The “Three Sisters” is a reference to the old Native American tradition of growing corn, pole beans and squash in the same plot or space. Each of these three crops help each other: The corn provides a structure for the pole beans to climb, so there was no need for poles. The beans provide nitrogen to the soil that the other plants can use. The squash vines spread out and shade the ground, helping to prevent the establishment of weeds. The squash leaves also act as a “living mulch,” which create a microclimate to conserve moisture in the soil. And the prickly hairs of the squash vines deter pests such as raccoons because they do not like to step on them. Coincidentally, corn, beans, and squash contain all eight essential amino acids, providing a complete protein when these plants are eaten together.
I do not know how far west into the Northern Great Plains these plants were grown but this was certainly a common practice east of the Mississippi, throughout the Midwest and as far west as the Mandan villages of central North Dakota along the Missouri River. Even though there is not much evidence that the Plains Indians, which inhabited our area in North Central Montana, grew these crops, I thought it would be interesting to try them out this summer. We see teepee rings on our land so I know the Native Americans lived here from time to time.
When it came time to plant, my main concern was that each plant would have enough room to gather water for itself without irrigation. We normally allow 54 square feet for each hill of 2 squash plants in our dry land production. Whereas the corn is allowed about 500 square inches per plant. In both cases this is about a third of the plant population recommended for irrigated fields or fields in the Midwest where they get about 3-times as much rain as we do. This means each hill of squash is about 88 inches from the next one on a grid and each corn plant is about 21 inches from each other. Because these plants were planted together, including the beans around the corn, I gave them a little more room than if I were planting them by themselves. The squash was planted on a grid every 93 inches with the corn in between on a grid of its own every 31 inches. The beans were a mixture of bush beans and pole beans, which I planted in combination from 0 to 4 beans around each corn plant. The beans were not planted until the corn was 6 inches high—about the middle of June. Unfortunately, we had no rainfall after the beans were planted and although most of them came up, they did not produce beans, nor did the pole beans climb up the corn. The corn and squash were planted on the 20th of May and they both produced adequate crops, despite the lack of water. The corn was divided into modern and heirloom Indian corn and for some reason, the modern sweet corn did not come up at all whereas the Indian corn came up uniformly.
Even though we have not harvested yet, we can already see that the corn and squash did not compete against one another too much for moisture and we cannot say anything about the beans because they did so poorly. That said, it was an interesting experiment even though the results were quite mixed. I would have planted the beans a week earlier, just before the last rain, if I had known it was going to be our last. In our area, maybe planting the beans when the corn is only 3 inches high would be better. Maybe I will try that next year.