A New Look At Companion Planting

Tomatoes love carrots. Sounds like a grade-school romance. Tomatoes and carrots, Marigolds and salad greens. Plant pairing has been around for a long time. Its history is filled with folklore passed from one generation to the next. Only recently has it been backed with scientific research. So keep reading for companion planting that really works and how!

Why practice companion planting?
As we become more aware of the importance of attracting pollinators to our yards, it makes sense to take the next step of creating a yard full of biodiversity - including in the vegetable garden. More diversity of plant species leads to a greater diversity of insects. Those insects feed on other insects that are wreaking havoc in our gardens. When this ecosystem is in balance, we gardeners can step back and let nature do its thing. We’ll have healthier plants, and use fewer pesticides.  

Debunking a myth
Let’s begin with the marigold myth. A common practice is to plant marigolds around the vegetable garden to repel pests and rabbits. Research has shown that marigold’s strong odor does mask the smell of certain host plants and does keep insects at bay, but to a very specific pest. Planting marigolds with members of the onion family will deter onion root maggot flies. Marigolds are also effective when planted with broccoli and other brassicas to deter cabbage root maggot flies. And, by the way, marigolds do not repel rabbits. I’ve seen rabbits munching away on them. 

Science-proven examples
Tomatoes actually love radishes. Young tomato seedlings can be susceptible to flea beetles, but the beetles prefer radish leaves, so interplanting radishes with tomatoes is an effective trap-crop technique. Tomatoes also love basil. When tall varieties of basil are planted around tomatoes, research has shown that it reduces the number of eggs laid by the five-spotted hawk moth that mature into tomato hornworms. Here are more examples:
    

• Partner dill with cole crops to reduce egg-laying of the cabbage worm. 

 

• Interplant lettuce with Sweet Alyssum to enhance the biological control of aphids that attack lettuce crops. Sweet Alyssum attracts parasitic wasps that prey on aphids.

 

• Interplant nasturtiums with zucchini and other squash varieties to deter squash bugs.

Create a haven for beneficial insects
Most good bugs need more than protein sourced from their prey to survive. They also need pollen and sugary nectar to reproduce. Let’s go back to the tomato hornworm. It has a natural predator - the larvae form of a parasitic wasp. The adult parasitic wasp lays its eggs under the skin of the hornworm. When the eggs hatch, the larvae feed on the hornworm, eating their way out. The adult form - the parasitic wasp - requires sugars found in flower nectar. This is also true of ladybugs and lacewings and many more beneficial insects. We can create an environment for these beneficials in two ways: by planting specific nectar plants for specific beneficials, and by including a large diversity of flowers to attract and sustain a broad spectrum of beneficials. 

As you plant your vegetable garden this spring, consider using a few of these simple techniques to grow healthier plants in a natural way. Get yourself a good book to learn more about it. I recommend Plant Partners by Jessica Walliser. You can also explore this topic further by joining me for a free monthly virtual gardening discussion on Wednesday, May 11 at 6:30 pm. Register here.