During the Middle Ages, knowledge about the healing properties of plants mainly came from druids and witches. These people knew about nature and healing and could treat health problems such as inflammation or small wounds with simple mixtures of leaves and herbs. But this eventually made them a threat to the Church.
Catholicism was very powerful and did not accept any solutions to disease other than prayer, obedience, and generous financial donations. Even if there was no cure available for a disease during a person’s lifetime on Earth, a great life in heaven was promised to them afterwards. So druids, witches, and their natural remedies represented a threat to this model. Labeled as evil, they were brutally eradicated.