The most important features to look for in greenhouse shade cloth are the shade percentage, the level of ultraviolet (UV) protection and the color. There are two types of this cloth: standard shade cloth and alumitex, and It is important to consider the features of each before purchase. The construction of the shade cloth and whether it is knitted or woven will have to be considered as well.
The shade percentage of the shade cloth you decide to purchase is its most important feature. Densities vary from 22% to 90%, and the type of plants you grow dictate the density you need. It is also important to choose a greenhouse shade cloth with a high UV protection level.
Standard shade cloth is made from UV protected polyethylene, which comes in both woven and knitted varieties. If you need to make customizations it is best to choose a knitted variety, as the woven type will fray when cut. Customization is sometimes necessary for a custom-built greenhouse or to accommodate air vents.
This type of shade cloth comes in various colors, but black seems to be the most common. Black shade cloth absorbs heat and protects against harmful UV rays, but it can also cause a rise in temperatures by transferring the heat and holding it inside the greenhouse. White greenhouse shade cloth reflects and diffuses the sun's heat and UV rays. It does not hold heat in and lowers greenhouse temperatures.
Alumitex is the second kind of greenhouse shade cloth and can be used inside the greenhouse because it is so lightweight. It is more expensive, but its aluminized threads make it extremely effective at reflecting heat and harmful UV rays. This kind of shade cloth is woven and will fray when cut, so it will need to be taped.
The size of shade cloth that you need should also be considered. Some vendors only sell standard widths, but some offer custom-cut shade cloth. If you decide to have the shade cloth custom cut, it is a good idea to look for a vendor that will edge, reinforce and insert grommets as well.
The number and kind of grommets used is another consideration. Grommets are plastic or brass rings that are inserted along the edge of the greenhouse shade cloth so that it can be secured easily. A 2-foot (about 0.60 m) space between grommets is recommended, but in an area with high winds they should be about 1 foot (about 0.3 m) apart.