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Achieving the best grow room conditions for temperature, CO 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. Tests were carried out on 20 samples of a high potency strain of Cannabis Sativa in laboratory environments. Light intensity, temperature and CO levels were varied to determine the best conditions for plant growth. This research was conducted by scientist, Suman Chandra and colleagues (Chandra et. al.) in the University of Mississippi, and published in 2008.

Download the article here: Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions Suman Chandra1, Hemant Lata1, Ikhlas A. Khan1,2 and Mahmoud A. Elsohly1,3

We have extracted the key information you need to achieve the best grow room conditions for maximum yield as follows:

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 will deal with temperature and elevated CO₂ levels later in the article).

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.

ppfd vs photosynth

The PAR levels (PPFD) vs Photosynthesis (Growth Rate) for Cannabis Sativa at 30 Degrees Celcius and normal atmospheric CO 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.

Grow room temperature vs growth rate graph

The best temperature for your grow room is 25 – 30 Degrees Celcius

How much does added CO increase growth rate?

The normal atmospheric CO level is 370 parts per million (PPM). The best way to achieve this level in your grow room is to draw fresh air from 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 air flow out of the grow room.

Grow room CO2 vs growth rate graph

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 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. Check out an article here on the CO₂ levels in the typical day of a person at home, work etc. https://www.co2meter.com/blogs/news/co2-levels-at-home

 

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