Companion planting is simply planting different varieties of plants next to - or close to - each other to achieve better results. Companion planting can be used to:
- Deter harmful insects
- Provide useful nutrients
- Provide structure or shade
- Attract beneficial insects
- Attract and trap harmful insects
The concept of companion planting for backyard gardeners gained a lot of popularity in the late 1970's and early 1980's, during a time when organic gardening techniques were rising in awareness and popularity. Gardening historians, however, note that the concept was used hundreds of years ago, when Native Americans planted corn, beans, and squash together for their mutually beneficial effects.
Known as the "three sisters," corn, beans, and squash were planted together for their mutual contributions to each other. Corn provided structure for the beans; beans, like all legumes, could obtain Nitrogen from the atmosphere so as not to compete with the corn for that nutrient; and, squash provided a canopy that significantly reduced weed growth among all three plants. So, rather than competing for soil nutrients, this combination of plants actually improved the nutrient availability for all of the crops.
A concept related to companion planting, and one that is often included in any discussion of companion planting, is the recognition that some plant combinations are "bad companions" that should be avoided. Perhaps the earliest recognition of this concept was the ancient Roman scholar, Varro (116 BC - 27 BC), who observed (and recorded) that nothing grew well in proximity to his walnut trees.
Folklore, Logic, Observation, and Science
Much of what has been written about companion planting has been derived from years of folklore and observation. Some of the techniques (like providing shade or structure) are simply logical. Some of these observations have been validated by scientific work; and, and indeed some of our natural pesticides are derived from plant materials. The observation that planting marigolds near tomato plants improves the tomato's performance is validated by the fact that the marigold plants' roots contain a chemical that is known to be toxic to soil nematodes that adversely affect tomato plants.
Unfortunately, some of the "science" is questionable. In the 1930's some scientists used a laboratory technique known as chromatography to predict which plant combinations were "good" and which were "bad." The laboratory observations and predictions are quoted in - indeed, may be the basis of - the best selling book on the subject of companion planting, which was published in the mid 1970's (over 500,000 copies in print); the scientists at Cornell University suggest that the "science" of chromatography cannot accurately predict which plant combinations are compatible.
Suggestions to Incorporate Companion Planting in Your Garden
• Plant marigold plants among your vegetable plants, or as a border to your vegetable garden. You'll improve your soil and you may discourage pests from the garden. Some have suggested that the strong scent of marigolds (especially African Marigolds) may even deter rabbits.
• Plant some strong-smelling herbs among your vegetables. The strong scent of herbs is thought to confuse damaging insects, which primarily depend on their sense of smell to locate their favorite food sources. And, you'll enjoy the benefit of growing some of your own herbs!
• Plant lettuce where it will get some afternoon shade from nearby taller crops, such as caged tomato plants or pole beans.
• Experiment with adding some dill, coriander, and parsley to your vegetable garden; these varieties are likely to attract beneficial insects, especially predatory wasps.
• Adding some basil near tomato plants might deter tomato hornworms. (And, basil and tomatoes go well together in the kitchen, too. See Our Favorite Tomato Recipes.)
• Avoid long uninterrupted rows of the same vegetable variety. Long rows with a consistently enticing aroma are an easier target for nasty insects; interplant some herbs and flowers as suggested earlier. This will not only confuse, and perhaps deter some insects; it may also make your garden more visually appealing. Experiment ? and, observe.
• Various mint varieties might help deter cabbage moths; note, however, that mint can be very invasive, so you'll need to maintain it, lest it take over your entire garden.
• Plant radishes among or near squash and cucumber plants, as they are an excellent "trap crop" for beetles. Radishes need very little room, germinate very quickly, and mature fairly quickly; so, you can intersperse them among squash and cucumber plantings throughout the season.
You don't need to be an expert on companion planting to benefit from the concept. Trying one or two of the suggestions listed here might improve your yield, reduce your need to spray, and make your gardening more interesting. As you become more interested in the topic, there's a lot of information on the Internet. But, remember that some of the science is questionable, and some of the folklore may or may not work every time. As always, gardening is an ongoing learning opportunity.