the recent organic movement we have seen those seeking knowledge of the old ways. So that brings us to the three sisters: corn, beans, and squash. The name three sisters comes from the Iroquois legend of the the creation. To make the story brief Sky Woman who lived in the heavens became pregnant and then fell out of the sky. The animals saw her coming and took the earth from beneath the sea and made a soft place for her to land (North America). She gave birth to a daughter who later became pregnant herself with twins. She died during birth and Sky Woman buried her in the new earth. From her grave sprang three sacred plants: corn, beans and squash. These three plants first fed the twins and then the nations. So that is the story of the three sisters and why you will often in old timers garden see these three planted together. Scientifically, this is why they work well together. Corn depletes nitrogen in the soil, beans put nitrogen back in and squash has prickly, itchy vines and leaves to keep thieves away from the corn and beans. The beans also climb the corn and give it support and strength against the winds. This method of planting works much better with heirloom varieties since modern day GMOs are just pitifully weak and the corn cannot support the beans. I recommend heirlooms anyway and ban all GMOs in my garden. I plan on adding honey bees to my property sometime this year and GMOs kill off honey bee populations by rendering them sterile. Which by the way is what they are also doing to you and your children. So heirlooms are the way to go for healthy gardening. Back to the three sisters. There are several ways to properly plant this combination, here is one.
Wampanoag Method- This method was taught to the settlers of Jamestown, Va. and each family could sustain themselves with about an acre planted in this manner. First make small hills with a flat top and a lip around the edge about 4 inches high and spread about 4 feet apart. Then plant 4 corn seeds, 3 inches deep. When the corn is about 4 inches high, plant 4 bean seeds halfway down the hill. At the same time that you plant the beans, construct mounds 1 foot across and 3 in. high staggered among the corn and bean mounds. Then on top of each mound plant 4 squahs seedlings. Traditionally each seedling was placed in one of the cardinal directions on the mound. Along the north side of the garden plant sunflowers the same time as planting corn. The sunflowers are planted on the same mound as the corn and with 4 seeds also.
There are other types of three sisters gardens all using the same principles just different designs. It seems as if sunflowers were usually put along the north edge as well. Good luck and have fun.