The following is an excerpt from Gaia’s Garden: A Guide to Home-Scale Permaculture, Second Edition  by Toby Hemenway . It has been adapted for the Web.
Nature binds plants into interdependent communities and associations. Indigenous people, too, have crafted plant combinations that weave synergies among species. In the past two decades, ecological designers also have blended plants into communities that contain partnerships. Permaculturists call these imitations of natural associations guilds.* Formally defined, a guild is a group of plants and animals harmoniously interwoven into a pattern of mutual support, often centered around one major species, that benefits humans while creating habitat.
Guilds are one way to bridge the broad gap between conventional vegetable gardens and wildlife gardens by creating plant communities that act and feel like natural landscapes but that include humans in their webwork. Vegetable gardens benefit only humans, while wildlife or natural gardens specifically exclude people from their ecological patterns.
Gardens for wildlife are immensely valuable, but they are only a partial answer to habitat loss. As I’ve said before, if we ignore the material needs of humans in our urban and suburban landscapes, we’re doomed to continue our voracious consumption of wild land for factory farms and tree plantations. Ecological gardens, using guilds and the other tools described in this book, help our developed land to blossom into nourishing places for both humans and wildlife.
The Three Sisters
Let’s begin our exploration of guilds with a very simple example that illustrates some essential principles. Then we can proceed to more complex guilds—ones that go beyond vegetables.
Familiar to many gardeners is the Native American triad of corn, beans, and squash, a combination often called the Three Sisters. The trio qualifies as a guild because each of these plants supports and benefits the others. The beans draw nitrogen from the air and, via symbiotic bacteria, convert the nitrogen to plant-available form, boosting the growth of all three vegetables. The cornstalks form a trellis for the bean vines to climb. The rambling squash, with its broad leaves, forms a living parasol that densely covers the ground, inhibiting weeds and keeping the soil cool and moist. Further cementing this trio together comes the news from scientists that the roots of the corn ooze specific sugars that are the perfect nourishment for the nitrogen-fixing bacteria.
Together, the Three Sisters produce more food, with less water and fertilizer, than a similar area planted to any one of these three crops in isolation. Jane Mt. Pleasant, an agronomist at Cornell University who has blended her Iroquois heritage with her research, has shown that total yields of this guild, measured in calories, are about 20 percent higher than comparable yields of corn grown alone in an equal-sized plot.
Look at how many interconnections this guild bears. Beans furnish nitrogenous fertility for themselves, the corn, and the squash; squash shades soil for the benefit of all three; corn feeds the bean-hugging bacterial nodules and creates a trellis for the beans. Three plants, weaving at least eight connections. The Three Sisters guild is a perfect place to begin creating a richly connected garden.
Growing the Three Sisters Guild
Mark out a series of planting mounds about three feet apart, a couple of inches high, and a foot or so in diameter. (To calculate how many mounds you need, figure that you’ll get about four or five ears of corn per hole.) Then poke three or four kernels of corn into each mound. Your favorite sweet corn variety will do, although Native Americans developed shorter, multi-stalked cultivars specifically for this guild, such as Black Aztec, Hopi White, or Tarahumara sweet corn, so you might consider a similar many-stalked variety. When the corn sprouts, start mounding the soil up around the young stalks. Don’t cover the sprouts; just build up earth around the base. These mounds, by exposing soil to the air and sun, will warm the sprouts, speeding their growth. The mounds also improve drainage. Don’t thin the corn—you want two or three stalks per mound, hence the greater-than-usual distance between mounds.
About two weeks after planting the corn, select some pole beans, rather than a bush variety. Common pole bean varieties such as Blue Lake work well enough, although I’ve been told that very vigorous hybrid pole beans clambering up skinny hybrid corn stalks can pull the spindly corn down. Again, old-style varieties used traditionally in the Three Sisters work best. These include less-vigorous climbers such as Four Corners Gold and Hopi Light Yellow. But plants are forgiving, and most varieties will do well enough.
If you can, coat the bean seeds with a legume inoculant specific for beans (available from many seed suppliers). This ensures that the all-important nitrogen-fixing bacteria will find a happy home among the bean roots. Plant two or three bean seeds near the edges of each corn mound.
At the same time you start the beans, plant squash or pumpkins between each mound. Don’t use zucchini, as their tall stems will push the corn aside. Grow a vining squash variety that will sprawl over the soil.
Aside from these trio-specific instructions, grow the Three Sisters by following the cultural guidelines on each vegetable’s seed packet. After harvest, leave the stalks, vines, and other organic debris on the ground to compost in place. This returns some of the extracted fertility to the soil and protects the ground from erosion. Although much of the bacterially fixed nitrogen will be concentrated into the protein-rich bean pods, plenty will remain in the vines and roots, ready to go back to the earth.
* The term guild is used by ecologists to mean something slightly different (a set of different species that use a common resource in a similar way, as in “the guild of seed-eating birds”). This overlap is unfortunate and potentially confusing, but permaculture’s use of the term guild is well established, and I will stick with this common usage rather than introduce another term.