The sisters are corn, pole beans, and squash. Planting these three plants in the same growing area follows an historical method, attributed to Native Americans, that optimizes the synergistic relationship between them. Individually they require a lot of space: corn is wind pollinated and needs a large block of space in your garden to sustain the number of plants required for efficient kernel development; beans need a trellis support system to keep them off the ground so they can be harvested easily; squash spreads rapidly and blankets a large area. Planted separately these three crops can encompass an entire garden, but when planted as sisters the space required drops dramatically.
Traditionally the sisters are planted in that order. Four to seven corn seeds are planted in late spring a few weeks after the last frost date in the center of a two- to three-feet wide, low, flattened, round mound. Additional mounds are placed about four to five feet apart on center. When the corn is about 6 inches tall, 6 to 10 bean seeds are planted in each of those mounds about 6 inches away from the base of a corn stalk. After the beans sprout, five or six squash seeds are planted in a ring 10 or 12 inches outside the beans.
As the beans grow up the corn, you can assist by wrapping the vines around the stalks to make best use of the green trellis. As the squash vines grow, you can pick them up and turn the ends to weave through the stalks to cover the entire soil base. Some of the plants may need to be thinned out so they have enough room to grow and some weeding will still be necessary, but each of these plants should provide ample food to a household desiring to enjoy corn, beans, and squash.
Following the traditional three sisters method works best if you garden in an region with a long growing season. From the time you plant the corn to the time you plant the squash, about a month may have passed. It makes sense to follow the process so you can maintain order and sow each successive seed in its appropriate spot. If planted all at once the beans and squash may overtake and cover the corn before it is tall enough to support itself.
However, if you live in an area with a short growing season, like me, you can still plant the three sisters, but with a few modifications. I don't have an extra month to spare and the delay in planting the squash may mean I won't have a harvest before the first frost in fall.
I plant my sisters all at the same time after the last frost. I lay out a series of mounded rows about two feet apart. I place a corn seed every 10 inches, or so, and plant four bean seeds in a square a few inches away from the corn. I put a squash seed in between each of these groupings. Typically, I'll only plant squash in one row; I don't need to harvest that much squash and the plants in one row are enough to spread out and cover multiple rows.
All of the seeds are planted about one inch deep and all will germinate at about the same time. And, yes, it may be a little confusing when all of the plants sprout from the soil at the same time, but I've never had a problem with them. Corn looks different with its straight shoots, the squash will have broader leaves, and the beans will have little tendrils at their tips. I do have to play an active role in directing the growth of the beans and squash so they don't overwhelm the corn, but it's not a major issue.
By planting the three sisters you make efficient use of your garden space and cut down on some maintenance issues. In the beds where I only grow pole beans, I have to erect a trellis. Where I only grow corn, there are always too many weeds to deal with. Where I only grow squash, much of the soil is wasted as the vines cover it.
Whether you follow the traditional process or opt for a modified version, a three sisters garden deserves a place in your garden. It's efficient, visually stunning, and a great opportunity to teach yourself and others about a farming method that has worked well for centuries.