Soilless potting media for controlled‐environment facilities

The combination of liquid nutrient and peat: vermiculite: gravel (15: 15: 70) medium used at the Climate Laboratory of Plant Physiology Division, DSIR was compared with a range of soilless media and nutrients. Flexibility of the medium was assessed by modifying the ratios of peat: vermiculite: gravel, as well as the source of vermiculite. Growth was found to be either controlled by the pH of the medium, or, in high‐gravel‐content media, by the pool size of available nutrient. The two sources of vermiculite differed markedly in pH, emphasising that careful quality control is essential for reproducible production of soilless media. Limitations of the standard Climate Laboratory medium are discussed.