Most gardeners won't tell you this trick, but using dry ice you can generate CO2 for your garden directly at home for cheap! This works best in an enclosed tent indoors but can be done in a greenhouse setting as well. Be sure to use fans to blow around the CO2 for maximum coverage and benefit. Also, close your tent for at least 3 hours after administering the dry ice to allow your plants to absorb the CO2. Best wishes to you, and remember to handle the dry ice with care.
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DRY ICE CAN BE DANGEROUS. ALWAYS BE SURE TO HAVE ADEQUATE VENTILATION AND HANDLE PROPERLY WITH GLOVES!