Humidity

Relative humidity

Relative humidity (RH) tells you how much water vapour the air currently holds compared with the maximum it could hold at that temperature.

Many tropical aroids grow well around 60–80% RH, although different species can tolerate different conditions.

Transpiration

Transpiration is how a plant loses water through tiny openings in its leaves called stomata. Humidity affects how quickly this water leaves the plant, so it also influences water movement, cooling and nutrient transport.

For example, low humidity can increase water loss, while very high humidity can slow transpiration too much.

Humidity management

Humidifiers can increase RH, while ventilation, air movement and dehumidifiers can help bring it down.

For a grow room, the goal isn't to keep humidity as high as possible — it's to create a stable environment with enough airflow to prevent stagnant, overly wet conditions.

Humidity stress

Very high humidity combined with poor airflow and wet surfaces can create conditions that favor fungal and bacterial problems. Leaves and substrate that stay wet for too long are especially vulnerable.

Low humidity increases water loss through the leaves, which can cause wilting, curling and dry or crispy leaf edges. Softer, thin-leaved tropical plants are often more sensitive to these conditions.

Humidity itself isn't the enemy — the combination of humidity, temperature, airflow and moisture is what matters most.