Companion planting—the practice of pairing plants to enhance their growth—is elemental to the history of agriculture. In the following three vignettes, we will travel across time and space to explore three types of companion planting: symbiotic, sacrificial, and opportunistic.
SYMBIOTIC: Among the most ancient co-planting practices are the Three Sisters. Many North American First Nations have an origin story for why corn, beans, and squash grow in sacred union. The throughline is a story of cooperation, how one individual’s strengths can offset another’s weaknesses. In the excerpt below from Braiding Sweetgrass, Robin Wall Kimmerer describes it beautifully:
Planted in a small hill of soil in May, the seeds of corn, beans, and squash become plants that grow together through the summer and fall into a natural partnership that provides benefits for all three. The corn, bean, and squash plants complement each other in many ways throughout the season.
The corn sprouts from the soil first and is on its way to growing tall when the bean seedling appears and begins its own journey towards the sun. The bean vine climbs the corn stalk without damaging or decreasing the corn’s vitality. At the base of the corn stalk the squash plants grows big and wide, shading the soil and holding moisture in.
The bean plant is a member of the Legume family and has the ability to absorb atmospheric nitrogen and release this nitrogen as nutrients into the soil. This nitrogen provides the corn and squash with much needed natural fertilizer.
Together, the corn, beans, and squash also complement each other in nutritional value. The synthesis of the Three Sisters provides carbohydrates from corn, protein from the beans and vitamins from the squash and is a sustainable selection of healthy foods.
SACRIFICIAL: Among the earliest known texts on companion planting comes from the vineyards of Rome, in the writings of Marcus Terentius Varro, 200 BCE. Varro noted that planting cabbage near grapes proved detrimental to the grapes. Since then, study of the interrelationship between species has led to what is called trap cropping. One plant is, in essence, sacrificed to save another. In the example above, roses and grapes are susceptible to many of the same illnesses and pests. One of the most devastating diseases for a vineyard is powdery mildew. Roses are more attractive to mildew than grapes so vintners watch for it on roses to gauge risk for the vineyard at large.
The manner in which your neighbour keeps the land on the boundary planted is also of importance to your profits. For instance, if he has an oak grove near the boundary, you cannot well plant olives along such a forest; for it is so hostile in its nature that your trees will not only be less productive, but will actually bend so far away as to lean inward toward the ground, as the vine is wont to do when planted near the cabbage. As the oak, so large numbers of large walnut trees close by render the border of the farm sterile.
—Marcus Terentius Varro, 200 BCE
OPPORTUNISTIC: The Douro Valley of Portugal is the oldest demarcated wine-growing region in the world. Romans, then Cistercian monks in the 12th century, terraced the steep hillsides to grow grapes where little else could. An interesting example of companion planting lives on in the Douro. In higher valleys where the land is flatter, the soil deeper, grapes are grown on tall trellises that wind down the hillside in line with the contours of the land. Beneath these trellis conventional crops like corn and wheat are grown. Human ingenuity enabled dual full sun crops to grow in one location. The trellises have the added benefit of suspending the grapes, which is more ergonomic for harvesting.