Re: cannabis
Dry ice is frozen CO2 (solid carbon dioxide). As it warms to room temp, it sublimes (converts to a gaseous form), and replaces all the oxygen, asphixiating all animal life that requires oxygen to breathe. It won't kill the plants because plants actually take in CO2 and produce oxygen (the opposite of most animals). This is oversimplified, of course, but basically correct.
In order to use frozen/solid CO2, one must be very careful--don't touch it/handle it without skin protection, as it is MUCH colder (about -70C) than "normal" (H2O/water at about 0C) ice and will cause a severe freeze burn. Also, all animals one wants to keep alive should be removed from the enclosure before treatment.
It is very effective in killing unwanted critters while not harming the plants. After treatment, I had no beetles at all. After removing all the cups I had used to hold the dry ice and ensuring via really good air circulation (a fan) that the enclosure was fully reoxygenated, I put my BP back in and have had no problems with any unwanted critters since.
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