Keeping the greenhouse cool is accomplished by obtaining a balance of shading, ventilation and humidity. Providing the proper amount of each is the secret to a cool greenhouse. Here are some guidelines for shading:

Shading will be 40% more effective when installed on the OUTSIDE of the greenhouse. Improve cooling by suspending the fabric 4" to 9" above the glazing surface.

Shading installed INSIDE the greenhouse will protect your plants from sunburn, but because of the "greenhouse effect" the sun's energy will be trapped in the greenhouse and overheating can result. Radiant/reflective shading recommended for inside installation.

Choosing Shade Panel Size

Panel width should be at least 4 ft wider than the greenhouse, to hang down 2 ft on both sides. Panel length should at least extend the length of the greenhouse.

UV Protected Materials

Fiberglass Sunscreen is attractive and rolls up well. It has a life of 5-6 years as a roll shade, longer as a fixed panel.

Knitted polyethylene shade fabrics are popular because of their light weight and easy handling. They do roll up easily and do not unravel when cut to size. Life of the material is 5-10 years.

Charley's finished polyethylene shade panels are very durable (lasting 8-15 years) and available in a wide range of densities and sizes. See Knit Lock 40%, Knit Lock 50% and Knit Lock 62%. This material does not roll up easily. Panels come hemmed to prevent fraying and pre-grommeted for easy tie-down.

Reflective shading is recommended where exposure to sun and heat is very high. Life of 3-5 years.

Liquid Shading Compounds

Shading "paint" is popular where neat appearance is not a major concern. The compound comes as a concentrate and can be thinned with water to the desired shading density. The paint can be layered to increase shade density and to allow different shade densities across the greenhouse.

Density

A density number is the percentage of light blocked by the shade. The following can be used as a general guide:

30% - Snapdragons, Chrysanthemums, Geraniums, Vegetables
45% - Lilies, Bedding Plants, Caladiums
50% - Azaleas, Begonias, Camellias, Gloxinias, African Violets, Poinsettias
55% - Pachysandra, Ivy, Orchids
60% - Diffenbachia, Stag Horn Fern, Rhododendron
70% - Fern, Anthurium, Dracaena, Philodendron
75% - Palms, Chinese Evergreen

Experience has shown that 40 to 60% density is satisfactory in temperate zones, with the higher densities of 70 and 80%, and reflective shading, used in the Southern states. Consider using a high-density shade on the roof, and a lower density shade on the walls. A Light Meter is a valuable tool in determining the proper amount of shading.

Shade Installation

The easiest method is to drape the shade over the greenhouse and secure it with lines through grommet clips that snap onto the edges of the shade. If you have roof vents, open the vents all of the way, then drape the shade over the greenhouse and tie down with a small amount of slack. Anchor Stakes can be twisted into the ground or eye bolts can be twisted into the wood sill plate to provide another place to attach the lines. A Tie-Down Kit provides the line and 4 rope locks for easy adjustment of the shade panel.

A Roll Shade System may also be used to allow an easy way to let more light in when needed. For an idea on how to build a Roll Shade System click here.