Companion Planting: Myth or Truth?

You’ve likely heard of companion planting, but do the principles work?

Sometimes yes, sometimes no; and other times maybe.

Companion planting is the practice of growing certain plants together or in near proximity for a mutual benefit, such as enhancing nutrients, pollination, and crop yield. Some successful companion planting principles have been passed down through generations, and some have been scientifically studied and proven. Others, however, lack any scientific proof that they work.

Companion planting can help gardeners maximize their gardening space, improve soil health, and manage weeds and insects. Be mindful of the information you find online -- it may or may not be backed by scientific data. That means a particular companion planting may or may not be effective in your garden.

Some companion planting principles that work

• Planting early-season crops and late-season crops in the same bed can help tame weeds by providing cover for the soil throughout the growing season.
• Planting legumes as a cover crop or underneath another crop can help reduce fertilizer needs.
• Using flowers or herbs to help deter or attract harmful and beneficial insects. Planting a variety of plants with different heights, leaf shapes, and colors can confuse some insects.

In some instances, the benefits are blurry. Marigolds are often planted in or near vegetable gardens to deter insects, but they may not provide the kind of protection for which some gardeners give them credit.

One study did find that biochemicals produced by African and French marigolds can kill nematodes that feed on plant roots, but only after the spent plants have been tilled into the soil. A few other studies showed basil and marigolds together reduced thrip populations in greenhouse-grown and field-grown tomatoes. Another study showed marigold, nasturtium, and onion helped reduce populations of cabbage looper and imported cabbageworm in cabbage.

No matter what, companion planting can provide diversity to the landscape -- a benefit that is welcome in any type of garden.

For more on companion planting, check out these resources from our Extension friends at the University of Massachusetts Amherst Center for Agriculture, Food and the Environment and University of Minnesota Extension.