Seltzer timing

How often should I use salt-free seltzer water to enrich plants with CO2?

Using seltzer water to enrich plants with CO2 is only feasible for small plants such as seedlings or clones. If large plants were sprayed it would raise the humidity of the space to unacceptable levels and it would be an expensive way to deliver CO2 as compared with a tank or CO2 generator.

As the seltzer evaporates, the CO2 does too and is absorbed into the leaves through the stomata (plant pores). The rate of evaporation is controlled by the temperature, the humidity and the breeze. Once the water has evaporated, wait five to 10 minutes before spraying again. It’s probably inconvenient for you to spray the plants every half hour or so. Even an occasional spritz will increase the photosynthesis rate for 20-30 minutes. A few spritzes a day will increase the growth rate a bit.

Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St., San Francisco, California 94117, USA. You can also email Ed at [email protected], and send queries via his websites at All featured questions will be rewarded with a copy of Ed’s new book, Best of Ask Ed: Your Marijuana Questions Answered. Sorry, Ed cannot send personal replies to your questions.