Squash, beans, and corn have a long history of being planted together to benefit each other, the soil, and the nutritional needs of the people who grew them.

nan fischer
Dec 18, 2018 · 6 min read
Celebration winter squash — photo ©nan fischer

Before humans began practicing agriculture about 12,000 years ago, beans, squash, and teosinte grew together in the wild near Oaxaca, Mexico. As indigenous people transitioned from a hunter-gatherer culture to an agricultural one — during a span of about 5,000 years — they slowly abandoned their nomadic lifestyle and domesticated these wild plants for a more stable food supply.

Squash (Cucurbita spp.) was the first of the trio to be domesticated, about 10,000 years ago. It was originally grown for its hard rind — which was used for bowls and utensils — and then for its nutritious seeds. The flesh was bitter, but indigenous people eventually bred squash for better flavor and texture.

Teosinte is the likely wild progenitor of maize (Zea mays). About 9,000 years ago, the Mayan people turned this grass — with its impenetrable 12-kernel seed head — into an edible and adaptable crop. Since then, maize has been bred into dozens of varieties with more genetic diversity than many other plants.

The common bean (Phaseolus vulgaris) is native to Mesoamerica and the Peruvian Andes. Originally a vine with twisted seedpods and small seeds, it’s been selected and bred for larger seeds and bush growth for nearly 7,000 years.

Ancient Agriculture: The Milpa

Mesoamerican farmers imitated nature by growing crops together in a milpa, which was a field of maize, beans, squash, avocados, jicama, and other wild plants that they’d tamed. Milpas were traditionally farmed for a few years and then allowed to go fallow for better production. The symbiotic relationships among the plants in the milpa created a healthy and richly diverse ecosystem. The plants supported one another, offered habitat for wildlife, and complemented each other nutritionally, providing a balanced diet. In his book 1491, Charles Mann states that milpas have been continuously planted for about 4,000 years.

Through extensive trade routes, this farming system spread across Mexico. Gradually, the milpa made its way to the pueblos of the Southwest, extended farther north to the Great Lakes region, and migrated finally to northeast North America. Some of the tropical plants of Mexico’s milpas weren’t adaptable to the colder regions, but maize, beans, and squash were successfully bred for the shorter growing season and vital winter storage.

Although most native people grew maize, beans, and squash together, the Iroquois named the system Three Sisters or Deohako. Each nation had its own legend about these plants, the common thread being that the sisters were very close and stronger together than they were apart, which helped the people survive.

In the field, towering maize stalks provided support for vining beans, which helped tie the stalks together for added stability. Beans also pulled nitrogen from the air and, through decomposition, transferred it to the soil, making it available later to the maize and squash, both of which are heavy nitrogen users. The broad, low-lying squash plants acted as mulch to suppress weeds, conserve moisture, and keep the soil cool. Plus, their prickly stems deterred predators.

A milpa of maize, beans, and squash Zaragoza, Tilantongo, Oaxaca, wikimedia

Nutrition for the Earth and the Farmers

The biological diversity of maize, beans, and squash grown together creates a polyculture. Each plant utilizes different nutrients in the soil and then returns those nutrients to the soil as they decompose. The root systems of these three crops are of varying sizes and depths, which helps to break up the soil, and because each crop is a different height, they’re each able to capture available light from various angles. Diversity provides protection from devastation, too. One pest or disease wouldn’t wipe out an entire field, and a harvest of some sort is nearly guaranteed.

Maize, beans, and squash also complement one another for a nutritious and well-balanced diet. For example, the combination of maize and beans creates a complete protein. Squash is full of vitamins and minerals that the maize and beans both lack, and squash seeds provide oil and protein. Maize and squash are also both high in calories, which help sustain energy.

The benefits of growing these three crops together are clear to modern soil scientists and nutritionists, although at the time there was no scientific knowledge behind this sophisticated planting method. It was simply the result of Mesoamerican farmers being keenly aware of their environment and experimenting for thousands of years to grow the hardiest and most nutritious crops.

Growing the Three Sisters

Eastern and northern nations grew the Three Sisters in rows of mounds about 4 feet apart on center. In regions with regular rainfall and cool springs, the mounds were warm, dry microclimates in the field. In some locales, the maize and beans were planted in the mounds, and the squash grew between the rows. Where fish was abundant, carcasses were placed in the mounds as fertilizer. At the end of the growing season, the finished plant remnants were incorporated directly into the soil for added fertility.

The Tarahumara of northwestern Mexico, on the other hand, planted a block of several rows of corn and surrounded it with beans. They planted squash along one side of the field.

In the arid Southwest, the Three Sisters weren’t always planted side by side, either. According to the nonprofit Native Seeds/SEARCH, the Hopi and Navajo planted each crop in a separate part of the field and used wide spacing to take advantage of scant rainfall. Farmers in this region sometimes grew sunflowers and amaranth, which were also important food sources, along with the Three Sisters. The Hopi grew wild cleome (Cleome serrulata, or Rocky Mountain bee plant) to attract pollinators for the squash.

Bean plants, photo ©nan fischer

Post-European Contact

After Columbus’ arrival, colonizers took some native seeds across the Atlantic Ocean to Europe. There, maize, beans, and squash were bred and developed separately, along with many other foods. European settlers returned to North America with new cultivars that had developed characteristics suitable to their European environments and were labeled with European names.

As Europeans moved west, these crops spread west, too, and some have become today’s heirlooms. Others — the most economically important — have been hybridized and engineered for almost 100 years, making the seeds impossible to save true to form and resulting in an increased loss of seed diversity. And yet, some of the original, or purely Native American, cultivars remain, thanks to the efforts of the strong cultures that continue to nurture them and others who have recognized the importance of these cultivars over the centuries.

Continuing the Ancient Tradition

The milpa was the first deliberate companion planting system in the Western Hemisphere, and maize, beans, and squash were the hardiest and most adaptable of those crops for northern climates. Like all of our food, though, they first grew in the wild thousands of years ago.

Today, with the rising popularity of organic gardening and an increasing awareness of indigenous agricultural history, the Three Sisters system is returning to backyard gardens. A handful of native seed cultivars are available commercially, but the best seed choices are those grown locally because they’ve adapted to the soils and weather of the region. To keep the Three Sisters tradition going, and to honor the ancient farmers of Mesoamerica, try growing heirloom squash, beans, and maize together, and save seeds from the hardiest, tastiest, and most beautiful open-pollinated plants in your garden.


nannie appleseed

A place to compile years’ worth of my gardening articles and photos, and recount the 2019 growing season as it unfolds.

nan fischer

Written by

Writer, thinker, reader, picture taker. Gardener, dog lover, earth mama. Unmistakeable introvert. https://twitter.com/nan_fischer

nannie appleseed

A place to compile years’ worth of my gardening articles and photos, and recount the 2019 growing season as it unfolds.

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