Just as we understand in the animal kingdom how different, unrelated species will mutually benefit one another, whether intentionally or not, so too does the plant kingdom experience the same caliber of harmony and symbiosis (mutual benefit). Herbs, fruits, grains, vegetables, and ornamental flowers offer a wide variety of benefits to surrounding plants both above soil (pest control, disease, pollination, and physical support) while amending soil nutrition and tilth to deter soil-borne diseases, insects, and weeds, while boosting flavor and yields.
Also known as intercropping among professional growers and greenhouses, companion planting is the purposeful cultivation of mutually beneficial (symbiotic) plants grown immediately next to one another. These companion plants may be similar in size, shape, and taxonomy, or they may be very contrasting and seem to have nothing in common. But it is these differences that make for a healthier, organic, and less labor-intensive gardening season.
History of Companion Planting
For well over a thousand years, various methods of intercropping have been documented throughout the world that are still honored today. Most notably, as Americans, we’re familiar with the Native American agricultural tradition known as the “Three Sisters” method, in which corn, beans, and squash are grown in tandem––corn providing the tall support trellis for beans, while beans replenish the soil with nitrogen, and the low-growing squash cools and protects the roots of both the corn and squash. Chinese rice farmers have intercropped their rice fields with Mosquito Fern (azollo fern) because it keeps other plants from competing with the rice, transfers nitrogen back into the soil, while preventing mosquitoes from laying eggs in the field. Japanese growers traditionally intercrop with clover as a proven weed-suppressant, while East African farmers plant both Silverleaf desmodium and Elephant Grass to deter their seasonal pests. Companion plants are not universal and will need to be adjusted dependent on region, climate, and crop.
One of the most well-known examples of companion planting is the seasonal cultivation of cover crops––legumes and grasses known to replenish the soil of depleted nitrogen. Cover crops, such as clover, fava bean, hairy vetch, and mustards, are generally grown alongside members of the nightshade, cucurbit, and brassica families, to provide nitrogen and nutrients during the growing season. However, many cover crop grains, such as buckwheat, rye, and alfalfa, are planted after the harvest and allowed to overwinter, eventually being turned back into the soil as organic “green manure”.
Despite cover crops being the most well-known of modern companion plants, the most surprising may be traditional culinary herbs. Classic heirloom herbs are one of the best-kept secrets used by growers to deter pests, leafhoppers, and diseases from the garden. Natural oils secreted by aromatic herbs such as catnip, chives, pennyroyal, sage, and rosemary, are known to repel pests due to its, sometimes toxic, chemicals creating an inhospitable environment to many aphids, mites, thrips, and leafhoppers. These same culinary herbs, however, will attract those beneficial insects and pollinators required to keep the garden healthy and productive, while known to improve flavor of surrounding crops such as tomatoes, berries, peas, and root vegetables.
Nearly synonymous with bees, butterflies, and other essential pollinators, wildflowers are truly one of the oldest and most successful companion crops ever. While there are several thousands of known wildflowers in just North America alone, wildflower seed mixes often feature varieties domesticated to specific regions to best attract the local insects and pollinators to the garden.
Despite being traditionally grown for showy aesthetics and simple home decor, common ornamental flowers such as nasturtium, calendula, marigold, petunia, and alyssum––to name a few––are proven garden companions known to deter several disease-carrying pests. Low-growing alyssum, for example, is known to provide protection for spider habitats keeping your garden free of harmful insects while marigolds emit a potent chemical into the soil called limonene which, once established, will repel whiteflies and aphids for multiple growing seasons. Larger-scale farms and home gardens will often plant an entire row of ornamentals and herbs between each row of summer vegetable crops.
Companion planting is not an exact science because there are so many variables when preparing the garden such as climate, region, soil health, and choice of crop to just name a few. If new to companion planting, try a fall cover crop in the garden this season. Whether growing a legume or grain, cover crops are quick to mature and certain to show the fastest return on investment in your future harvests.