For many years companion planting has been a popular and alluring topic for gardeners. The idea that simply by planting the plants together you'll have less insects, disease and weeds sounds too good to be true. Well, in many cases it is. Unfortunately, most of these companion planting techniques are based on folklore and anecdotal experiences. Scientific research has disproven the effectiveness of many of these popular companion plants, such as marigolds.
But companion planting is making a comeback. Based on new scientific research, there are many ways that planting the right plants together, or in succession, will reduce your dependence on fertilizers and pesticides and be better for your soil, plants, family and the environment.
Plant Partners
In her new book, Plant Partners, Jessica Walliser highlights many of these new studies from around the world that show how to successfully companion plant vegetables, herbs and flowers. It starts with understanding your plant's growth characteristics and needs.
Sharing Space and Nutrients
For years I've been using interplanting techniques to save space, take advantage of different plant growth rates and sizes, and use plant root structures to my advantage. We've all grown the three sisters gardens with beans climbing on corn stalks surrounded by squash vines. This is a classic companion planting scheme where the corn provides the structure for pole beans to grow. The beans provide nitrogen to the corn and squash, while the squash covers the ground with vines which reduces weeds and helps with some of the need for watering.
Another simple way to companion plant is to interplant large growing, warm season transplants, such as tomatoes and eggplants, with fast growing lettuce, radishes and greens. By the time the warm season plants get large enough to shade out the greens, you've harvested most of them.
This also works for plants with different root sizes. I've interplanted shallow rooted onions near deeper rooted parsnips and carrots with good success. The roots of these different vegetables mine nutrients at different levels in the soil.
This also works with nitrogen-fixing legumes. We plant rows of peas in the center of our raised bed with lettuce along both edges. The peas fix nitrogen in the soil that the lettuce loves. Last year I grew kale in the center of a raised bed with rows of beans and edamame on either side. The kale transplants grew slowly in the center until the beans were finished producing. I cut back the beans, used the tops as mulch and the kale took off looking gorgeous in late summer and fall.
Controlling Pests
Most of us, though, think of using companion planting as a way to control insects. While just planting marigolds will not help in most situations, there are other research-based techniques to try.
One strategy is to lure pests away from your plants with another more desirable plant. For example, planting hubbard squash 3 to 4 weeks early and several feet away from pumpkins and winter squash entices the squash vine borer to attack the hubbard squash first. Then you can control the borer on the hubbards and your other squash are safer. You can also lure flea beetles off your eggplant, broccoli and other seedlings by planting radishes, Chinese cabbage and pak choi a week or so earlier than the broccoli and eggplant. The flea beetles prefer the radishes, Chinese cabbage and pak choi reducing the damage on your other crops. They also don't move very far, so you can plant the rows of radishes and pak choi beside the broccoli and eggplant.
You can also lure the right insects into your garden. Planting certain flowers, such as alyssum around lettuce, attracts beneficial insects that feed on aphids. To attract predators of the cabbageworm, try planting carrot and mint family flowers, such as dill, cilantro, oregano and sage. These attract parasitic wasps and beneficial insects. I always grow extra Florence fennel and dill and let them flower.
You can use companion plants to mask the scent of your plants from other insects so the plants can't be found. Nasturtiums planted around zucchini reduces the incidence of squash bugs. Basil planted in the tomato patch reduces egg laying of tomato hornworms.
Controlling Diseases and Weeds
Companion planting can help with weed and disease issues as well. Cover crops of winter rye and oats have allelopathic effects in the soil stopping weed seed germination and growth. Allow oats to naturally die in winter and cut and kill winter rye before planting veggies. Oats and winter rye also suppress diseases. When grown as cover crops previous to planting potatoes, there was less verticillium wilt in the soil.
Hairy vetch has also been found to be a good cover crop prior to planting tomatoes. Plant vetch in the fall. Once it's cut down in spring and used as mulch under the tomato plants, there will likely be less incidence of leaf blight diseases on your tomatoes.
Check out the book, Plant Partners, to find out more about how to successfully use companion planting in your garden. The bottom line is, the more diversity of plants, flowers and herbs you can grow together, the better chance you'll have in creating a healthy garden.
Until next time I'll be seeing you in the garden.
Charlie Nardozzi is an award winning, nationally recognized garden writer, speaker, radio, and television personality. He has worked for more than 30 years bringing expert gardening information to home gardeners through radio, television, talks, tours, on-line, and the printed page. Charlie delights in making gardening information simple, easy, fun and accessible to everyone. He's the author of 6 books, has three radio shows in New England and a TV show. He leads Garden Tours around the world and consults with organizations and companies about gardening programs. See more about him at Gardening With Charlie.
