WHAT IS THE IDEAL TEMPERATURE FOR A GROW ROOM?

Getting the temperature right in your grow room is extremely important as a grower because it affects your plant's ability to photosynthesize and grow.

Photosynthesis is comprised of a variety of processes that are either light-dependent or light-independent. Temperature affects the light-independent process of photosynthesis, either increasing or decreasing the rate of photosynthesis.

The light-independent reactions of photosynthesis take place in the stroma-fluid surrounding the grana (stacks of thylakoids) in chloroplasts. These reactions are catalyzed by specific enzymes which work best at certain temperatures. Hence, plants growing in ideal temperatures will photosynthesize faster than plants grown in temperatures that are too high/low.

In general cannabis plants grow best at temperatures between 20-30°C (70-85°F) during the day. Growers tend to agree that the ideal temperature is around 25°C (or roughly 75°F). At night, cannabis plants like slightly cooler temperatures of roughly 17-20°C (62-68°F).

TEMPERATURE'S EFFECT ON PLANTS

Plants are fairly self-sufficient, but when it comes to temperature they are at a disadvantage. Even though it is vital to their health, plants can't create their own heat. Unlike animals and humans, a marijuana plant is entirely dependent on its environment.

How does a plant get warm?

A plant's temperature develops from a combination of external light, external temperature, and the amount of evaporation. A plant's exact temperature is not something you can read on a thermometer, but it is a definite measure of health.

Marijuana plants won't usually die from being too hot, but their growth can slow from it. High external temperatures (above 80 degrees) while flowering will not only slow down bud growth but also reduce their smell and potency. If you care about growing buds with plenty of cannabinoids, you need to be sure the external temperature is kept under control during the flowering stage.
The quality of your buds is reason enough to care about temperature, but there are many more.
You also should care about their health.

In general, too much heat causes plants stress.

If your plant gets too warm, photosynthesis is impacted, enzymes activity decreases, and fewer proteins are produced. Some proteins even break down. If this continues long enough, your plant can die.

MANAGING THE TEMPERATURE

So, you've established the optimum temperature to grow at, but how do you accurately retain that temperature in the face of fluctuating external temperatures and through your lights on/lights off phases?

Well, without wanting to sound too obvious, the first thing you will need is a thermometer to enable you to keep an accurate track on the temperature (you can browse our selection of thermometers and hygrometers here).

How you manage the temperature will depend on whether you use a grow tent or you are using a room in your house for growing.

By using a room in your house, you will have to be more proactive in managing temperature as it will be subject to greater fluctuation. This is because your walls are unlikely to be sufficiently well insulated to be able to maintain the temperature at a constant level required for consistent growth.

As the outside temperature changes, both between daytime and night and across the seasons, the temperature of your grow room will also change.

A marijuana grow tent, to a large extent, mitigates against this issue by providing a more easily controlled environment for your plants. They come in all shapes and sizes, meaning you're not restricted by the size of the crop you want to grow.

UNDERSTANDING YOUR GROW LIGHTS & HEAT THEY PRODUCE

Your grow lighting system is going to be the largest contributor to your grow tent's temperature.
So if you find yourself struggling with temperature issues, you need to look at your lighting setup first.

All lighting systems have unique ways they affect your grow room's temperature. To successfully control temperatures, you need to know how your lights do this. 

What you need to know: To spare you a headache, know that for the most part, more watts equals more heat regardless of what light is producing the watt. Remember this rule: Watts in = Watts out.
A 600 watt LED at the wall, will generate around the same amount of heat as a 600 watt HID.

Watts does not mean the amount of light produced.

LED grow lights are considered to produce less heat because you need fewer watts to match the amount of light an HPS grow lights produces - they're more efficient.

HEATING LIFE HACKS

Sometimes, all we need to do is lower our temperatures only a little bit, so here are my favorite life hacks for lowering temperatures without having to spend any money.

Run your lights at night - This one can also save you money as well, as some power companies have lower nighttime electricity rates. Remember to watch for light leaking into your grow tent as this can cause serious damage to plants in flowering. Most flowering plants need a minimum of 12 hours of uninterrupted darkness.

Change light schedule - Many growers are seeing great results running their plants under 18, 20, and even 24 hours of light a day when in the vegetative growth stage. However, the 16/8 light schedule is a classic for a reason. While running your lights longer may increase yields, you may end up hurting yields if your temperatures get too high from the extra hours of light.

Plan your grows according to season - Most plants can tolerate at least 10-15 degrees more heat when they are in veg compared to when they are flowering, but flowering plants want more light causing a catch-22. If you're fighting heat in flowering, try germinating in mid-late summer so the plant is flowering in the winter. Full spectrum LED grow light provides plants in all stages from veg to flower with everything they need in the natural sunlight. 

Use an oscillating fan or clip-on fan - Sometimes all you need to do is get stagnant air moving around in your tent. Most people have a small fan or two lying around in their house. Or, just grab a clip-on fan while you're here. They're cheap and don't take up much space at all, and will help disperse heat.

Changing Where You Grow - Heat rises, and if you live in a two-story home and/or have a basement, then you'll notice a large difference in temperatures when moving through the house. I can reduce my grow tent's temperature by over 10 degrees simply by moving it from the upstairs to the basement.

Different type of grow light - Quantum boards LED grow light run much cooler than other LED panels, so the fixture doesn't even need fans. Passive cooling is all you need. Not only does that mean silent operation, it also means a longer lifespan.

IN CONCLUSION

Temperatures all connect to get you the yield you want, and if there are conflicting temps in your grow room your plants can suffer. If canopy's too high, then it's likely soil's too high so your plants can burn. If the water's too hot but your canopy is right, you could be messing up your roots or exhausting your plant- the bad combos are endless. There's always a little wiggle room when it comes to correct temps, so the key is listening to your plants and making sure you give them they temperatures they like, not the temps they can withstand. Remember: just because a plant can withstand high or low temps doesn't mean you should subject them to unhealthy conditions.