CO2

Elevating carbon dioxide levels can increase growth speed a great deal, perhaps even double it. It seems that the plant evolved in primordial times when natural CO2 levels were many times what they are today. The plant uses CO2 for photosynthesis to create sugars it uses to build plant tissues. Elevating the CO2 level will increase the plants ability to manufacture these sugars and plant growth rate is enhanced considerably.

CO2 can be a pain to manufacture safely, cheaply, and / or conveniently, and is expensive to set up if you use a CO2 tank system. CO2 is most usable for flowering, as this is when the plant is most dense and has the hardest time circulating air around its leaves. If you’re strictly growing vegetatively indoors, (transferring your plants outdoors to flower), then CO2 will not be a major concern unless you have a sealed greenhouse or growroom, and wish to increase yield while decreasing flowering time.

For a medium sized indoor operation, one approach is to use CO2 canisters from welding supply houses. This is expensive initially, but fairly inexpensive in the long run. These systems are good only if your area is not too big or too small.

The basic CO2 tank system consists of a 20 lb tank, regulator and a timer or controller. You can expect to pay somewhere in the neighbourhood of $400 to $500 for your initial set-up. After that, filling your tank will cost you somewhere in the area of $20 to $25.

CO2 is cheaply produced by burning Natural Gas. However, heat and Carbon Monoxide must be vented to the outside air. CO2 can be obtained by buying or leasing cylinders from local welding supply house.

For a small enclosed growroom, one tank could last two months, but it depends on how much is released, how often the room is vented, hours of light cycle, room leaks, enrichment levels and dispersion methods. This method may be overkill for such a small venture.

It is generally viewed as good to have a small constant flow of CO2 over the plants at all times the lights are on, dispersed directly over the plants during the time exhaust fans are off.

Opportunities exist to conserve CO2, but this can cost money. When the light is off you don’t need CO2, so during flowering, you will use half as much if you have the CO2 solenoid setup to your light timer. When the fan is on for venting, CO2 is shut off as well. This may be up to half the time the light is on, so this will affect the plants exposure times and amount of gas actually dispensed.

Environmentally, using bottled gas is better, since manufacturing it adds to the greenhouse effect, and bottled CO2 is captured as part of the manufacturing process of many materials, and then recycled. Fermenting, CO2 generators, and baking soda and vinegar methods all generate new CO2 and add to the greenhouse effect.

CO2 generation from fermentation and generators is possible. A simple CO2 generator would be a propane heater. This will work well, as long as the gases can be vented to the grow area, and a fan is used to keep the hot CO2 (that will rise) circulating and available below at the plants level. Fire and exhaust venting of the heat are issues as well. A room that must be vented 50% of the time to rid the environment of heat from a lamp and heater will not receive as much CO2 as a room that can be kept unvented for hours at a time. However, CO2 generators are the only way to go for most large scale operations.

Fermentation or vinegar over baking soda will work if you don’t have many vent cycles. However, if you have enough heat to make constant or regular venting necessary, these methods become impractical. Just pour the vinegar on baking soda and close the door, (you lose your CO2 as soon as the vent comes on). This method leaves a great deal to be desired, since it is not easy to regulate automatically, and requires daily attention. It is possible however, to create CO2 by fermentation. Let wine turn to vinegar, and pour this on baking soda. It’s the most cost-effective setup for hobby growers, for whom $400 in CO2 equipment is a bit much to swallow.

In fermentation, yeast is constantly killing itself; it takes a lot of space. You need a big bin to constantly keep adding water to, so that the alcohol levels will not rise high enough to kill the yeast. Sugar is used quickly this way, and a 10 pound sack will run $3.50 or so and last about two to three weeks. This is also difficult to gauge what is happening as far as what amounts are actually released. A tube out the top going into a jar of water will bubble and at least visually demonstrate the amount of CO2 being produced.

Try sodium bicarbonate mixed with vinegar, 1 tsp (~30cc). This will gush up all frothy as it releases CO2. Do it just before you close the door on your plants. A much cheaper way to provide CO2 is accomplished by dissolving two ounces of suger in two litres of water in a bottle [sterilized first with bleach and water, then rinsed], plus a few cc’s of urine (Hey, its not just for relieving the sting of a jellyfish bite.), or if you insist, yeast nutrient from a home brewing supplier. Add a brewing yeast, shake up and keep at 25 degrees Celsius (~70 F). Over the next two weeks or so it will brew up about ½ Ounce of CO2 for every Ounce of sugar used. Keep a few going at once, starting a new one every three days or so. With added CO2, growth is phenomenal if done correctly.

As far as a good homemade container for your CO2 machine, a one gallon plastic milk jug with a pin-hole in the cap will work just fine. Also, the air-lock from a piece of clear tube running into a jar filled with water will keep microbes out and demonstrate that the fermentation is working.

A variation is to spray seltzer water on the plants twice a day. This is not recommended by some authorities, and receives great raves by people who seem to feel it has enhanced their crop. It stands to reason this would work for only a small unvented growroom, but may be right for some larger gardens. However, It could get expensive with a lot of plants to spray.

Use seltzer, not club soda, since it contains less sodium that could clog the plants stomata. Wash your plants with straight water after two or three seltzer sprays. It’s a lot of work, and you can’t automate it, but it does keep you directly in control. Seltzer is available at most grocery stores. Club soda will work if seltzer water is not available; but it has twice the amount of sodium in it. A very diluted solution of Miracle Grow can be sprayed on the plant at the same time. One factor of using selzter water is it raises humidity levels. Make sure your venting humidity during the dark cycle, or you could risk fungus and increased internode length.

CAUTION: Don’t spray too close to a hot bulb! Spray downward only, or turn off the lamp first.

Even though CO2 enrichment can mean 30-100% yield increases, the hassle, expense, space, danger, and time involved can make constant or near constant venting a desirable alternative to enrichment. As long as the plant has the opportunity to take in new CO2 at all times from air that is over 200 ppm CO2, the plants will have the required nutrients for photosynthesis. Most small, enclosed grow areas will need new CO2 coming in every two or three hours, minimum.

Most cities will have high concentrations of CO2 in the air, and some growers find CO2 injection unnecessary in these circumstances.