Mother Nature practices companion planting, combining plants which benefit each other. Adapting the practice is one of the secrets to organic gardening. Here is my introductory article on companion planting. Louise Riotte's "Carrots Love Tomatoes" is the first book on the practice. It sells out faster than it can be printed. All other authors borrow from her. Most companion planting titles are talking about plants which look pretty together. I am listing those books in case you are interested, but those plants in them do not necessarily protect or encourage each other.