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
Green Knitted Polyethylene
Shade Fabric is popular because of its lightweight and easy handling.
It rolls up easily and does not unravel when cut to size. Life of the
material is 5-10 years. See C2151 Green Knit Shade 60%. Also available
in pre-cut kits that include grommet clips and tie-down cord. See C2064 Lockknit Shade Kit.
Charcoal Fiberglass Sunscreen is made from an attractive, vinyl-coated fiberglass, and won't unravel when cut. Blocks out 55%. Weatherproof and very durable.
Excellent choice for roll shades. See C2255.
Charley's Custom Knitted Shade Panels Made from UV-stabilized polyethylene with double-reinforced border tape and brass grommets every 24" for easy tie-down. Available in a large variety of sizes.
Aluminet Custom Screen Panels made of a highly reflective, silver metalized knitted screen. It reflects excessive heat and light when hot, while holding heat energy in at night when cold. Lightweight for easy installation and repositioning. Edged with border tape and brass grommets in corners and every 24". Aluminet Panel 50%, see C2277. Aluminet Panel 70%, see C2279.
Greenhouse Shading Paint is popular where neat appearance is not a major concern. Vari-Shade Liquid Paint screens out excess summer sun, but becomes transparent during rainy weather allowing more light in. It repeats indefinitely as weather conditions change. Thin with water to desired shade density. See C2035.
A density number is the
percentage of light blocked by the shade. The following can be used as
a general guide:
30% - Snapdragons, Chrysanthemums,
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, Anthodium, Dracaena, Philodendron
75% - Palms, Chinese Evergreen
It's important to know the light requirements of your plants. Many plants that flower in the spring will last much longer if kept shaded and cool. Seed sowings also often need shade.
Make the most of the micro climates inside your greenhouse. Shade lovers can go under bench level. Use the natural shade of taller plants to shade smaller plants. Plants needing full sun can go on shelves or in parts of the greenhouse left unshaded.
Experience has shown that
50-60% density is satisfactory in temperate zones, with the high density
of 75-80% used in the southern states. Consider using a higher density
shade on the roof, and a lower density shade on the walls.
The easiest method is to
drape the shade over the greenhouse and secure it with rope 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 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.
If your greenhouse has cresting, simply place
a gooved piece of wood on top of the cresting, then drape your shade panel
over your greenhouse. This will prevent the cresting from poking holes
in your shade panel. Shade panel should be tied down loose enough for
your automatic roof vents to open and close.
Take down, dry, fold and put away for winter. Can clean with mild soap