What humidity level is ideal for greenhouse plants?
Written by
Benjamin Miller
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Proper Humidity Control forms ideal growing conditions while preventing disease. Most greenhouse plants do best at a relative humidity of 50 to 70%. The needs vary widely, as lettuce requires dryer conditions of 40 to 60%. In comparison, tropical plants require a humidity of about 90% for proper growth.
Plant-Specific Requirements
- Tomatoes need 60-80% RH during fruit development stages
- Lettuce thrives at 40-60% RH to avoid fungal diseases
- Orchids require 60-80% RH consistently year-round
- Tropical plants perform best at 80-90% humidity levels
Vapor Pressure Deficit (VPD)
- Maintain 0.8-1.5 kPa for optimal plant transpiration
- Calculate using temperature and relative humidity sensors
- Low VPD causes poor nutrient transport in plants
- High VPD leads to excessive water loss stress
Prevention Strategies
- Horizontal airflow fans prevent moisture stratification
- Dehumidifiers remove excess water vapor efficiently
- Strategic ventilation during high humidity periods
- Surface temperature management to avoid condensation
The vapor pressure deficit (VPD) is the true measure of plant moisture. 0.8 - 1.0 kPa is good for transpiration and nutrient flow. Use temperature and humidity sensors to compute the vapor pressure deficit. Automatic controls compensate for variations in conditions before the plants show symptoms of stress.
Controlling humidity effectively integrates numerous technologies. When the weather is drier, employ high-pressure fogging systems. Use dehumidifiers when humidity levels exceed the planned target. Use horizontal airflow fans that mitigate stratification of moisture. Implement this with vapor-tight greenhouse designs.
Proper management of humidity eliminates many problems commonly associated with greenhouse usage. There is less development of the disease fungus in optimum conditions. Plants transpire sufficiently to be well-nourished. Conditions of temperature control are simpler by virtue of humidity being properly balanced. The result obtained is uniform quality and higher yields from the crops.
Automation systems can maintain a steady humidity level at all times. Sensors monitor conditions every minute. Controllers can activate fogging or ventilation systems as needed. You achieve a 30% saving on water due to the accurate and precise control. Energy efficiency improves when the environment is in a state of balance.
Read the full article: Greenhouse Climate Control: Growth & Efficiency
