How to Cool a Greenhouse

on September 22, 2023

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Greenhouses provide a controlled environment for growing a wide range of plants, but as any gardener knows, maintaining the right temperature is crucial. During the scorching summer months, excessive heat can pose a significant challenge. Effective cooling is essential to ensure your plants thrive without succumbing to extreme temperatures. In this comprehensive guide, we will explore various methods to cool down and maintain a comfortable climate inside your greenhouse during the summer.

Natural Ventilation

Roof Vents

Roof vents are a fundamental component of greenhouse design for managing heat. Positioned at the apex of the greenhouse roof, they allow hot air to rise and escape. You can manually open them or invest in automatic roof vent openers, which respond to temperature changes. These openers lift the roof vents when the interior gets too warm, facilitating the flow of hot air out and cooler air in.

Side Vents

Side vents are another valuable feature for cooling a greenhouse. Usually situated at or near ground level, they can be opened to allow fresh air to enter and warm air to exit. Side vents work harmoniously with roof vents, encouraging cross-ventilation and preventing the buildup of heat. Proper adjustment of side vents is vital for maintaining the desired temperature and airflow.

How to Cool Down a Greenhouse

Shade Cloth

  • Types of Shade Cloth: Shade cloth, often referred to as greenhouse film or covering, comes in various types, each offering a specific level of shading. The percentage of shade provided depends on the cloth's density. Common shade percentages include 30%, 50%, and 70%. The choice of shade cloth depends on the greenhouse's location and your plants' specific needs.
  • Installing Shade Cloth: Proper installation of shade cloth is crucial to its effectiveness. It should be stretched tightly and securely fastened to prevent flapping in the wind or sagging. Ensuring there are no gaps or spaces that allow sunlight to penetrate is essential. Properly tensioned shade cloth evenly distributes shading, preventing hot spots within the greenhouse.

Evaporative Cooling

  • Evaporative Cooling Systems: Evaporative cooling is a highly effective method for reducing greenhouse temperatures. This technique capitalizes on the cooling effect that occurs when water evaporates. Systems such as evaporative cooling pads and fans work by drawing warm air through wet pads, causing the water to evaporate and cool the air in the process. The cooled air is then distributed throughout the greenhouse.
  • Setting Up an Evaporative Cooling System: Setting up an evaporative cooling system requires careful planning. You need to install the cooling pads, position the fans correctly, and connect them to a water source. Additionally, regular monitoring and maintenance of the system are necessary to ensure it functions optimally.

How to Keep a Greenhouse Cool in the Summer

Fans and Ventilation

  • Exhaust Fans: Exhaust fans are indispensable for maintaining proper airflow and temperature regulation in a greenhouse. Typically installed on one side of the greenhouse, they expel hot air to the outside. Various types of exhaust fans are available, including traditional belt-driven fans and energy-efficient direct-drive fans.
  • Circulation Fans: Circulation fans are strategically placed inside the greenhouse to ensure even temperature distribution. They prevent temperature variations by constantly mixing the air, helping plants receive consistent warmth and preventing the formation of hot and cold spots.

Drip Irrigation

  • Benefits of Drip Irrigation: Drip irrigation not only saves water but also contributes to cooling the greenhouse. As water drips onto the soil, it cools the surrounding air through evaporation. Additionally, consistent soil moisture helps maintain a more stable temperature.
  • Setting Up Drip Irrigation: To use drip irrigation as a cooling method, you'll need to install a drip system with the appropriate spacing and flow rate for your greenhouse. The system should be set up to water your plants effectively while also providing some cooling benefits.

Cooling Strategies for Different Greenhouse Types

  • High Tunnel Greenhouses: High-tunnel greenhouses are generally more open than traditional greenhouses, allowing for more natural ventilation. However, shade cloth and exhaust fans can still be beneficial for controlling temperatures during the hottest months.
  • Polycarbonate or Glass Greenhouses: Polycarbonate or glass greenhouses may require more extensive cooling systems due to their higher heat retention. Combining shade cloth, roof vents, and circulation fans can help manage temperatures effectively.

Temperature and Humidity Management

  • Monitoring Devices: To effectively cool a greenhouse, you must closely monitor temperature and humidity levels. Investing in digital monitoring devices can provide real-time data to help you make informed decisions about when and how to cool your greenhouse.
  • Managing Temperature Swings: Maintaining consistent temperatures inside a greenhouse is essential for plant health. Rapid temperature fluctuations can stress plants and hinder growth. By carefully managing cooling systems and insulation, you can prevent extreme swings in temperature.


Keeping your greenhouse cool during the summer is essential for creating a thriving environment for your plants. By understanding the principles of greenhouse cooling and implementing the right strategies, you can ensure that your plants remain healthy and productive even in the hottest months. Whether you rely on natural ventilation, shade cloth, or advanced cooling systems, maintaining the ideal temperature is the key to successful greenhouse gardening.


How do I know if my greenhouse needs cooling?

Signs that your greenhouse may need cooling include excessively high temperatures, wilting plants, and excessive humidity. If you're unsure, it's a good idea to monitor the temperature and humidity levels regularly.

Can I use regular household fans to cool my greenhouse?

While household fans can provide some ventilation, it's recommended to use fans specifically designed for greenhouses. These are designed to withstand the greenhouse environment and provide better airflow.

What is the best shade cloth percentage for my greenhouse?

The choice of shade cloth percentage depends on the climate and the specific needs of your plants. In hot climates, a higher percentage (50% to 70%) may be suitable, while in milder climates, 30% shading might suffice.

Do I need a cooling system for a small greenhouse?

The need for a cooling system depends on factors like location, greenhouse size, and the types of plants you're growing. Even small greenhouses can benefit from ventilation, shade cloth, or simple techniques like opening doors and vents during the hottest hours.

Can I cool my greenhouse without using electricity?

Yes, you can cool your greenhouse without electricity by relying on natural ventilation, shade cloth, and other passive cooling methods. However, in extremely hot climates, some electrical cooling might be necessary for optimal plant growth.