Companion planting: Combining plants for a healthy, well-balanced garden

JACKSONVILLE, Ill. — As we creep toward spring, many gardeners begin to get the urge to get out in the garden. Seed starting and garden planning activities are well underway. One gardening technique that many gardeners incorporate into their gardens is companion planting.

What is companion planting?

There isn’t an agreed-upon definition of what companion planting is. Generally speaking, companion planting is planting at least two different types of plants together that will benefit at least one of them.

Another way to think of companion planting is intercropping, growing two or more crops together, or polyculture, which includes the crops being grown and non-crop plants. Essentially, trying to increase diversity to create a healthy, well-balanced garden.

Some potential benefits of companion planting

There are a variety of different ways in which plants can potentially benefit, including improving the soil and pollination and reducing pest and weed pressure. So, how can companion planting be incorporated into our gardens?

Improving soil. While some may not consider them companion plants, cover crops are a great way to help improve soils, benefiting the crops following them. Cover crops can help reduce soil erosion, add organic matter, improve soil structure and increase soil fertility.

Reducing weeds. In addition to improving soil, cover crops can also be used to suppress weeds. Cover crops like winter/cereal rye can be used as mulch after they have been terminated. Cover crops can also be used as a living mulch to provide continuous ground cover to help suppress weeds. For example, white clover can be grown on walking paths to keep weeds down. The living mulch will need to be maintained to prevent it from becoming a weed itself.

Managing pests. Trap cropping can be used, where a ‘sacrificial’ companion plant is planted. These trap crops should be planted before the crop you’re trying to protect (main crop). Pests will be attracted to them and can be killed or disposed of. One example is using blue Hubbard squash, which is highly attractive to squash bugs and vine borer, to protect other pumpkin and squash cultivars.

Support beneficial insects. Many vegetable crops rely on pollination to produce fruit, while others may have increased production and quality if they are visited by pollinators. Incorporating flowering plants into vegetable gardens can help attract pollinators and improve pollination. Flowers can also attract natural enemies that can help manage pest populations.

The Three Sisters

Probably the best-known companion planting practice is the Three Sisters, which utilizes corn, beans and squash. In this system, the corn supports the vining bean plants. The beans act as a nitrogen-fixing crop, and the squash plants act as a living mulch that suppresses weed growth and helps maintain soil moisture.

Some caveats to companion planting

Unfortunately, there hasn’t been a lot of research done, especially on a garden scale, on companion planting. Many recommendations are based on questionable methods (sensitive crystallization) and anecdotal evidence. Others are based on large studies or lab results that may (or may not) apply to a garden setting.

The interactions between plants and their environment are complex, making it difficult to determine if growing particular plants together is beneficial. This is perhaps best explained by Dr. Michael Bomford: “Garden-scale intercropping [companion planting] can offer advantages over monoculture, but these are not achieved simply by combining certain compatible companion species. Crop density, ratio and relative planting times all affect the way that companion species interact with one another and their environment.”