Humidity Control

Precise humidity control is critical at every stage of the indoor growing cycle. Too much humidity encourages powdery mildew, botrytis and root rot. Too little causes plants to close their stomata, reducing photosynthesis and nutrient uptake. The key metric to manage is VPD (Vapour Pressure Deficit) — the driving force behind plant transpiration — and achieving the correct VPD for each growth stage requires active humidity monitoring and control. We stock a comprehensive range of humidity controllers, sensors and dehumidifiers for UK grow rooms.
Target Humidity by Growth Stage
Seedlings and cuttings require high humidity of 70–80% to compensate for their limited root uptake capacity. Reduce to 60–70% during early to mid vegetative growth as the root system develops. Through flowering, progressively reduce from 60% at week 1 to 45–50% by week 4 and below 45% in the final two to three weeks before harvest. This declining humidity curve is essential to prevent botrytis — a devastating grey mould that thrives in the dense, humid canopy of late-stage flowering plants.
In UK growing conditions, summer can bring periods of very high ambient humidity that challenge even well-ventilated grow rooms. A dedicated dehumidifier or humidity controller with an extraction fan output is essential insurance against humidity spikes that would otherwise risk the entire crop.
Digital Humidity Controllers
Digital humidity controllers use a precision hygrometer sensor to monitor RH continuously and trigger a connected dehumidifier, fan or humidifier to maintain your target level. Look for controllers with a tight hysteresis setting (0.5–1%) for accurate control without excessive on/off cycling. Combination temperature and humidity controllers simplify wiring and allow you to manage both parameters from a single unit.
We have been helping UK growers maintain optimal humidity environments since 2017. Browse our full humidity control range below.