We can’t see it, but we, as growers, have to deal with the invisible: oxygen, carbon dioxide (CO2), humidity, heat, cold, and air movement. You have to ensure your plants are receiving the cleanest, freshest, most perfect environment – and you can’t see it.

Buy a thermometer/hygrometer. This measures your temperature and your humidity. Record your temps and humidity levels daily. Ideally, your grow room should stay below 80 degrees and around 50% humidity. If hotter and drier, spider mites enter with joy. Your plants exhaust themselves trying to release enough water through their leaves to cool down and you will have a tendency to overwater due to a wilted appearance.

Too cold and too humid and Pythium (root rot) jumps right in. Plants stop growing since their atmosphere also controls their growth.

Basically, if it is comfortable for you, your plants should be happy. So what do you do to control all this?

First, you need a source of fresh air. An opening in your room, down low, with a HEPA filter attached to a 4” fan (“intake fan”), set on a speed controller (such as a Speedster) to a low setting, is perfect. In reality, sometimes it is just an opening covered with a tight screen.

Heat must be vacated. A fan, usually 6”, (the “outtake fan”) can be attached to your wall, ducted to your light, and the air drawn out through the light. This will cool your light, removing heat before it damages your plants.

Since this fan is larger than your intake fan, it will create a negative pressure in your room, allowing for no air or heat to escape into your living area. Instead, it will flow through the stronger fan and be ducted out properly.

If your temperature is too high, raise the size of your fan or reduce your wattage. If the temperature is too low, get a Speedster and slow down your outtake fan.

If humidity becomes a problem, either too high or too low, get a humidifier or a dehumidifier from any drugstore.

Make sure your air is always moving. This mixes the temperature as well as the proportion of oxygen to CO2. The green parts of your plant need CO2, and the root needs oxygen. The plant uses CO2 during photosynthesis, which happens only when the lights are on. Generally, turn your fans off at the dark period.

A simple test kit is available for measuring CO2, or expensive yet infinitely useful controllers maintain the desired ppms. Enriching the air from the normal 300 ppms of CO2 to 1200 – 1500 ppms will cause up to 30% faster growth, provided light, water, nutrients, temperature, and humidity are not limiting. CO2 enrichment does not help increase flavor or essential oils in herbs. When temperatures reach above 85 degrees, CO2 is ineffective.

While using CO2, plants will use more water, stems and branches will grow faster, bloom initiation sites are increased, and blooms set earlier.

CO2 supplementation is great for your plants, but you must have a sealed room (no air coming in or out) and outtake fans that are timed to go off when our CO2 is being added. CO2 is heavier than air, so a fan down low pointed upward, will help keep the CO2 mixed into the air.

CO2 can be added with a generator for large rooms and greenhouses, through a tank and regulator for smaller rooms, or through a natural reaction, such as evaporating dry ice, fermentation, or a mushroom base such as Exhale. Generators provide CO2 through the burning of propane or natural gas. This causes heat but produces a lot of CO2. Tanks with regulators are calibrated for the size of the room and set on a timer to release the CO2 in measured amounts. Tanks are heavy, and the refills can become expensive if your room is too large. For small areas, bags of mushroom myclin, dripping white vinegar into baking soda, allowing bread to rise or fermenting beer in the same area will provide CO2. YOU are also a great source of the CO2, and help by removing oxygen as you breathe. Talking to your plants is scientifically beneficial, and you can check for problems while you are there.