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Connecticut Garden Journal: Companion Planting

May 31, 2018

Gardening is known for its folklore, especially when it comes to insect controls. Some old wives tales have some truth to them and others, not so much. I’m often asked about companion planting for insect control. Although many say plants such as onions, marigolds, and rue can deter pests, scientifically, few of these folklore remedies have been proven. 

It might happen that you get fewer pests on your tomatoes if onions are growing nearby, for example, but that may be due more to weather. One common companion flower often touted is the marigold. However, modern marigold varieties do not have a pungent repellent scent. Researchers did find that if you grew the French marigold for three months and tilled it under, it will ward off nematodes in the soil.

So, instead of trying to match the right vegetables together or avoid ones that don’t like each other, a better idea is to grow a diversity of plants, including some well-known beneficial insect attractors.

We’ve all heard about planting garlic near roses. But a better herb would be tansy. Ladybugs and lacewings love the yellow tansy flowers and these beneficial insects love the aphids that feed on roses. Planting tansy near potatoes is found to reduce the number of Colorado potato beetles on the plants.

In our garden, I always plant extra fennel, dill, and cilantro. I let some of these plants flower because these herbs are best at attracting beneficial insects. Plus, they look pretty in the garden, too. Strategically plant them in different parts of the garden so beneficial insects will be broadly distributed.

Next week on the Connecticut Garden Journal, I'll be talking about four o'clocks. Until then, I'll be seeing you in the garden.