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How to Keep the Greenhouse Cool in Summer: Essential Tips and Techniques

greenhouse cooling-ystems

Written by H & B Sierke (Gothic Arch Greenhouses INC. ) 

Keeping a greenhouse cool during the hot summer months can be a challenge, but it's essential for maintaining the health of your plants. High temperatures can cause plants to wilt, slow their growth, or even lead to diseases. They can also cause heat stress, wilting, and reduced yields. This guide provides a detailed overview of various methods to keep your greenhouse cool, from shading and ventilation to advanced cooling systems. Here are some effective strategies to keep your greenhouse cool and ensure your plants thrive.

Why It's Important to Keep Your Greenhouse Cool?

Maintaining an optimal temperature is crucial for plant health. High temperatures can cause:

  • Heat stress: Leading to wilting and poor growth.
  • Increased pests and diseases: Warm, humid conditions can attract pests and promote fungal growth.
  • Reduced productivity: Plants may drop flowers or fruits under heat stress.

Ventilation Techniques

Proper ventilation is crucial for temperature and humidity control in a greenhouse. Natural ventilation involves opening doors, windows, and vents to allow hot air to escape and cooler air to enter. 

  1. Automatic Vent Openers: These devices open vents automatically when the temperature reaches a certain point. This is particularly useful if you're not always around to open the vents manually.
  2. Roof and Side Vents: Placing vents at different heights allows for efficient air circulation. Hot air rises and can escape through roof vents, while cooler air enters through side vents.
  3. Fans: Using fans can enhance air circulation. Exhaust fans can pull hot air out of the greenhouse, while circulation fans can help move air around inside.

Shading Solutions

Shade cloths are an excellent way to reduce the amount of sunlight entering the greenhouse, lowering the temperature. These cloths come in various densities, usually measured in percentages (e.g., 30%, 50%, 70%). The percentage represents the amount of sunlight the cloth blocks. Here’s how to use them effectively:

  1. Choosing the Right Density: A 50% shade cloth is a good starting point for most greenhouses. It blocks half the sunlight, reducing heat without overly dimming the environment.
  2. Installation: Shade cloths can be installed outside or inside the greenhouse. External installation is more effective at blocking heat but can be more challenging to set up.
  3. Retractable Shade Cloths: These systems allow you to adjust the amount of shade throughout the day or season, providing more control over the greenhouse environment.

Cooling Systems

Evaporative Coolers

Evaporative coolers use the principle of evaporation to reduce temperatures.

  • How They Work: Water evaporates into the air, which cools it down before circulating through the greenhouse.
  • Installation and Maintenance: Regularly clean your cooler to ensure efficient operation.

Fogging Systems

Fogging systems create a finer mist than misting systems and can quickly cool the greenhouse.

  • Differences from Misting: Foggers produce a finer mist that evaporates more rapidly.
  • Optimal Usage: Ideal for larger greenhouses or areas with extremely high temperatures

Misting Systems

Misting systems cool the greenhouse by releasing fine water droplets into the air, evaporating and lowering the temperature. Here are some points to consider:

  1. High-Pressure Misting Systems: These systems produce a fine mist that evaporates quickly, providing efficient cooling without overly wetting the plants.
  2. Timer Control: Using a timer to control the misting system can help ensure it operates during the hottest parts of the day.
  3. Placement: Place misting nozzles evenly throughout the greenhouse for uniform cooling.

Insulation and Reflective Materials

Insulating the greenhouse and using reflective materials can also help manage temperatures. While insulation is typically used to keep heat in during winter, it can also help keep heat out during summer:

  1. Thermal Screens: These can reflect excess sunlight and be pulled over plants during the hottest parts of the day.
  2. Whitewashing: Applying a coat of white paint or shading compound on the greenhouse’s exterior can reflect sunlight and reduce heat buildup.

Water Management

Managing water effectively can also play a role in keeping the greenhouse cool:

  1. Watering Schedule: Watering plants early in the morning or late in the evening can help reduce the humidity and heat stress on plants.
  2. Mulching: Using mulch around plants helps retain soil moisture and can keep the root zone cooler.
  3. Water Features: Adding a small pond or water feature can help cool the air through evaporation.

Plant Selection and Placement

Choosing the right plants and placing them strategically can help manage greenhouse temperatures:

  1. Heat-Tolerant Plants: Select plants that thrive in warmer conditions for the hottest parts of the greenhouse.
  2. Strategic Placement: Place more heat-sensitive plants in shaded or cooler greenhouse areas.
  3. Layering: Use taller plants to shade shorter, more delicate plants.


1. How do I choose the right shade cloth for my greenhouse? Choose a shade cloth based on the percentage of shade it provides and the specific needs of your plants. For example, 50% shade cloth suits most vegetable crops, while 70-90% may be needed for more sensitive plants.

2. Can I use regular household fans for greenhouse ventilation? While regular household fans can provide temporary relief, they are not designed for continuous use in a greenhouse environment. Invest in commercial-grade fans for better durability and efficiency.

3. What is the most cost-effective way to cool a small greenhouse? Using shade cloths and natural ventilation are cost-effective methods. You can also create DIY misting systems using garden hoses and nozzles.

4. How often should I maintain my evaporative cooler? Regular maintenance, including cleaning and replacing filters, is essential. Check the cooler at least once a month during peak use periods.

5. Are there any plants that can help cool the greenhouse naturally? Certain plants, like large-leafed tropical species, can provide natural shading and help lower temperatures. Additionally, using ground cover plants can reduce heat reflection from the soil.

Maintaining a cool greenhouse in the summer requires a combination of shading, ventilation, and cooling systems. Implementing these strategies protects plants from heat stress and ensures a productive growing season.