Just like humans, plants have friends and foes and can thrive or fail when planted in close proximity to one another. By definition, planting one or more types of plants together in a beneficial relationship is called companion planting. The companion planting method can be used for physical support and protection, repelling pests, and nutrient enhancement that will ultimately increase vegetable yields. 

The companion planting concept is not new, though it was revitalized with the introduction of permaculture in the late 1960s, and again with the organic gardening movement of the 1970s. Companion planting was developed by Indigenous communities and has ancient roots nearly 10,000 years deep. The most documented technique is called “Three Sisters” and was developed by the Haudenosaunee (commonly known as Iroquois) tribes of the Great Lakes, Northeast, and Canada. 

The three sisters are maize (corn), squash, and climbing (pole) beans. Planted in harmony, the three sisters each play a role. The squash serves as a weed suppressor and shield from the sun, the beans replace nitrogen in the soil, and the corn stands as a strong structure on which the beans can grow. 

Interplanting with complementary plants can help ensure crops are not competing for nutrients and resources. Crop monoculture--one-crop farming methods--can lead to a variety of problems for plants and the environment alike. In a diverse planting environment, plants that have evolved to coexist make use of different available nutrients in the soil, and don’t deplete any one nutrient. This scenario enhances the health of the soil. When only one type of crop is grown it depletes the soil of the specific nutrients needed for that crop to grow.

Eventually the soil becomes damaged and synthetic fertilizers are required for the soil to keep producing. Overuse of synthetic fertilizers can push the natural ecosystem of the soil out of balance permanently. Companion planting and crop rotation is recommended in order to balance the nutrients available in the soil of your backyard garden. 

Companion plants can provide support or protection from the environmental elements of the garden. For example, taller plants like pole beans and corn can provide a wind shelter and sun protection to plants like lettuce. Sunflowers give vining plants like beans a secure structure to climb. Ground spreading plants like squash and melon provide sun protection and weed suppressant for other above ground plants, and carrots break up the soil for tomato plants to build strong root structures below. 

Many herbs and flowers can be used to deter pests, eliminating the need for harsh chemicals in the garden. Planting a liberal amount of basil will help deter hornworms, one of tomatoes’ biggest pests. The roots of a marigold repels nematodes in the soil. 

The smell of the marigold flower discourages four legged creatures, like rabbits, from nibbling on the crops as well as cabbage moths and bean beetles, all of which can quickly decimate a bean crop. Nasturtiums are a good companion plant for brassicas (cabbage, broccoli) because they deter cabbage oopers and attract beneficial insects and are great beneficial insect shelters when intertwined with cucumbers. Dill can also attract beneficial insects, like wasps, that keep the cabbage looper population controlled. The sticky stalks and flower undersides of calendula are effective aphid traps. These flowers work best when used circumferentially with cole crops like kale, collards, broccoli, and cabbage, but can be planted anywhere in the garden to attract pollinators. 

In contrast, some plants are incompatible and interplanting should be avoided. Plants in the allium family, like onions and garlic can stunt the growth of beans and peas. Growing potatoes near tomatoes, cucumber, squash, and pumpkins make them more susceptible to dreaded blight. Carrots should not be grown near dill because of cross-pollination issues. 

When planning a garden, knowledge of companion planting can go a long way toward happier, healthier vegetables. Be sure to consider the growing patterns and watering needs of each plant to maximize production and yield. The chart is a basic guide for some of the most popular backyard vegetables and herbs, there are many more companion plants and theories of interplanting out there.