What About Companion Planting?

Companion planting is all the rage these days. But is there really anything to it?

With over 30 years of gardening experience, I have to agree with expert gardener Derek Fell: "I am not a believer in companion planting for insect and disease control. For example, I have not found that garlic will confuse insect pests like carrot flies and repel them from a row of closely planted carrots. Neither do I believe that certain plants don't like—or somehow like—each other's company. Vegetables are not like black walnut trees, which exude a poison from their roots that inhibits other plants from growing near them. In my experience, all vegetable plants planted with correct spacing get along fine together. Moreover, most repellent qualities in plants are released only when the plant is bruised." (Emphasis mine --DCS  Fell, Derek [2011-04-26]. Vertical Gardening: Grow Up, Not Out, for More Vegetables and Flowers in Much Less Space [Kindle Locations 1747-1751]. Rodale. Kindle Edition.)

Some plants compete for the same nutrients as others, and therefore, appear to be "bad companions." If there is appropriate spacing and proper levels of nutrients in the soil, all plants get along just fine together.