Early in life, Mohr worked in the family business. He developed an interest in botany through his great-uncle, a forester at the Denkendorf convent, and his uncle's son, a student at the agricultural college in Hohenheim. Through the self-study of several books on botany, Mohr furthered his knowledge in this area and developed a taste for natural science. Following his mother's wishes, he attended the Polytechincal school in Stuttgart in autumn of 1842. There he studied chemistry under Professor Hermann von Fehling and learned the plant world of the tropics in the greenhouses of the imperial court garden where his childhood friend, Wilhelm Hochstetter, was an apprentice.