Temperature AND HUMIDITY
TEMPERATURE
One of the most important factors in providing a healthy happy plant is to provide the plant with the correct temp for its growing phase. Plants in the seedling and vegetative phase of growth prefer higher temperatures between 75 - 80 degrees and will not grow well if the temperature falls much below these levels. Nighttime levels should be 5-10 degrees cooler than daytime levels.
Plants in the flowering phase tend to like slightly cooler temperatures from 70-75 degrees. Gradually reducing your heat levels from 75 degrees during the first few weeks of flower down to 70 degrees during the ripening phase will provide the best results.
Similarly, plants given too much heat in the flowering phase will suffer from heat stress which will hurt the plant and lead to smaller, less dense buds.
CONTROLLING TEMPERATURE
In order to control the heat in your growing environment you will need three things: a Heater, an Air Conditioner and exhaust fans. When they are used will be determined by the seasons, with A/C and exhaust fans needed in the summer and a heater in the winter.
Heater
Choosing your type of heater will depend on many things, preference, location of your grow area, etc but you need to make sure you have a heat source that can be controlled constantly to the ideal level.
A climate controlled room with its own thermostat or a standalone electric heater controlled by a digital controller with temp sensors can both work depending on your environment.
Air Conditioner
An air conditioner is a must for the summer months when the ambient temperature and the heat from your grow lights become much too hot for the plants. A window style A/C or a mini split A/C are both good choices depending on your circumstances. Portable A/C's with exhaust can work in a pinch, but tend to give off massive amount of heat from the exhaust hose which can be very hard to control and will actually add heat back into your room.
Exhaust fan
An exhaust fan can be very helpful in removing excess heat from your grow room. Exhaust fans plugged into digital controller with heat sensors will turn the fans on and off when the heat gets too high and back off when the desired range is reached. When using HID lights with air cooled hoods the exhaust fan should be set to run whenever the light is on to remove the excessive heat produced by the lights.
Depending on your setup, you may have multiple exhaust fans each set up for a different purpose. One fan for your lights, another to help remove excess heat from the room. Working together you can achieve the ideal temperature for your plants.
HUMIDITY
The other very important environmental factor that you need to control is the humidity. As with Temperature, cannabis requires very specific humidity levels during each of its grow phases to grow healthy and happy.
Plants in the seedling and vegetative phase of growth prefer higher humidity levels between 60 - 70% and will show stunted growth if the humidity falls much lower for extended periods of time.
Plants in the flowering phase tend to like slightly less between 50 - 60 % . Gradually reducing your humidity from 60% during the first few weeks of flower down to 45 - 50% during the ripening phase will provide the best results.
Too much humidity in the flowering phase will not only hurt your plants, it can increase the chances of mold growth in your buds
