The three vegetables compliment eachother in nutrition, soil health, and promotion of diversity.
Corn provides carbohydrates; beans provide fiber, protein, magnesium and iron; and squash provides Vitamin A, beta-carotene, and omega-3s.
The corn acts as a trellis for the beans that grow up its stalk and, in turn, the beans add nitrogen to the soil which is depleted by the corn- a heavy nitrogen feeder. The beans also help to stablize the corn stalk. The squash plant acts as a natural mulch, shading much of the soil around the corn and beans to prevent weeds and keep moisture in the soil. This method allows corn, beans, and squash to be planted without depleting the soil of all nutrients and requiring a cover crop or other means of nutrient additive to be implemented between seasons.
The Three Sisters method promotes diversity in crop production. When growing large fields of one crop, plants are susceptible to disease which, in some cases, can cause countrywide famine and starvation. An example of this is the Irish Potato Blight in 1845 where only one type of potato was grown and hence wiped out by disease. Nearly a million people suffered from starvation.
The Three Sisters are also famous for saving the lives of the pilgrims in Plymouth Rock. Tisquantum or "Squanto" introduced this method to the starving pilgrims in the 16th century and helped the foreigners thrive in the new land. Hence, the three vegetables became a staple to the pilgrims and the first Thanksgiving dinner included corn, bean, and squash-much to the tradition still held today.
Not only does the Three Sisters method look beautiful when planted in the garden, it also provides cultural heritage, nutrition, and promotes soil health and biodiversity. What an amazing trio!
Cornell University: Cooperative Extension and Department of Horticulture. A legend. http://blogs.cornell.edu/garden/get-activities/signature-projects/the-three-sisters-exploring-an-iroquois-garden/a-legend/
Cornell University: Cooperative Extension and Department of Horticulture. The need for diversity. http://blogs.cornell.edu/garden/get-activities/signature-projects/the-three-sisters-exploring-an-iroquois-garden/diversity/
Mann, Charles C. (2011). 1491: New revelations of the americas before Columbus, 2nd ed. Vintage Books: New York, NY.