No, A typical cannabis plant can use up to around 2000ppm co2, while the atmosphere contains only around 300ppm co2...dry ice is frozen co2, so as it "evaporates" it will increase the level of co2 in the room....this is assuming the room is sealed or a closed system. Adding co2 will absolutely enhance the grow, but you want to be able to control it and just melting dry ice is not a very controllable thing. There are other ways to generate co2, vinegar and baking soda, beer kegger tanks, and others, but unless you have a pretty big grow room, it's best to just go sit in there and sing to them several times a day....you are a co2 generator also! Remember co2 is heavier than air so you'll be wanting to dispense it from above the canopy, i.e., set your dry ice up on a shelf above the plants. Also the plants only need the co2 during photosynthesis, so no point in doing this during the dark cycle. Also if you go the tank route, 3000ppm co2 can suffocate you and your plants, so be careful and don't overdo it and dry ice can burn the crap out of you!