It is well known that a CO2 level in the garden's air between 700 and 900 ppm improves crop development and yield. Most plants grown for their beautiful flowers or foliage optimally develop at about 800 ppm. Roses are distinctive as they require about 1200 ppm in carbon dioxide concentration for best results. For many fruits and vegetables, the ideal CO2 level in the garden should be at least between 1000 and 1200 ppm.