CO2, carbon dioxide, is an non-flammable gas found in the air at concentrations of about 350 parts per million (ppm), or .035%. Plants use it in the process of photosynthesis, breaking the molecular bond between the carbon and oxygen using light as the energy source. When CO2 levels fall below 150 ppm, photosynthesis virtually stops and the plant stops growing. Certain plants, including cannabis, can utilize light more efficiently in the presence of higher concentrations of CO2. The brighter the light, the more efficiently the plants use the gas. In a 4' x 4' area, a 1000 watt high pressure sodium (HPS) lam has an input of 60 watts per square foot (psf). In this environment, plants can use as much as 2000 ppm. Plant growth increases, maturation speeds up and ultimately bud weight increases.
Before adding more space and additional lights to increase harvest, a good CO2 system should be installed.
In your letter you said you didn't want to spend a lot of money on a system. However, even for a single light 400 watt system, CO2 pays for itself in the first crop. The best systems continuously measure the amount of CO2 in the atmosphere and regulate delivery accordingly. These actually save you money and produce the best crops, so I highly recommend them. You can make a homemade system that uses bicarbonate of soda and vinegar or the fermentation of sugar. They are actually more costly to operate because of the cost of the ingredients, they release CO2 in an uncontrolled way so much of it is wasted, and they are time-consuming to keep going and can be messy.
As far as using a candle to make CO2, that is a very unwise idea. Even a candle in an enclosed dish is an open flame. It is an accident waiting to happen and could cause a fire under unusual circumstances.
Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St, San Francisco, CA 94117, USA.
You can also email Ed at AskEd@cannabisculture.com and send queries via his website at www.ask-ed.net.
All featured questions will be rewarded with a copy of Ed's book, The Big Book of Buds.
Sorry, Ed cannot send personal replies to your questions.