Companion Planting Myths and Facts

Just when I thought I couldn’t find another more controversial gardening topic to write about, I stumbled into a whole hornet’s nest of controversy surrounding companion planting. Now for my black thumb friends out there – my lovely readers who are brand new to gardening – you may be scratching your head and wondering just what the heck companion planting is all about. Others are leaping from their computer in horror, making the sign of the cross and shouting, “No! No! Companion planting, a myth? But what about the great book Carrots Love Tomatoes?” and so on and so forth.

The issue surrounding companion planting isn’t the basic premise behind the idea that some plants grow well together, it’s the pseudo-science surrounding the concept of companion planting. Let’s take companion planting one step at a time before diving into the controversy.

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 What Is Companion Planting?

Companion planting is the idea that one type of plant benefits from being planted near another. The notion behind this gardening technique is that some plants exude chemicals naturally that repel insects, nourish the soil, or somehow “help” another species of plant.

Take tomatoes and marigolds, one of my favorite combinations because it actually works. Marigolds offer a strongly scented chemical compound that naturally repels tomato hornworms. It works, it’s safe, and it’s a companion plant that looks pretty.

Does It Work?

It does – to some degree. Where the experts disagree with the folklore is in the actual effect and pairing of the plants.

Certain plants, as in my marigold example, do seem to work to repel insects. There’s also a concept in organic gardening parlance called trap crops, where plants are used like lures or traps to entice bugs to visit the sacrifice plant and leave the ones you want to grow alone. Like planting marigolds around tomatoes, these methods do work to some degree.

Don’t Fall for Hype

The problem with many articles and books discussing this topic is that they take the concept into quasi-scientific levels. Plants do influence the soil around them, and they do influence surrounding plants. Plant a walnut tree and then try to plant flowers underneath; it quickly becomes apparent that “something” is at work that prevents flowers from growing under a walnut tree. That “something” is a known, measurable chemical exuded by walnuts that makes the soil unappealing and untenable for a wide range of plants. Again, in this example, there’s a measurable scientific explanation for why walnuts have this effect, just as the chemicals in marigold leaves and flowers can be measured.

Folklore Planting Schemes

Many gardeners rely upon folklore for planting schemes, and that’s where the experts at the Cooperative Extension and the university systems strongly disagree. Although nothing harmful will come from planning your garden according to moon phases, planting by crystals, and all sorts of folkloric traditions, nothing beneficial will happen, either.

The Science Behind Combinining Certain Plants

I took a few minutes to discover some good scientific studies behind companion plants.

As for me, I’ll stick with pairing my basil and marigolds with tomatoes and trying to grow lettuce under the soft shade of tomato vines.

 

• Companion Planting in the Vegetable Garden, U Mass Center for Agriculture