Plants benefit each other in a number of ways. These relationships can enhance the health of garden crops, provide support or shade and attract or deter pests.
For example, corn and beans in a “Three Sisters” garden serve as natural trellises for the smaller beans and squash while adding nitrogen to the soil. The dappled shade from the taller corn plants also helps suppress weeds and keep the ground cool.
Attracts Beneficial Insects
The first thing that comes to mind when people think of companion planting is insect pest control. Many plants naturally repel insects or trap them, and when planted near vegetables, help to prevent pests from damaging the crop.
Strongly scented plants like marigolds Calendula officinalis, garlic chives Allium tuberosum and lavender Lavandula angustifolia confuse and deter insects searching for their own food by scent, thus helping to reduce garden pests. Another popular option is tansy Tanacetum vulgare which repels aphids, cabbage maggots, carrot rust mites, cutworms and earwigs. It also attracts hoverflies and braconid wasps that prey on aphids.
Plants with complementary nutrient requirements can be planted together to enhance growth and improve soil fertility. For example, legumes like beans and peas release nitrogen-fixing bacteria into the soil that enriches it. When planted alongside nitrogen-hungry crops like tomatoes and lettuce, they enhance the plants’ ability to absorb this nutrient. Similarly, planting cool season crops like lettuce and spinach in between larger, faster-growing crops such as tomatoes and peppers conserves space and allows the slower growing vegetable to offer shade.
Prevents Weeds
Traditionally, companion planting deters pests and improves garden health and yield by interplanting crops that complement each other. The classic example of this is the Three Sisters method used by Native American cultures: corn, beans and squash are grown together for mutual benefit. Corn provides a natural support trellis for climbing beans and squash, while beans boost soil nutrients with their nitrogen-fixing abilities and squash leaves help shade the ground to conserve moisture and inhibit weed growth.
While science hasn’t validated some of the traditional companion plant suggestions (roses love garlic), there is growing evidence that certain combinations are beneficial. For example, planting wormwood alongside cabbage family vegetables deters cabbage moths, and marigolds inhibit Mexican bean beetles. In addition, planting basil near tomatoes attracts ladybugs that naturally control aphid infestations. This allows you to avoid the use of chemical pesticides in your vegetable garden. Then you can enjoy fresh, nutritious homegrown food without the added chemicals.
Attracts Pollinators
When vegetables are planted with companion plants that attract beneficial insects, the insects quell pest populations and help produce larger crops.
For example, nasturtiums are a natural enemy of tomato hornworm and help repel this damaging pest. Other flowering plants like marigolds, zinnias, basil and borage are also good insect allies. The fragrant herbs dill, rosemary and thyme also deter many common vegetable garden pests.
Companion planting can also physically support or “stack” crops to save space in the garden and improve soil health. The three sisters model of corn, beans and squash is a classic example; corn provides a climbing frame for the beans, and the beans suppress weeds and deter nematodes while providing shade to the corn.
The best thing to remember when it comes to companion planting is to experiment and see what works for you! The more diverse your crop combinations are, the better. And don’t forget that crop rotation is important to reduce the buildup of disease and pests in the soil over time.
Attracts Beneficial Birds
Plants that attract pollinators, deter pests and act as natural pest repellents can help reduce the need for chemical pesticides in your garden. This is especially important if you use organic methods of gardening like container gardening, backyard gardens and raised beds.
For example, planting basil near tomatoes will attract lady bugs which are natural predators of aphids and can help balance out aphid problems. Other herbs like chives and parsley repel mosquitoes, while attracting hover flies (which eat aphids).
Long time gardeners and farmers have been using companion planting for years. Although some scientists have been hesitant to support the practice, more research is showing that it provides benefits including biological pest control, protection, support and the sharing of soil nutrients. It also offers opportunities to maximize space and the efficiency of a home or garden vegetable garden. Darwin was down with diversity and so should you be!