Environment: The #2 Factor In Maximum Yield
Once we have obtained genetics that are pest and disease resistant and yield the desirable characteristics in good quantity we can turn our attention to “conforming the garden to our plant”.
Environmental basics can be considered in terms of what works 90% of the time. Obviously there will be exceptions to these rules as we look at fine tuning an environment for a specific strain.
Our indoor environment starts with lighting. Current debates are between the proven HID lighting and LED lighting. LED lighting has great future potential, but at this time, in my experience it does not produce the largest yields per watt. LED lighting appears attractive due to the perceived power savings, however, we calculate yield per watt. So it does not matter if you are running less power if the yield per watt is not adequate.
We used to be happy with 1 gram of dry plant material per watt of lighting. With the new double ended HID lighting technology my clients are not happy unless they are getting 1.4 grams per watt. Some clients even claim 1.8 grams per watt to be the new goal. These numbers blow all previous records out of the water. Accordingly, DE lighting is my current recommendation. Some DE lighting even comes with very intelligent controllers, going far beyond a basic timer board, into environmental control like sunrise/sunset options, high temp shut off and auto dim. There is some debate on lighting layout. Some layouts create a higher amount of light intensity which may reduce yield per watt but increase overall production, while layouts with lower intensity will generally increase yield per watt with a reduction in total production.
Whichever form of lighting we select we must arrange it accordingly in our garden. It is usually best to consult with a professional on the specifics for each particular space and application.
Now that we have selected our lighting we must control the heat load. Heat load is normally calculated in BTU (British thermal units). We have a number of choices for cooling our gardens including air conditioners, water cooled chillers and intake/exhaust systems. The cooling method selected should be accurately sized to handle to heat load produced year round.
Another essential component of the indoor environment is Co2. Simply put, if we are not enriching with cold gas or burning gas to produce optimum levels of Co2 then we MUST move lots of air in/out of the garden.
Air movement within the garden is usually achieved with oscillating fans, potentially one per light. Essentially all the plants must dance in a gentle rhythmic manner.
Lights off temperature must be maintained with heaters on heating thermostats in cooler climates and in warmer climates with a cooling thermostat set to the lights off set point.
Basic environmental parameters are 80-85 degrees F during lights on. Lights off is maintained at 70 degrees F creating a 10-15 degree differential between lights on and lights off. A humidity of 50-60% is typical, although any of these parameters can be fine tuned for a specific strain. We can develop a vapor pressure deficit chart for our selected genetics.
There are also certain circumstances that may require us to manipulate the environment for a specific reason, such as: to control vertical stretch during the first two weeks of flower we may employ a positive differential by bringing our lights on temp down to 78-80 degrees F and lights off temp up to 73-75 degrees F, or to control a spider mite infestation we might drop our lights on temp to 78 degrees F and raise humidity to 65%.