Temperature
The high-pressure gas lamps we use for cultivation cause a considerable amount of heat in our closed-off grow space. This heat can be damaging to the plants. In the first place, we have to make sure the plants are not too close to the lamps. A distance of approximately 40 centimeters (for 400 Watt lamps), or 50 centimeters (for 600 Watt lamps) is good. The lamps also warm the air in the room. This heat must be discharged via the ventilation system. Cannabis seems to grow best at a temperature of 25 to 26 degrees Celsius. This temperature must not be allowed to rise any higher in grow rooms where no CO2 enrichment takes place. When working with bottled CO2, or even a CO2 controller, the temperature can be a little higher; 27 to 29 degrees. When working at higher temperatures, the RH must be closely monitored. Every 10 degree rise in temperature means that the absorption capacity of the air nearly doubles (see Section 5.3). In the dark period, the temperature may drop a little, but not too much. If the temperature is too low during the dark period, molds have a better chance A temperature of approximately 20 degrees Celsius is ideal for darkness. In order to maintain an optimal temperature, you need a discharge ventilator. The discharge ventilator has a double function: refreshing the air, and drawing off the heat. As described earlier, the capacity has to be great enough to replenish the air content of the grow room at least thirty times every hour. Accordingly, when working at higher temperatures (by adding CO2), the plant needs more water and more feeding. Remember the law of minimums. We can raise the CO2 supply, but if we don’t give extra water and extra fertilizer, plant growth adapts itself to the aspect of poor care.