APA (7th ed.) Citation

Philbrick, H., & Gregg, R. B. (1974). Companion plants: And how to use them. Watkins.

Chicago Style (17th ed.) Citation

Philbrick, Helen, and Richard B. Gregg. Companion Plants: And How to Use Them. London: Watkins, 1974.

MLA (9th ed.) Citation

Philbrick, Helen, and Richard B. Gregg. Companion Plants: And How to Use Them. Watkins, 1974.

Warning: These citations may not always be 100% accurate.