Many facilities for growing plants at elevated atmospheric concentrations of CO2 ([CO2]) neglect the control of temperature, especially of the soil. Soil and root temperatures in conventional, free-standing pots often exceed those which would occur in the field at a given air temperature. A plant growth facility is described in which atmospheric CO2 can be maintained at different concentrations while soil and air temperatures mimic spatial and temporal patterns seen in the field. It consists of glasshouse-located chambers in which [CO2] is monitored by an infra-red gas analyser and maintained by injection of CO2 from a cylinder. Air is cooled by a heat exchange unit. Plants grow in soil in 1.2 m long containers that are surrounded by cooling coils and thermal insulation. Both [CO2] and temperature are controlled by customized software. Air temperature is programmed to follow a sine function of diurnal time. Soil temperature at a depth of 0.55 m is programmed to be constant. Temperature at 0.1 m depth varies as a damped, lagged function of air temperature; that at 1.0 m as a similar function of the 0.55 m temperature. [CO2] is maintained within 20 μmol mol−1 of target concentrations during daylight. A feature of the system is that plant material is labelled with a 13C enrichment different from that of carbon in soil organic matter. The operation of the system is illustrated with data collected in an experiment with spring wheat (Triticum aestivum L., cv Tonic) grown at ambient [CO2] and at [CO2] 350 μmol mol−1 greater than ambient.