Companion Planting for Pest Control

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Companion planting is a popular topic for beginning gardeners. Though the idea of situating plants next to each other can have various benefits, I think most gardeners want to know more than what plants grow well together. I think instead, we’re thinking far more practically.

What can I plant in my garden to keep pests away?

Doesn’t every organic gardener want to know this? We don’t want to use pesticides, so we want to know what herbs deter pests, what flowers deter caterpillars, and what plants repel specific insects that plague our gardens.

While scientific research on the topic of companion planting for pest management is still in its infancy, blog posts, books, and articles abound with ideas. But what suggestions are based in science and which ones are based in old wives’ tales? 

In today’s episode of the Beginner’s Garden Podcast, I share 4 principles for using companion planting for organic pest control. Click below to listen to the full discussion, or read the article below:

 

4 Principles for Using Companion Planting in Organic Pest Control

Principle 1: More Plant Diversity Equals Fewer Pests

Though there will always be skeptics, pretty much everyone agrees that the more diversity you have in the garden the fewer pests you will deal with. Include flowers and herbs with your vegetables. By doing this, you create a habitat for good insects and confuse the bad ones. The scents of certain herbs and flowers can interfere with a pest insect finding its preferred host plant.

marigold in companion planting

Why is Companion Planting Important?

Because companion planting nurtures a balanced environment and keeps many invasive pest populations in check, we can avoid chemical pest control. Large scale agricultural plots with no diversity rely heavily on chemicals for pest control. If we can plant different crops near each other, we can help prevent pests naturally.

Principle 2: Grow Companion Plants that Create a Habitat for Beneficial Insects

What Herbs Deter Pests?

Whenever I have read about companion planning with herbs, these have always been mentioned: mint, tansy, catnip, wormwood, dill, basic, parsley, fennel, and cilantro. Herbs like mints and tansy tend to be invasive so avoid planting them directly in the garden. Instead, put them planted in a pot near your vegetables.

dill flowers attract beneficial insects
dill flowers attract beneficial insects

What Flowers are Best for Pest Control?

The queen of flowers to use for pest control is nasturtium. It is thought not only to deter pests but also act as a “trap crop” for pests who prefer its taste over your prized vegetables.

Marigold attracts beneficial insects as well as protects against the root knot nematode. It may be even more beneficial as a cover crop.

Cosmos and alyssum attract all kinds of beneficial insects including bumble bees and syrphid flies.

companion planting cosmos flower to attract beneficial insects

Let Vegetables Flower

We all hate it when our onions bolt because it means the bulb is no longer growing, but if it happens I always let it flower if I have room in my garden to do so. I had such a good time last year taking pictures of all the insects around my onion flowers. 

If you don’t have to take out your lettuce after it bolts to plant something else, let it flower to help the rest of your garden. I hate when broccoli starts to flower (because that means no broccoli harvest), but sometimes it happens and I leave the flowers for as long as I can.

The flowers of bolting vegetables attract the mature insects that will lay eggs. When the eggs hatch, the larvae are usually the ones to eat the bad pests. 

flowering carrot attracts beneficial insects

Cover Crops to Attract Beneficial Insects

Include cover crops that will create a habitat for the good insects that you want in your garden. Letting it go to flower really does this well. I’ve used buckwheat as a mid-summer cover crop, and I’ve been amazed at the beneficial insects it has attracted. Crimson clover is also a good cover crop for this purpose. If the good guys have a place to live, they will feast on the bad pests.

flowering buckwheat attracts beneficial insects

 

Principle 3: Test Specific Companion Planting Combinations for Your Troublesome Insects

I say “test” because what works in my garden may not work in yours. I have heard in several places that onions would repel cabbage worms. When I tried it in my garden, I had more cabbage worms than I usually do! What works for one garden may not work in another so test some combinations.

Herbs to Deter Cabbage Worm and Cabbage Looper

According to a study from Iowa State, whenever thyme was planted around crops susceptible to the cabbage worm and cabbage looper, it was the best at keeping them away. Following thyme was nasturtium and onion

companion planting herbs to deter cabbage worm

Herbs to Repel Squash Bug

The same study found that marigold planted near zucchini plants helped prevent damage from the squash bug with nasturtium being another top deterrent. 

Herbs to Repel Tomato Hornworm and Armyworm

Beds planted with basil and thyme were best able to repel the yellow striped armyworm. A different study showed that basil helped to repel the tomato hornworm as well. 

companion planting basil to deter tomato hornworm

 

Principle 4: Stop Using Pesticides

Throw out your chemicals! Even your organic pesticides, while they may be helpful in some ways, will affect your garden. Anything that you use to kill the bad pests will also affect the beneficial insects in your garden. 

Use your hands and pick or squash the bugs and eggs that you see. Use floating row covers if you need something to keep the bugs away. And work on creating healthy soil so your plants will produce enough in case you lose some to pests.

How to Organically Manage Pests in the Home Garden

Conclusion: It Takes Time

By using these principles, I’m confident you’ll find yourself on the path to an organic garden with fewer invasive pests. However, it does take time. If you’re used to spraying every insect in your garden, you’ll need to patiently wait for the good insects to notice your garden as a safe zone. If my garden is any indication, each year you’ll see a wider variety of those beneficial insects and fewer problems with destructive ones.

References:

Marigolds and Root-Knot Nematodes by Charles Overstreet and Deborah Xavier-Mis, Lousiana State University
The Truth About Companion Planting, Gardens Alive
An In-Depth Planting Guide, Mother Earth News
Companion Planting in the Vegetable Garden, University of Massachusetts Amherst
Companion Planting, Cornell University Cooperative Extension

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