Early Flowering (Weeks 1–3)

Target RH: 40–55%

During this stage, cannabis is still stretching (the “flowering stretch”), so it can handle a bit more humidity than late flower.

Keeping RH in the 45–50% sweet spot helps avoid mold while still allowing healthy transpiration.

Risks if RH is too high (>60%)

Encourages powdery mildew and bud rot later on.

Slows down resin and terpene production.

Risks if RH is too low (<35%)

Plants may drink excessively, leading to nutrient imbalances or tip burn.

Stresses stomata, slowing growth during a crucial transition period.

Tips for Control Humidity

Use a grow room dehumidifier or AC if your tent/room runs humid.

Increase airflow under and around the canopy with oscillating fans.

Maintain a slight VPD (Vapor Pressure Deficit) balance:

Example: At 77°F (25°C), aim for ~50% RH in early flower.

After week 3, when buds start stacking, drop RH gradually to 40–45% for mid–late flower.