JoAnne Skelly
When I have a question about the validity of a horticultural practice, I check out what Linda Chalker-Scott, horticulture professor with Washington State University, has to say on the topic.
When wondering if companion planting was legitimate science, I read her article: “The Myth of Companion Plantings” at https://s3.wp.wsu.edu/uploads/sites/403/2015/03/companion-plantings.pdf. Putting plant companions together supposedly benefits each of them. Do carrots really love tomatoes? Does planting corn, beans and squash together, the “Three Sisters” method of native planting, have a basis in science?
In the case of the “Three Sisters” beans definitely fix nitrogen into the soil benefitting themselves and plants around them. Corn stalks provide support to the beans. Squash leaves shade the soil, reducing evaporation and inhibiting weeds.
These three plants have the same environmental requirements and work well together. Perhaps instead of applying a term that has often been used in pseudoscience, a better way of describing this is to call it intercropping or polyculture writes Chalker-Scott.
Diverse plant associations can be beneficial according to research, particularly in attracting and retaining beneficial insects, which can reduce pest pressure on plants. The same is true about the mycorrhizal relationships between roots of various plants. Mycorrhizae (symbiotic fungi) help with nutrient transfer.
Chalker-Scott points out another positive interaction in that some plants in arid environments pull salts out of the soil, which benefits less salt tolerant species. Other plants isolate heavy metals to the benefit of other plants.
Another beneficial relationship is with nurse plants, such as pinyon pines growing in the shade and protection of sagebrush plants. “There is no scientific basis, however, for any of the several lists that exist describing ‘traditional companion plants,’” according to Chalker-Scott. The term is too broad and misleading.
Research does support that there are “physical, chemical and biological” interactions and changes that can benefit plants. Intercropping short season crops with later maturing ones can save space in the garden.
Different root structures may help aerate the soil breaking up heavy soils and may access nutrients at different soil levels. Legumes (beans, peas and clover) do fix nitrogen in the soil, improving nutrient availability for plants grown with them.
Some plants, such as sunflowers, act as pest traps, luring pests, such as aphids, away from desirable plants. Others, such as dill, attract pollinators. There are definitely benefits in planting our gardens in a more holistic way according to Nations and Mah, University of California Master Gardeners.
They suggest we see them as ecosystems of biodiversity. Nations, C. and M. Mah, June 16, 2022. “Better together: the new science of “Companion Planting.” https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=53468.
JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.