The Right Environment the right environment is critical for your garden. Key elements to a successful indoor garden room include relative humidity, temperature, CO2 (carbon dioxide) and air circulation. The ideal humidity for a garden room falls between 40% & 60%. Some plants like higher humidity, but know that higher humidity can lead to problems with fungus and disease. Temperatures in your grow room should be between 68 – 75 F degrees. Temperature changes will lead to variations in humidity levels. Avoid drastic temperature changes over a short period of time. Your plants also will need CO2 to grow quickly and robustly. Assuming you have good air circulation/ exchange, your garden room will have between 300-400 PPM (parts per million) of CO2; higher CO2 levels will accelerate growth rates up to 20%. If you choose not to supplement CO2 in your garden room, it is important to address the air circulation/exchange so that your plants will receive fresh CO2 constantly.