Controlling Humidity and Temperature in Greenhouses
Successfully growing crops in a greenhouse is one thing. Maintaining consistent plant health and performance over time is another. To do that, temperature and humidity need to be actively managed throughout the growing environment.
Why is it important to manage humidity and temperature?
Plants rely on a stable environment to grow efficiently. When humidity levels are too high or temperatures swing too far in either direction, plants become stressed. Stressed plants are more susceptible to pests, mould, and mildew.
Maintaining controlled temperature and humidity supports healthy transpiration, allowing plants to take up nutrients more effectively. When conditions are right, growers can achieve better crop quality, faster growth cycles, and greater control over plant development.
What are the challenges of managing temperature and humidity?
Maintaining consistency
Keeping temperature and humidity consistent across a greenhouse can be difficult. Uneven air distribution often creates microclimates, where plants in different areas experience different conditions. This leads to uneven growth and inconsistent crop performance.
Transpiration
Temperature and humidity directly influence plant transpiration. When humidity is kept within an optimal range, moisture can evaporate efficiently from leaves, supporting nutrient uptake and plant health.
Condensation
Poor humidity control leads to condensation on plant surfaces, fruit, and greenhouse structures. These damp areas create ideal conditions for disease, mould, and mildew, which can quickly impact crop quality.
Outside influences
Outdoor conditions constantly affect the greenhouse environment. Temperature, humidity, wind, and solar radiation all play a role. Managing the balance between outside and inside air is key to maintaining stable conditions for crops.
Are temperature and humidity exclusive?
No. Temperature and humidity are closely linked. Any change in temperature will influence humidity levels, and vice versa. Adjustments need to be made carefully and monitored over time to find the right balance for each crop.
Is there a one-size-fits-all solution?
No. Climate, geography, and economics all influence how temperature and humidity are managed. A grower in the Bahamas will face very different challenges to one in Colorado.
Energy costs also matter. Access to subsidised electricity or gas can affect which systems are viable, and how intensively they’re used. The most effective approach is one that fits both the local climate and the operational realities of the greenhouse.
Methods for controlling temperature and humidity
A range of systems can be used to manage greenhouse climate. These methods are often most effective when combined.
Fans
Fans help maintain consistent air movement throughout the greenhouse. Horizontal Airflow (HAF) fans are a cost-effective way to eliminate microclimates and keep crops growing evenly. Extraction fans exchange warm, humid air with cooler outside air, helping to reduce both temperature and humidity.
Vents
Ventilation allows excess heat and moisture to escape naturally. Roof vents rely on convection, allowing warm air to rise and exit the greenhouse. Sidewall vents increase airflow while protecting crops. When using automated ventilation, monitoring outdoor conditions is essential to avoid introducing unfavourable air.
Wet walls
Wet walls are an active cooling method commonly used in large commercial greenhouses. Water flows through the wall and evaporates as air is pulled across it, lowering temperatures by 10–15 degrees. Because wet walls increase humidity, conditions need to be closely monitored, and water supply reduced if humidity rises too high.
Shade cloths
Shade cloths reduce solar heat load by limiting light intensity. The weave density affects both temperature and humidity. Looser weaves help manage excess humidity, while tighter weaves retain heat and moisture. Shade cloths are often used alongside ventilation and airflow systems to maintain balance.
Radiant heating
Radiant heating systems use hot water circulated through pipes to warm plants and surrounding air. By controlling water temperature, growers can influence both root zone and ambient temperatures, making radiant heating particularly effective for vine crops.
Fogging
Young plants and vegetative crops often benefit from higher humidity. Fogging systems introduce fine droplets into the air to raise humidity levels. High-pressure fogging systems create micro-droplets that increase humidity without damaging crops, unlike lower-pressure misting systems that can cause water to settle on leaves.
Bringing it all together
Temperature and humidity control is rarely achieved through a single solution. Fans, ventilation, cooling, shading, heating, and humidity systems all influence one another. Understanding how these systems interact is essential for maintaining consistent conditions and healthy crops.
Related greenhouse climate topics
You may also find these guides useful:
Managing greenhouse climate is about understanding how changes in one area affect the whole system. Bluelab works with growers to help interpret temperature and humidity data in context, so adjustments to ventilation, cooling, or heating are made with confidence, not guesswork.
