In fact, growing orchids outdoors in the summer under green house shade cloth will benefit them, as many varieties tend to flourish in the brighter light and the day-night temperature differential that they can get outdoors. Unless, of course, you grow your orchids indoors year round under high intensity grow lights. However, most of us do not have the resources or dedication to set up a professional quality orchid greenhouse. We would just like to have a few orchids whose blooms we can enjoy year after year, without spending big bucks to grow and bloom them.
A good way to take advantage of natural light is to grow your orchids indoors near a south facing window in the cold season, perhaps supplementing the available light with cheap full spectrum fluorescent lights on a timer, and maybe a humidifier if it gets very dry in your house during the winter. Then, in the summer, put your orchids outdoors under mesh shade cloth (also known as greenhouse shade cloth) in a well lit area, so they get plenty of light without being overexposed to the hot sun during the late morning or afternoon.
Your orchids can stay out till sometime in the fall, as long as the temperature remains above 50 degrees F. Light loving orchids like Cattleyas, Paphiopedilums and Oncidiums will especially benefit from this arrangement, as they may not flower if they do not get adequate light. Phalaenopsis orchids prefer lower light, but even they will benefit from being outdoors in the summer, although you could put them in a shadier part of the garden under the shade of a tree, which might be too low light of an environment for some orchids.
What kind of greenhouse shade cloth should you get? You want something with a rating of about 50% to 60% shade block, as more shade is probably too much for the more light loving orchids. You can buy it pre-cut and stitched, by the lineal foot in fix widths, which is likely cheaper. You can get shade cloth in greenhouse supply stores or home and garden stores. It is also easy to buy shade cloth on the internet. Greenhousemegastore.com and amazon.com are two sites on which you can purchase green house shade cloth.
Once you have your cloth, you can make your own cheap backyard greenhouse to grow your orchids. Here’s how. Get six milk crates and some kind of shelving. Two by fours will do just fine. Against a south facing wall in your yard (an area that gets morning sun but doesn’t get baked by the hot sun later in the day), arrange part of the shelving across two “pillars ”of milk crates consisting of two stacked crates each, to form the upper level of shelves for your orchids. Place the remaining two crates, one in front of each pillar of crates that you just made, and arrange more shelving across them. This forms the front shelf for your orchids. There you have it - a stepped planter on the cheap! Now you want to put up the shade cloth over your planter. You just need a way to suspend the top edge of the cloth above your shelves against the wall, which you could do by tying the top corners to something (like tree branches or wall hooks if available) using rope. The bottom end of the shade cloth will need to be leaned outwards, and you can keep it in place simply by weighing it down with bricks.
Place your orchids on the shelves, and make sure to water and fertilize as needed. (Water more in hot and dry weather - up to twice a week, less in colder or wetter conditions). This arrangement should be sufficient to reward you with healthy growth and blooms from many orchids