History
In China the mosquito fern (Azolla species) has been used for at least one thousand years, as a companion plant for rice crops. It hosts a special cyanobacterium that fixes nitrogen from the atmosphere, and also blocks out light from getting to any competing plants, aside from the rice, which is planted when tall enough to stick out of the water above the azolla layer.
Companion planting was practiced in various forms by the indigenous peoples of the Americas prior to the arrival of Europeans. One common system was the planting of corn (maize) and pole beans together. The cornstalk would serve as a trellis for the beans to climb, while the beans would fix nitrogen which also benefited the corn. The inclusion of squash with these two plants completes the Three Sisters technique, pioneered by Native American peoples. In the southwest, sunflowers were also grown along with beans as a trellis for them, or just to the north of the Three Sisters, to draw away aphids.
Companion planting was widely promoted in the 1970s as part of the organic gardening movement. It was encouraged for pragmatic reasons, such as natural trellising, but mainly with the idea that different species of plant may thrive more when close together. It is also a technique frequently used in permaculture, together with mulching, polyculture, and changing of crops.
Read more about this topic: Companion Planting
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