In the Garden:
These chives will soon be companions to my tomato plants. The bed in the background is covered with black landscape fabric in preparation for planting.
Companions in the Garden
My vegetable garden style might best be described as unplanned, even haphazard. Although I recommend otherwise, I don't plan things out on paper. (I do take care to rotate major crop groups to minimize disease problems.) However, after doing some research on companion planting, I find that I've been unconsciously incorporating some of the principles in my own garden.
In a nutshell, companion planting is simply arranging plant types so that they complement each other. For example, one crop might deter pests from an adjoining patch; another might somehow improve the yield or quality of its neighbor.
The Three Sisters
One of the oldest and best-known examples of companion planting is the Native American's Three Sisters garden. The sisters are corn, beans, and squash, and they're planted together in such a way that they aid each other's success. Tall corn stalks provide support for pole beans to climb. Beans, through their symbiotic association with a type of root bacteria, fix atmospheric nitrogen into a form plants (especially nitrogen-hungry corn) can use. And large, ground-hugging squash leaves shade out weeds. (Recent studies suggest that the tall corn plants may confuse a major squash pest, the squash vine borer.) Interestingly, these plants also complement each other on the dinner table, as the beans provide essential amino acids that the corn lacks.
Modern, large-scale agriculture, with its reliance on machinery, precludes beneficial interplantings such as these. But as concerns about pesticide use increase, we're seeing a resurgence of interest in companion planting as a means to improve crop performance and minimize pest problems. Large-scale companion planting is still a ways off, but the technique lends itself perfectly to home gardens. By observing your plants, you may discover your own beneficial plant associations.
Several years ago, I noticed that flea beetles were decimating my little bok choi seedlings, and leaving my other cole crop transplants alone. Now I plant an early row of bok choi to lure the beetles away from subsequent plantings. I recently read that radishes will do the same thing, so I'll try them next year. I also noticed that Colorado potato beetles seem to prefer the self-sown tomatillo plants that sprout each year, so I leave a few of these in place when I'm weeding to attract the beetles. Now, instead of inspecting my large potato patch, I just examine 2 or 3 tomatillo plants, and squish the beetles and their larvae when I find them. These are two examples of ways to use companion plants as "trap crops."
Size and Space Compatibility
Some aspects of companion planting are just common sense. Planting lettuce on the northwest side of a taller crop, where it will receive some shade from the hot midday sun, will extend the harvest season of this cool-weather crop. A perimeter of prickly plants like cucumbers may deter rodents from feasting on the susceptible crops planted within.
If you plant flowers and herbs among your vegetable crops, you are practicing companion planting. By creating a diverse habitat, you invite beneficial organisms to make themselves at home in your garden. Dill, fennel, and other members of the umbel family are especially helpful in attracting predatory insects these predators feed on pest species such as aphids and scale. Planting fruit-bearing trees and shrubs near the garden encourages birds, many species of which consume insects.
There are a number of books on the subject of companion planting. Most recommendations are based on historical observation rather than strict scientific studies, although this may change as the need for alternatives to pesticides increases. As you observe your garden this summer, note whether certain plants are performing better than others, and what is planted near them. We can all contribute to the body of information that guides planting practices.
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