The comfort band
Target
About 40 to 55 percent relative humidity
Too dry
Chronic mild wilt and necrotic leaf tips
Too wet
Fewer everyday stress signs, but flowers become easy targets for mold that can ruin a crop overnight
Clones
Propagation rooms are an exception. Rosenthal keeps them near 75 to 80 percent
Why sealed rooms go wet
Plant water: Transpiration and evaporation raise humidity in any closed space within hours.
Indoor default: Indoor growers more often fight excess moisture than desert-dry air.
First fix: Open a window or add a small exhaust fan before you buy a machine.
Closed rooms: A dehumidifier is the tool when you cannot vent.
Dehumidifier habits
How it works
Moisture condenses on cold coils, the same idea as a refrigerator
Part-time
Many rooms only need a few hours a day
Dark-cycle run
Run it when lights are off to ease the electrical load
Power
Even a compact unit that can dry a large room may draw about 15 amps
Controllers and filters
Sequence
Climate controllers can prioritize temperature, humidity and CO2 so devices do not fight each other
Intake filter
Screen incoming air so you are not importing spores while you vent moisture
Flower priority
Once buds pack on, humidity control is crop insurance, not a comfort setting