Companion planting is the practice of growing one plant to assist a different plant as part of a community of plants. Fruits, vegetables, and herbs can be more productive and resilient when each plant supports a different plant or plants.
Benefits of companion planting include pollination, pest control, physical support or trellising, and even weed control. Sometimes the benefits are one-way from one plant to another, and other times the benefits are reciprocal, such as when the famous Three Sisters of corn, pole beans, and squash or pumpkins are grown together for mutual benefit.
Indigenous peoples—including the Seneca, an Iroquoian tribe inhabiting western New York—cultivated the Three Sisters (Diohe’ko) for hundreds of years. Work parties of Iroquois women planted, cultivated, and harvested the Three Sisters crops.
Meals resulting from a Three Sisters planting—corn and squash for energy and beans for proteins—were an important part of a nutritious diet for Indigenous peoples. The Three Sisters were not just an important agricultural system; they were an important part of the culture of the Iroquois, as the Three Sisters were protagonists in a number of Seneca tales, myths, ceremonies, and legends.
How does each “sister” benefit the others?
Nitrogen-fixing legumes, like beans, are able to have a relationship with rhizobium, a bacteria in soil, which benefits both bacteria and beans. These bacteria form nodules on the bean sisters’ roots.
They are then able to take in atmospheric nitrogen, usually unavailable to plants and convert it to a form which plants can use. This is good for the bacteria, the bean, squash and, especially, corn!
Corn requires a lot of nitrogen to grow well and benefits greatly from nitrogen-fixing beans.
What does the corn Sister contribute?
Pole beans are able to climb the corn stalks. Also, the high canopy of corn foliage may confuse the adult squash borer and reduce the damage of this pest on the squash.
Finally, the broad-spreading leaves on the vines of the squash sister provide living mulch for the corn and beans to reduce weeds and conserve soil moisture. Also, prickly squash vines climbing corn stalks may deter raccoons from feeding on the corn.
Other benefits of companion planting
There are several other important ways that companion plants help each other as a result of their close proximity. Trap cropping is the practice of planting something near a crop which you wish to protect from a specific pest.
The trap crop is planted to lure known pests away from the crop you wish to protect from that pest. An example is planting dill among tomatoes. Tomato horn worms prefer the dill, and once you notice the foliage of the dill being devoured by the voracious horn worms, you can remove the pests before they move on to the tomatoes.
Nasturtiums planted among vegetable crops will attract aphids and many other pests, providing protection for nearby brassica crops such as broccoli, cabbage, collards, and kale. Planting a trap crop of blue-hubbard winter squash can be an effective method to lure cucumber beetles away from other varieties of squashes and cucumbers.
Most gardeners would gladly sacrifice blue-hubbard squash to protect their prized zucchinis and yellow crooknecks!
Marigolds planted among vegetable-garden rows can benefit their edible neighbors through biochemical pest suppression. Marigolds produce thiophene, which deters harmful nematodes in the soil.
Providing shade and a cooler microclimate for certain plants can also be accomplished with companion planting. Try extending the harvest season of cool-season crops, such as lettuces and greens, by planting a taller crop with an upright growth pattern to provide shade and conserve soil moisture in the heat of early summer.
Parsley, borage, scarlet sage, and even yarrow or coneflowers can provide protection from the hot afternoon sun.
Many companion plants provide attractive environments for beneficial insects, such as pollinators, and predator species, such as lady beetles and lacewings, that help reduce populations of many different harmful pests.
Plants in the Umbel family (carrots, parsley, and dill) are known for this, as is sweet alyssum.Using trap crops when companion planting in order to lure insects away from certain crops is preferred over the routine use of synthetic insecticides, as most insecticides do not distinguish between good bugs and bad bugs and kill the beneficial insects along with the harmful ones.
Mike Hogan is Extension Educator, Agriculture and Natural Resources and associate professor with Ohio State University Extension.
