Keeping Good Company
by Jennifer Rensenbrink
When I was a new vegetable gardener, I read lots of books on companion planting. However, when I took the Minnesota master gardener course, I learned that science couldn’t prove much of what those books asserted—do carrots actually love tomatoes? I held off on recommending those books to the public, but I kept experimenting at home with interplanting, polycultures, trap cropping and other companion-planting methods.
Imagine my delight when Jessica Walliser’s book Plant Partners: Science-Based Companion Planting Strategies (Storey Publishing, 2020) came out. I was happy to see a scientist’s take on companion planting—the book provided both validation that some of what I was doing had merit and some great new ideas to try. Let the experiments begin!
All Together Now
I have a very small garden. I experiment every year with interplanting, trying to find ways to fit two or more vegetables into one area, or to grow edible plants that are also pretty flowers, like okra and sunchokes.
One of my favorite interplanting strategies is to scatter a mix of mustard greens, collard and kale seeds in my garden in April. As the seeds sprout, I thin them, enjoying the baby greens and using the mustard greens first. I keep pulling and thinning until I’ve achieved proper spacing, then allow the last few collards and kale to grow to their mature size.
I’ve interplanted many different plants with great results, from shallots and strawberries to jalapenos and holy basil to chamomile and leeks. They may not necessarily “love” each other but their growth habits complement each other and they grow well together, giving me more harvests from my small space.
Cover cropping was another strategy that was validated in Walliser’s easy-to-follow book. Winter rye, one of the cover crops she recommends, has allelopathic tendencies—it produces chemicals that discourage other plants from growing nearby. This helped explain results I’d seen several years ago, when I inherited an impossibly weedy community garden plot. A friend advised me to plant a mix of winter rye and hairy vetch in fall. (This mix can be purchased from High Mowing Seeds.) It would grow a bit, stall out for winter, then start growing vigorously in the spring. Two or three weeks before planting my vegetables, I would turn it over to decompose. Not only did it significantly reduce the number of weeds I had to contend with, but it brought the soil back to life in a big way.
Another eureka moment I had while reading the soil-building section of this book was about cucumbers, which are also allelopathic and can even affect each other if they’re planted too closely. I realized that I’d made this mistake in my garden—trying to cram four or five cucumber plants where I really ought to have used one or two. I planted far fewer cucumber plants in 2021 and my harvest was great—the plants were far bushier and more vigorous than I’d seen in recent years.
Walliser also has some great suggestions for plant companions that benefit each other through nitrogen transfer, such as alternating rows of green beans and potatoes so that the potatoes benefit from the nitrogen nodules on the beans’ roots. I tried this in 2021 and really liked how it worked. In addition to the extra nutrition boost that the potatoes received, it was a great space-saving concept.
In 2022, I’ll be creating new raised beds for my raspberries and plan to try white clover, another nitrogen-fixing plant, as a living mulch.
Plants can also help each other by providing structure, Walliser notes. I tried one of the recommended combinations last year: Sunchokes (Jerusalem artichokes) and cucamelons (Mexican sour gherkins), the tiny cucumbers that look like a miniature watermelon. The tall, sturdy sunchokes provide support to the delicate cucamelon vines. Unfortunately, I planted the cucamelon seeds too late; by the time they sprouted, my sunchokes were over a foot tall and shaded them out. Timing matters.
Plants that attract beneficial insects, such as chamomile and other herbs, are also good companions, Walliser says. I’ve experimented with interplanting chamomile with various vegetables for several years. Last year, I grew chamomile interplanted with leeks; although they don’t necessarily benefit each other, they also didn’t hinder each other. The leeks didn’t get large until after the chamomile was pretty much done.
Another insect-control strategy she suggests is interplanting cole crops, such as broccoli and cabbage, with dill, chamomile or hyssop to control cabbage worms. I’ve done this for several years and it’s been a game-changer. I used to spend hours each summer handpicking cabbage worms. I’ve not pulled a single one for at least three years with this method—and I still see cabbage worm moths in my garden all summer long. I prefer to use dill, but I also have lots of anise hyssop all over the wildflower gardens that surround my vegetable patch.
Dill sets seed prolifically, so I scatter the seed all over the vegetable garden as I’m harvesting. Dill plants that emerge in the wrong spots can be moved, and I always have plenty to spare. By letting it grow around my tiny vegetable plot, I ensure that I’ll bring in the friendly beneficial insects that eat cabbage worms.
Planting native flowering plants, annual flowers and herbs near your vegetable garden is another of my favorite pest-control strategies that Walliser backs up with science. Place pots of nasturtiums all over your yard. Grow plenty of dill, fennel and cilantro and let them go to flower. Add mint-family plants such as anise hyssop and bee balm. Attract plenty of bumblebees with brown-eyed Susans and purple coneflowers. Create habitat by leaving dead foliage and leaves in place over the winter.
Surrounding my vegetables and fruits with habitat has made them healthier and easier to manage—and watching the daily insect and bird drama unfold is endlessly fascinating. This book both showed me scientific proof for some things I knew were working, but also gave me new things to try.
I can’t recommend Plant Partners enough. Although I’m a relatively seasoned gardener, it would also be a great introduction to these concepts for a new gardener. And who knows? Maybe this year it will help me fit just a few more varieties of plants into my yard.
Jennifer Rensenbrink somehow has a miniature prairie, vegetables, herbs and several fruit trees and shrubs in her tiny Minneapolis yard. Find her on Instagram at @jenniferrensenbrink.