"In late spring, we plant the corn and beans and squash. They're not just plants- we call them the three sisters. We plant them together, three kinds of seeds in one hole. They want to be together with each other, just as we Indians want to be together with each other. So long as the three sisters are with us we know we will never starve. The Creator sends them to us each year. We celebrate them now. We thank Him for the gift He gives us today and every day." - Chief Louis Farmer (Onondaga)
The "Three Sisters" method is a form of companion planting using corn, beans, and squash. Although this method originated with the Haudenosaunee, these three have been planted by many traditional Native American gardeners throughout North America.
The beauty of this method is that each vegetable benefits from the others. Corn gives the beans a place to climb, the beans provide nitrogen to the corn roots and the large squash leaves provide shade and living mulch which helped to deter weeds and hold moisture in the soil.
To begin, you need to make mounds to plant the corn in. They should be about 1 1/2 feet across on the top. The center of each mound should be 5 feet apart from the center of the next. The mounds should be staggered in adjacent rows, making up an area at least 10 ft. by 10 ft. This will ensure that the corn pollinates properly. First, plant four corn seeds in a diamond on top of the mounds. They should be about 6" apart.
When the corn is about 4" tall, you can plant the beans and squash. Plant the beans in a square shape in between the corn.
Build your squash mounds the same size as the corn/bean mounds. Build them in between each corn/bean mound. Plant 3 squash seeds, 4” apart in a triangle in the middle of each mound. Once these squash seedlings emerge, you can thin them to two plants per mound.
This diagram is from http://www.reneesgarden.com/