Answer: Companion plants are those that have similar growing requirements. In addition, some plants seem to enhance the growth of other plants. For example, some plants repel certain insects, some provide nutrients that benefit other plants, and some just look good when planted side by side.
Marigolds are often recommended to repel insects, protecting nearby crops. Brussels sprouts intercropped with white clover usually attract fewer aphids. You might try growing potatoes and nasturtiums for fewer potato beetles, or peppers and catnip to deter aphids. The combination of cabbage and anise might result in fewer cabbageworms. And radishes might reduce the incidence of green peach aphids on broccoli. There are entire books devoted to this topic if you want to do some more research.
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