Physiological and growth responses of bedding plants to substrate water content (2) were studied after calibrating ECHO moisture sensors for water content, salinity, and 2temperature of the substrate, studying substrate (peat-perlite) water retention characteristics (SWRC), and developing an automated system for maintaining distinct set points of 2. Based on SWRC, the distinct 2 treatments resulted in a broad range of water potentials (Q ). Results indicate that maximum photosynthesis, Q , and quantum3-3efficiency of leaves was highest at a 2 of 0.22 or 0.32 m@m in all species. In a separate study, when the 2 was allowed to dry down, the growth rate of a drought-3-3tolerant (vinca) and -sensitive (salvia) species declined at a 2 of 0.10 and 0.15 m@m,respectively. Bedding plants responded to low 2 by various mechanisms i.e., lower mesophyll resistance to CO transfer (e.g., petunia), robust photosystem II (e.g., vinca, 2salvia, petunia), and lower leaf osmotic potential (e.g., vinca).