This book is a regionally specific guide to understanding the soil conditions through the plants that appear spontaneously, usually called weeds. This approach of using so-called "bioinidcators" to inform management strategies is developed by Gerard Ducerf, but it builds on centuries of farmers' experiences managing weeds. In combination with soil tests, the composition of the spontaneously occuring vegetation can reveal much about the condition of the soil. Since the common bioindicators vary from place to place, we are using a Catalonia-specific guide, the second edition of which was published in 2021. A more general guide by the same author, in French, is Gaerard Ducref (1992) Encyclopédie des plantes bio-indicatrices vol. 1-3.