The ASTROCULTURE™ (ASC) middeck flight experiment series was developed to test and integrate subsystems required to grow plants in reduced gravity, with the goal of developing a plant growth unit suitable for conducting quality biological research in microgravity. Flights on the Space Shuttle have demonstrated control of water movement through a particulate rooting material, growth chamber temperature and humidity control, LED lighting systems and control, recycling of recovered condensate, ethylene scrubbing, and carbon dioxide control. A complete plant growth unit was tested on STS-63 in February 1995, the first ASC flight in which plant biology experiments were conducted in microgravity.The methods and objectives used for control of environmental conditions in the ASC unit are described in this paper. These include aerial zone air humidity control, temperature control, light intensity control, carbon dioxide level control, and hydrocarbon scrubbing, as well as root zone water and nutrient delivery control. The capability of the ASC unit for output and downlinking of video images from its two plant growth chambers is also described, along with its capabilities for remote data downlinking and command uplinking from the ground operation facilities.