Interplanting Increases Vegetable Garden Biodiversity

(Author’s Note: Many of my columns for the coming winter months will be devoted to sustaining biodiversity in our gardens, both in the soil and above ground. Winter is the season to dream of next year’s garden, and this week’s column focuses on including interplanting in your plans for next year’s vegetable and small fruits garden.)

Biodiversity: a measure of the variety of organisms present in different ecosystems.

Recently, while reading about the diversity of life in healthy coral reefs, it occurred to me that garden biodiversity should be considered when planning and managing the vegetable and small fruits garden. For example, the wise gardener eschews monoculture in favor of mixed plantings. Instead of “setting the table” for herbivores and diseases by planting entire beds or rows to a single crop, she grows a mix of compatible species within each area, thus minimizing these problems while increasing area biodiversity. The increase in biodiversity of the mixed planting would include the plants themselves as well as the pollinators, herbivores (the plant munchers), and predatory insects associated with each type of plant. Taking this approach throughout the garden would result in an increase in total insect biodiversity, one major indicator of a healthy, productive food garden.

Growing a blend of two or more crops in the same row or bed is call interplanting. While each crop in the planting may yield less than it would if grown alone in the same space, the total yield is greater than would be achieved with monoculture, but only if compatible crops are chosen. Compared to monoculture, interplanting increases the complexity of the garden ecosystem while decreasing crop losses to herbivores and diseases.

I mentioned my renewed interest in interplanting and its impact on garden biodiversity to Marjorie and she placed in my hands a well-used copy of “High-Yield Gardening” (M.B. Hunt and B. Bortz, 1986, Rodale Press). In the chapter on interplanting, the authors state that interplanting schemes, through their diversity, “create complex ecosystems that imitate the rich mosaic of nature and therefore encourage spiders, toads, and other valuable insect predators and discourage the spread of crop-specific pests and diseases.”

A harvestman on a sunflower.

A harvestman on a sunflower.

Mention of the value of insect predators brought to mind the numerous long-legged harvestmen (arachnids similar to the daddy-long-legs) that frequent our garden in summer, feeding on aphids, whiteflies, small beetles, even small slugs. I recall finding one last season hiding beneath a summer squash leaf, waiting for its next meal to come near. As a response to the previous year’s explosion of cucumber beetles on all the garden’s cucurbits, I had spread my summer squash plants around the garden, interplanting them with other crops. Cucumber beetles were far less numerous in our garden last year and I give the garden’s harvestmen much of the credit.

Corn interplanted with winter squash leaves little room for weeds to grow.

Corn interplanted with winter squash leaves little room for weeds to grow.

Interplanting combinations should focus on both aboveground and below-ground compatibility. Plants that complement one another in the shape of their top growth will fill the available garden space, leaving no room or available light for weeds to grow. Corn and beans, for example, when grown together, intercept 90 percent of the available sunlight. They are also an ideal couple as far as underground compatibility, since corn is a shallow rooting crop while beans have deeper root systems. Add winter squash in the same bed and you have the traditional “Three Sisters” planting where the corn plants provide a scaffold for pole beans to climb, the beans fix nitrogen for all three crops, and the spiny leaves and stems of the squash deter raccoons and other corn thieves.

Interplanting schemes should also take nutrient sharing into account, mixing heavy feeders with light feeders. Fortunately, most interplanting schemes designed for sharing of aboveground and underground space, like the Three Sisters planting, also result in efficient nutrient sharing.

Imagine the mosaic of green in garden space shared by interplanted brussel sprouts, parsley, and spinach; a bed with plants of peppers, basil, and tomato arranged in an alternating pattern; a mixture of radishes, lettuce, and peppers filling a bed from edge to edge; or a mixed bed of lettuce and cabbage bordered by trellised peas. Some gardeners go so far as to transplant cabbage seedlings among the strawberries after the berry harvest is done.

Another interplanting scheme to consider is alternating blocks of beans (bush or pole) and radishes. This is a very effective way to keep flea beetles away from the bean leaves, as the beetles much prefer the radish leaves. The radish foliage will be riddled with tiny holes, yet still produce a decent root crop.

Leeks edging a bed of carrots and beans Leeks can be grown along the edges of a bed of beans, carrots, or both. Lettuce partners well with carrots, onions, radishes, or any combination of these crops. Onions thrive with cabbage, peppers, and spinach. Tomatoes or peppers can be interplanted with cole crops such as broccoli, cauliflower, and cabbage. And try surrounding the trellised spring peas with lettuce, carrots, and/or or spinach.

Many gardeners are drawn to interplanting as a technique for maximizing the use of garden space, and indeed this is one of the benefits. More important, I think, is the integration of this method of food gardening into the goal of maximizing biodiversity garden-wide. As biodiversity increases, so does the resilience of the garden ecosystem. When beneficial insects and arachnids are numerous, major crop losses to insect herbivores are rare.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)