On the Causes of Plants

On the Causes of Plants (in Greek, Περὶ φυτικῶν αἰτιῶν; in Latin, De causis plantarum) is one of the most important works by Theophrastus (c. 371-286 BC) on plants and one of the most prominent contributions to botany in antiquity and the Middle Ages. It comprises six books. The first describes how plants reproduce and propagate, including grafting techniques. The second deals with environmental changes affecting plants, in effect a treatise on meteorology and climate, and notes that growth is reduced in dense populations. The third covers changes caused by cultivation: choosing suitable soil, spacing between trees, fertilizers, weeding, the importance of sowing at the right season, and some cereal diseases. The fourth addresses the origin and spread of cereals. The fifth examines natural and artificial influences on plant growth, disease and death. The sixth concerns the smell and taste of plants.

The work is usually regarded as a companion to Theophrastus's Historia plantarum, which describes plants themselves. Where that work is mainly descriptive, On the Causes of Plants seeks to explain the processes that affect them. The exact date of its composition is unknown.