JoAnne Skelly: Is companion planting a myth?

Most people have heard of planting certain plants together because they work better as a team than alone.

In the 1970s, Louise Riotte wrote the book “Carrots Love Tomatoes” about companion planting; how one plant may repel insect pests from another plant type, help another to grow or even repel other plants. She suggested that root secretions and odor were important components in the success of planting things together. She wrote that nasturtiums keep broccoli free of aphids and that carrots are good to grow with tomatoes, leaf lettuce, chives, onions and radishes. The onions help keep carrot flies away. Her book is an informal encyclopedia of which plants work together.

Companion planting is a popular concept. I’m a follower of Linda Chalker-Scott, Ph.D, Extension Horticulturist at Washington State University. She is always debunking horticulture myths and advocating scientific literacy. She has written about whether companion planting is a myth.

Her first comment is that the phrase “companion” implies that species like each other. In using that phrase, we are assigning human characteristics to plants. This is not a scientific approach. She then asks, “Is the concept of companion planting a legitimate horticultural practice?”

Chalker-Scott’s article says research has found many benefits in interplanting and maintaining diverse plants associations. These benefits may be “physical, chemical or biological alterations that can improve the establishment and survival of desired plant species.” There can also be benefits from attracting beneficial insects. In addition, researchers are discovering that “many plants share root system connections.” Some plants collect salts in a soil, desalinizing it for salt-sensitive species. Other plants pull toxic heavy metals out of a soil making soils healthy for other plants. Plants in the legume family, such as beans and peas, hold nitrogen in a soil making it available for other plants. Sagebrush provides shade for pinyon seedlings and acts as a nurse crop until the tree establishes. Plants definitely can benefit each other.

Chalker-Scott points out that the problem with the phrase “companion plants” is when science gets lost in the pseudoscience of plant rhythms, vibrations or plant feelings. Most companion plant lists have little basis in fact and are only good for entertainment value. It would be better to use terms such as intercropping or plant associations rather than companions, since those terms are based on science.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu or 887-2252.