Polyphony in the Garden
Written onMay 26 , 2015
“Polyphony” usually refers to music—the combination of many different voices, each with its individual tone and timbre, yet harmonizing with the whole. When I work in the garden, surrounded by vegetables, flowering plants, and herbs, with several species of bees buzzing in the big, purple, flowering clusters of anise hyssop at the ends of all the beds, and a breeze fluttering the leaves of the maples and oaks in the woods nearby, I sense polyphony at work in the natural world, as well.
Plants do “sing” to one another and to the insects in their neighborhood, in a sense. It turns out, for example, that when a tomato leaf is being chewed (loudly) by a tomato hornworm, the plant sends out distress signals in the form of volatile chemicals that react with the caterpillars’ own saliva, and this newly synthesized chemical somehow calls forth the hornworm predator, a parasitoid wasp, which attacks the caterpillar and protects the plant. Okay, maybe that’s “screaming” rather than “singing,” but it’s clear that complex communication is going on, one way or another. (The clicking noises tobacco hornworms make, as well as the “nicotine-breath” they exhale, serve to scare off predators too, but that’s another story.)
In the natural world, plants almost always live in intricate assemblages that may facilitate this kind of communication. In our own gardens, we can take advantage of this natural desire of the plants to grow in association with other species and reap a number of benefits: preventing soil erosion; attracting pollinators; confusing pest species; providing habitat for predator species (i.e. those who eat garden “pests”); minimizing the spread of disease; and, one hopes, creating mysterious polyphonies whose harmonies we have yet to fully appreciate.
Although I haven’t found documented evidence that Echinacea is particularly attractive to the Braconid wasp (sp. Cotesia congregatus), whose larvae are a parasite of the dreaded tomato hornworm, I did find that the year my tomatoes were growing next to a long row of Echinacea, I found a total of five hornworms on the tomatoes; each one was parasitized by wasp larvae. I checked each day and watched as each hormworm slowly died, consumed from the inside out by these hungry larvae—rather gruesome, but my tomatoes thrived and produced abundantly. It may be that other flowering plants nearby (such as Queen Anne’s Lace, the flowering tops of second-year carrots and parsnips, or caraway) were the real attractants for this particular species. But the general principle applies: If one integrates corridors of flowering plants throughout the garden, it’s more likely that these valuable insect predators will find a congenial home, stick around, find mates, reproduce, and help protect your crops.
When considering which plants best complement each other, I find it helpful to consult the wisdom of farmers and gardeners whose stories, handed down for generations, reflect long-term observations and experimentation. I then investigate what contemporary agroecologists, permaculturists, and farmers and gardeners of all stripes are learning in the lab and in the field. Last, of course, I plunge in, try new combinations, and discover for myself what is effective in my own gardens.
When I first moved to Vermont I found at a library book sale the venerable Companion Plants and How to Use Them, by Helen Philbrick and Richard Gregg, first published in 1966, updating a 1943 compilation by Gregg. In the introduction they wrote that in addition to fairly obvious ways that plants may interact, such as when deep-rooted plants loosen the soil for shallow-rooted companions, “there may also be the effects of excretions, odors, insect-repelling or -attracting substances, biotic compounds… These may directly influence the growth of other plants, or alter the population of microorganisms that live in the soil, or be effective in the crowded world of animals crawling and flying in and around the roots, leaves and blossoms.” It’s astonishing to learn the many ways this speculation has been confirmed in the intervening years through ongoing experiments and observation by both farmers and scientists.
After devouring the many observations recorded in this book, I adopted a system of alternate rows of eggplant, beans, and potatoes. I grow wide beds of each of these crops next to each other. According to Philbrick and Gregg, the potatoes repel Mexican bean beetles; the beans repel Colorado potato beetles (CPB); and, since the CPB prefers eggplant over potatoes, the insects migrate to the eggplant where they are easier to pick off by hand. I don’t know if any of this is true, but in all the years I have been gardening this way, I have had no Mexican bean beetles, nor any CPB, although these have been serious pests to gardeners nearby. I don’t know if my interplanting technique is the reason, but hey, if it ain’t broke…
Another combination I gleaned from Companion Plants is that of celery and leeks. These plants like similar soils, nutrients, and growing conditions. I plant a three foot wide bed with a row of leeks on the outside of each bed, in a trench. I plant a row of celery down the middle. As I cultivate the celery, I fill in the trenches, burying the bottoms of the leeks, and also mound up soil around the celery, blanching the lower parts. As they grow, the celery’s leaves shade out weeds, but they don’t grow tall enough to deprive the leeks of sunlight. Once the trenches are filled up, I mulch the beds well with hay, which keeps dirt out of the celery and leeks, and provides a haven for beneficial insects such as ground beetles.
A more recent book I love is Manage Insects on Your Farm: A Guide to Ecological Strategies, by Miguel Altieri and Clara Nicholls, with Marlene Fritz. The entomologist authors of this book provide myriad field-tested techniques for keeping “pest” populations in check. Their most important message is to increase the biodiversity of farms and gardens by integrating flowering corridors throughout the farm or garden to provide congenial habitat for predator species (as my echinacea border does) and to confuse pests by using aromatic plants that make the target species more difficult to detect. Applying this concept, I now always plant aromatic herbs such as dill, cilantro, epazote, and papalo (a wonderful herb that seems to combine the flavors of cilantro and arugula) in among my brassicas. The idea was to deter the cabbage white butterfly, parent of those ubiquitous green cabbage worms. I have to admit this has not been all that successful with regard to the worms, but these flowering herbs do attract many beneficial species that I suspect are helping to keep other pest populations in check. Both the brassica and the herbs do well, and space is used efficiently.
Another important strategy stressed in the Altieri book is the use of green manures or living mulches to improve soil conditions and to provide nutrients for subsequent crops instead of using chemical fertilizers that can harm soil microorganisms. For years I have been growing my tomatoes in a living mulch of hairy vetch. As the vetch grows, I cut it down with a hand scythe and leave the dead vetch on top of the bed to decompose. (Don’t plant your vetch too thickly or it may end up overwhelming the tomatoes.) The authors report research suggesting that tomatoes grown in a hairy vetch mulch use carbon and nitrogen more efficiently. They are thus healthier and more resistant to disease. At the same time, the living mulch prevents disease-causing organisms in the soil from splashing up onto the plants, prevents soil erosion and loss of nutrients, and enhances water infiltration into the soil.
Other crops that can be used as “living mulches” are oats and annual crimson clover. I’ve had good success undersowing brassica with oats (cutting it down as it grows and leaving it to decompose, or harvesting the “milky oats” for tea) and with crimson clover undersown to squash. After transplanting winter squash seedlings into hills, I sow crimson clover in the beds, which germinates in a couple of days. Soon I have a luscious bed of clover on which the squash can spread its runners. Later in the summer the clover blooms with beautiful crimson spikes, providing nectar for bees and looking gorgeous. Crimson clover may also work well with brassica—and some research suggests it may deter the cabbage moth. Maybe I’ll try it this year!
As Philbrick and Gregg wrote in Companion Plants, when we garden this way “we may well discover a steadily flowing source of pleasure, and be stimulated to admiration for the wonders our everyday environment can offer.” We may also discover polyphonies we never sensed before. This year, I intend to garden with my ears as well as all my other senses. I’ll let you know what new harmonies I hear.