Plants need light, but during the summer months they can get too much of the heat energy from direct sunlight. Photosynthesis and other plant growth processes shut down when the environmental and tissue temperature gets so high that all the water taken up by the plant is used to cool the plant tissue. The greenhouse shade cloth will help cool the greenhouse when all other practical cooling techniques are being employed and more cooling is needed.
When the other temperature reduction measures such as air movement with fans and evaporative cooling have been employed, another option to cool the greenhouse is the use of a garden shade cloth. White or silver shades reflect heat and can be more effective when trying to cool the greenhouse especially when the greenhouse shade cloth is placed on the outside of the greenhouse. Black or green garden shade cloth absorbs even more heat and then can radiate it down onto the plants.