Why it matters
The plant doesn't regulate its temperature: it lives at the air's. Temperature decides how fast it works (photosynthesis, growth) and humidity decides how much water it loses through the leaves. Indoors, you build the climate yourself.
The ideal by stage
Seedling: 22 to 26 °C and 65 to 75 % humidity.
Vegetative: 22 to 28 °C and 50 to 65 %.
Flowering: 20 to 26 °C and 40 to 50 % (the last weeks, down to 35-45 %).
At night it's best for it to drop a few degrees, but not more than 8 or 10.
What happens if it goes out of range
Over 30 °C: the leaves fold, it loses water fast and the buds come out loose and with less aroma. Over 35 °C damages it.
Under 15 °C: it grows slower; under 12 °C, at half speed. Under 10 °C it gets damaged; some strains turn purple in the cold.
High humidity in flowering: mold (botrytis, powdery mildew). Very low humidity in seedlings: they dry out and stall.
Where the heat and humidity come from
Lamps heat things up (more in a small spot), plants transpire and add humidity (more plants, more humidity) and the night cools and dampens. The air outside the spot also matters: in winter the house is colder.
The gear
Extractor: pulls out hot, humid air and brings in air from the house. It can't cool more than the air coming in.
Dehumidifier: takes water out of the air. Key in flowering.
Humidifier: puts out vapor. For seedlings and clones.
Heater and air conditioner: raise or lower the temperature.
Controller: a brain that measures and turns the others on or off by itself.
▲ Pros
- With the right climate the plant grows stress-free
- Less mold in flowering
▼ Cons
- Each equipment that's on uses power every day
🎮 Practice it in UnderGrow
Indoors the climate comes from the house (~15 °C in winter, ~25 °C in summer; a bit cooler in a cold place and warmer in a hot one), the lamps, the plants and the night, and it goes from 13 to 33 °C all year (heat above 35 °C and cold below 12 °C only happen outdoors). You buy the gear for each spot (shop › gear) and turn it on by tapping equipment › (on the panel): the dehumidifier leaves humidity at 45 %, the humidifier raises it to 70 %, the heater raises the temperature to 22 °C if it drops below 20 °C and the ac lowers it to 24 °C. Equipment uses power only when on (the lamps and the timer don't), and it's paid at 00:00: if you can't afford it, you end up owing (your money turns red). If the debt goes over your limit (tap your money to see it; it grows with your equipment), your power is cut until you pay; the controller runs them by itself according to the stage.
▶ Play free