Greenhouse shade cloths work by reflecting the sun’s rays off of the cloth or by blocking them. Natural greenhouse ventilation can cool the greenhouse to outdoor ambient temperature, and additional cooling can be achieved using evaporative cooling pads or automated ventilation. However, using shade cloth on your greenhouse provides additional cooling without increasing electricity use.

Shade fabrics come in a variety of materials. They may be woven from polypropylene, saran, polyethylene, or polyester. Shading fabrics are easy to use and lightweight. They can be purchased to provide 10-90% protection. A 50% filtration level fabric will provide about 10°F heat reduction. Shading fabric can have even better cooling performance when it is kept wet, you can do this by using misters.

Reflective shade cloth materials offer the enhanced ability to reflect sunlight and keep the greenhouse cool during the day, releasing heat at night. Shading fabric also performs better of windy days when the air is cooled slightly before entering the greenhouse, and when the interior of the greenhouse is a light color. Black or green colored fabric will conduct more heat than white material but tends to have a longer lifespan. Shade cloths can last up to 10 years if you get high-quality material. Some shade cloths are water permeable and will allow irrigation water to pass through the fabric.

Shade cloth may be woven or knitted. Woven polypropylene shade cloth is heavier than knitted and usually costs more. Woven shade cloth looks more plastic than knitted and is only available in black. If woven shade cloth gets a hole, it will unravel. Woven cloth is popular for greenhouse applications and has a 10-12 year lifespan. Knitted polyethylene shade cloth has a lower lifespan of 7-10 years and has a more fabric-like feel. Knitted shade cloth will not unravel if it gets a hole.

The percentage associated with a particular cloth indicated how much light is blocked 50% to 60% light filtration shade cloths are used very commonly. Growers with southern-facing greenhouses that receive full summer sun or growers cultivating light-sensitive plants may opt for higher protection from a 70% to 80% cloth that will only allow 30% to 20% light penetration.

Retractable shade screen systems are an option to make using shade cloth more convenient and efficient. These systems make it easy to roll back the cloth on cloudy days when it is not needed. Mechanical shade screen systems can be further automated by connecting them to a timer, thermostat, or light sensor. 4 mm aluminum and polyester screen material is typical in shade screen systems. It can provide about 10°F temperature reduction and will trap heat to keep plants warm overnight. Systems can cost $1.50 to $4.00 per square foot after installation and are mainly used by large commercial greenhouses.

Shade cloths can be attached to guide wires for manual operation where it can be drawn over the plants like a curtain. Grommets are very common features on shade cloths, and with them, a system of lines and pulleys can be run along the sides of the greenhouse, additional support lines can run-up to the center of the roof. This draw system can be simplified by hanging lines along the greenhouse walls, about 2 feet above plant height, and suspending the cloth from the line using curtain rings so it can easily be pulled over the plants or retracted. Both this system and motorized systems do not allow the shade cloth to be flush with the walls of the greenhouse. When the cloth is not flush, heat can enter through the gaps, so that is something to be aware of.

Shade cloth can be clipped or tied to the structure either on the outside, over the top of the greenhouse, or on the inside (just inside the roof, or a few feet above plant height). Installation is easily customized to fit the needs of the greenhouse. South and west exposed greenhouses especially need to make sure shade cloth is utilized and installed for optimum performance. It is best to install shade cloth once the greenhouse is constructed, but shade cloth can be easily retrofit as well.

Shade cloths with grommets will need snugger tie-downs for installation. Cloths without grommets will require clips for installation. Rope may also be needed to hang and secure the shade cloth. Installing shade cloth is fairly easy and does not require tools. Shade cloth needs to be custom fit for most greenhouses. A standard sized cloth can be purchased and hemmed or seamed together as needed to fit the space.

Insect screens can also offer plants some shade. Be aware that the percentage indicated for the net does not indicate the amount of light filtration like with shade cloth, instead, it indicates the size of the openings in the screen. Different sized screens are used depending on the insects of concern. A 50% screen is good for blocking thrips, whiteflies, leafminers, and aphids. With a 50% mesh insect screen, 20-29% shading and ample airflow will also be provided. Insect screens can be installed around the greenhouse, over intake vents, and (double screens) over service doors.

White ground cover is another greenhouse feature that will help keep the greenhouse cool by reflecting light. Ground covers are rolled over the ground in greenhouses with dirt floors. The covers are made of a woven UV resistant polypropylene material. The material allows water to drain and resists mold and mildew, and is much more sturdy than plastic ground covers. In addition to helping maintain cooler greenhouse temperatures, the ground cover will prevent weed growth without the use of chemical herbicides.