In the indoor garden, the 3 most important environmental factors that must be controlled are temperature, humidity and CO2. If you can maintain proper levels, you're well on the way to big plants and maximizing your yield. Here are the basics:

Air Temperature
The ambient air temperature should be between 72oF and 76oF during the day if CO2 is not used. If COis used, the ambient air temperature should be between 83oF and 87oF during the day. At night, the ambient air temperature should be between 55oF and 65oF.

Another vital part of hydroponic growing is airflow and exchange. Proper airflow means your plants can breathe in CO2 and move the O2 (oxygen) it created out from the growing area. When using supplemental CO2 in an indoor garden, it’s best to exchange the air once an hour. If you are gardening in a basement or confined space, this exchange can be achieved by creating a vacuum that will pull out the old, hot air from the top of the room and draw in the new, fresh, cooler air into the bottom of the grow room. The objective is to produce consistent air movement. Plants need fresh air circulation to live. If you are growing in a confined space you must circulate fresh air into your growing area. This air flow will naturally supply CO2 to your plant. Make sure that you choose an air flow and CO2 system that best fits the area that you are growing in.

Here's what you need to maintain proper temperatures in your indoor garden:

Plants grow better at different humidity levels depending on what stage they are at. Humidity, when excessive, leads to mold and pests. Protect your crop by always making sure your humidity levels are appropriate.

Here's what you need to maintain proper humidity levels in your indoor garden:

Carbon Dioxide – CO2
Plants need carbon dioxide (CO2)for photosynthesis. It's one of the most important things to a plant, even before nutrients. The oxygen around us contains about 300 parts per million of CO2, but if you increase to about 1500ppm, the plants will grow MUCH faster with increased yield - about 30%! It's important to note that when you're supplementing with CO2, you will need an area (or tent) that is air-tight.

Small Grow Rooms
Bottled CO2 is perfect for small areas up to around 12' x 12' x 8'. CO2 tanks are available in several different sizes, but the most common size used for enriching grow rooms is a 20lb tank. In addition to the CO2 tank, you will also need to purchase a CO2 Enrichment System to properly dispense the CO2. The enrichment system attaches directly to the CO2 tank with either a wrench or channel locks. Most enrichment systems consist of a pressure regulator and gauge, a solenoid valve, and a flow meter. The flow meter allows you to adjust the amount of CO2 coming out of the tank, and the solenoid valve allows you to attach a timer or other device to turn on and off the flow of CO2, thereby maintaining the desired level of CO2 (usually around 1500ppm).

If you are using a CO2 tank with an Enrichment System, to determine the proper CO2 level and flow rate for your needs: Determine the volume of the room in cubic feet (CF). This is done by multiplying the length by the width by the height of your room. If your room measures 5’ long by 5’ wide by 8’ high, then your total volume is 5 x 5 x 8 = 200 CF.

Determine what your desired level of CO2 is and subtract the existing amount of CO2 that’s already present in your room. Most growers prefer about 1500ppm (parts per million) of CO2. Plants will respond to up to 2000ppm, but this amount is generally not used since plants will utilize such high levels only if every other aspect is in perfect balance (which is extremely difficult to achieve). Because there is generally about 300ppm of CO2 already present in the air around us, you will need to add 1200ppm in order to reach your target level of 1500ppm.

Determine how many CF of CO2 you need to inject. Multiply the volume of your room by the amount of CO2 necessary to raise the CO2 ppm to the target level: 200 CF x .0012 (1200ppm) = 0.24. Therefore, in order to raise the CO2 level in your grow room to 1500ppm, you will need to inject 0.24 CF.

Determine the flow meter setting. Assuming that after 3 hours CO2 levels will return to normal due to plant use as well as leakage, we will divide the 0.24 CF of CO2 into three 1 hour increments. 0.24 CF divided by 3 = 0.08 – approximately 1/10 CF. Therefore, every hour a 200 CF grow room needs 1/10 CF of CO2 in order to bring it back up to 1500ppm, and so your flow meter should be set to 0.1 SCFH (Standard Cubic Feet per Hour).

Medium to Large Grow Rooms
CO2 generators are generally more expensive than CO2 tanks and also produce a small amount of heat, but they offer several advantages. Generators operate on either propane or natural gas, both of which are less expensive and more available than bottled CO2. Propane generators can operate using just about any propane tank, including the small ones used for barbecue grills. Some growers use the natural gas in their home and attach a natural gas generator, which not only saves the labor of swapping out empty propane tanks, but also saves money since natural gas is cheaper than propane.

Some generators are vented so you can attach an exhaust fan and eliminate some of the heat they produce. It is highly advisable to use a
digital CO2 controller with a CO2 generator as it is fairly easy to go over 2000ppm of CO2 when using these burners. A digital CO2 controller will keep the CO2 levels within the optimum range and will not allow the generator to deviate from that range.

It’s important that the correct CO2 generator is purchased for your specific grow room size. If you purchase a generator that is too small, it would burn for too long and heat the grow area excessively. To determine the correct generator size for your grow room, first determine the volume of your room in cubic feet as described above. As an example, let’s assume your grow room is 2,000 CF.

Next, determine what your desired level of CO2 is and subtract the existing amount of CO2 that’s already present in your room as described above. Using these figures, determine how many CF of CO2 you need to inject. 2000 CF x .0012 (1200ppm) = 2.4. Therefore, in order to raise the CO2 level in your grow room to 1500ppm, you will need to inject 2.4 CF every 3 hours or 0.8 CF every hour.

Each generator will list a CO2 output per hour in CF (CFH or SCFH). For this example, let’s assume the generator will output 12 CFH. This translates to 0.2 CFM (cubic feet per minute). Since you need to inject 0.8 CFH into the grow room, you will run the CO2 generator for 4 minutes every hour. Ideally you want to keep the burn time as short as possible, preferably 10 minutes or less.

Here's what you need to maintain proper CO2 levels in your indoor garden:
Want to set up the best indoor growing environment? Take the 1 hour Grow Op Setup class or check out the other topics in the GYOstuff Learning Center.
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