What temp should my grow room be during flowering? Full Guide for 420 Growers

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

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).

IDEAL RANGES FOR TEMP AND RH
Cannabis grows best when provided with ideal temperatures and humidity levels for each phase of growth. Staying within these limits is the challenge facing the summertime grower.

Flowering
During flowering, low humidity is important. Decrease to 40–50% RH. Over 60% can mean slowed growth and pathogen risks.
Room temperature with lights on should be 20–26°C. Lights off, 16–22°C. The goal is to imitate autumn, so temps need to be kept low.
Late Flowering
During late flowering, improvements to overall quality can be achieved by keeping temps and humidity as low as possible. Humidity under 40% RH is ideal.

Room temperature with lights on should be 18–24°C. Increase the difference between day/night temps by up to 10°C for even better results.

Too Low (Cold) Temps
Colder temps will tend to slow down growth. Temps lower than 60°F (15°C) tend to upset plant growth, and freezing temperatures will shock or even kill a cannabis plant. Some plants continue growing in the cold without signs of stress, but they often don’t yield as well as they should given the amount of light they receive.

Plants are also more susceptible to certain types of mold when it’s cool, especially if it’s damp, too. Mold sometimes occurs after frost melts and gets water all over your plants.

Colder temps and significant temperature fluctuations contribute to the over-purpling of leaves and can also reduce photosynthesis.

Too Hot Temps
When it’s too hot, cannabis can turn into a breeding ground for various afflictions and insects. While the heat does not necessarily kill the plant, it can cause it to be unhealthy. Instead of boasting a cream-colored hue, roots may turn brown and produce a slimy and mushy texture as it rots.

Because of root decay, the plant grows slowly. It concentrates on stretching while its leaves wilt and curl. Meanwhile, its tips suffer from a burn. As a result of its debility, it falls victim to spider mites that suck up essential nutrients and leave a range of orange, yellow, and white speckles.

Best Grow Light for Flower Stage

ECO Farm 30W CREE Chips Quantum Board



Red is the spectrum that is more suitable for the marijuana when it is in the flowering stage. Blue, on the other hand, is the more important color during the vegetative growth of the plant. This LED light delivers 660nm and 730nm far red of red light, which is more than enough to induce flowering.

Because this is a LED grow light, expect that this is going to last for a long time. Based on the specifications from the manufacturer, the rated lifespan of this light is 50,000 hours.