Achieving the best grow room conditions for temperature, CO₂, and light levels will enable you to get the maximum yield from your grow.
Extensive laboratory tests on Cannabis Sativa have determined the best temperature, light, and CO₂ levels for maximum photosynthesis and resulting growth rates.
The best light intensity for plant growth during flowering
Plant growth rate increases up to PAR (PPFD) levels of 1,500 µmols/m2/sec at optimum temperature and atmospheric levels of CO₂.
We recommend a PAR level of 750 µmols/m2/sec for your grow room. Increasing PAR above this level does not increase the growth rate enough to justify the additional energy consumed.
The PAR levels (PPFD) vs Photosynthesis (Growth Rate) for Cannabis Sativa at 30 Degrees Celcius and normal atmospheric CO₂ levels
The best light intensity for plant growth during vegging
The PAR intensity levels required during vegging growth are about half of the normal flowering requirements. We recommend a PAR level of 300 – 400 µmols/m2/sec for your grow room.
You can achieve these levels by reducing the power consumption of your grow light by 50% using a dimmer. If this is not available you can halve the number of lights (if possible) or raise the grow light to about 1.5 times the optimum hanging height.
What should the temperature be in my grow room?
The growth rate of Cannabis Sativa has been tested at two PAR (PPFD) levels and a range of temperatures. The lower PAR level at 500 µmols/m2/sec and higher at 1,000 µmols/m2/sec. At both PAR intensity levels the growth rate peaks at 30 Degrees Celcius. It is likely that the optimum temperature varies slightly depending on the plant species. However, it is generally accepted that 25 – 30 Degrees Celcius is the ideal temperature range for your grow room.
The best temperature for your grow room is 25 – 30 Degrees Celcius
How much does added CO₂ increase the growth rate?
The normal atmospheric CO₂ level is 370 parts per million (PPM). The best way to achieve this level in your grow room is to draw fresh air from the atmosphere into your grow room at a high rate. It is recommended you change the air in your grow room about 60 times per hour. At these rates, you will maintain very close to atmospheric levels of CO₂ of 370 PPM and achieve good growth. With this setup, it is not practical to achieve any increase in CO₂ in the grow room. This is because any CO₂ added to the grow room will be removed quickly with the constant airflow out of the grow room.
Atmospheric CO₂ levels are approximately 370 PPM. Doubling the CO₂ level increases growth by 30%. Reducing CO₂ by one third reduces growth by 50%
If you are recirculating used air back into the grow room the CO₂ levels will reduce and growth rates will slow. With this setup, you will have to add CO₂ to the grow room to ensure adequate growth. You will have to use CO₂ meters and a CO₂ generator to your grow room and calibrate it to achieve the desired CO₂ levels and associated growth rates.
Using the naturally higher CO₂ levels in the house to increase the growth rate
You can also use your own CO₂. Humans expel CO₂ when breathing out so the level within our homes is often twice the concentration outside. This is most common in winter months when the air circulation in homes is minimal. It’s common for CO₂ levels in the home to range from 700 -1,000 PPM. In a bedroom at night, CO₂ levels may reach as high as 2,000 PPM.