An orchid tree is a variation on mounting orchids, except you're putting many orchids on a branch or branches to give it a completely natural look. The concept can be used in those areas of the country where orchids can be grown outdoors most of the year, but must be protected from a few frosts during the winter months; or if you are lucky enough to have a large enough greenhouse, brought inside during the colder winter months. It would also work wonderfully under lights in an alcove or under stairs area that proves to be a difficult place to decorate.
To start out, you must select the base for your tree, or build a wire mesh and cover it with cork. Remember that if you're going to be moving the structure it cannot be too heavy. And you will need to make sure that it will not topple over when planted. Generally a tripod arrangement will ensure enough stability.
Attach the larger plants to the bottom for aesthetic reasons and the smallest on the upper portions. Think of the size of the branches on a tree, the largest are at the bottom and the smallest at the top. This will also provide extra weight at the bottom to balance the weight of the structure.
When choosing plants, be sure to try to pick out plants that will require similar light, temperature and humidity conditions. Depending on how you place your orchid tree, some will obviously get more light than others. Be aware of this when you start arranging the plants you wish to mount. Another factor to consider is flowering times. Do you want all your plants flowering at the same time, or several flowering at the same time throughout the year? And of course, the most fun of all, how are you going to arrange the different colors on the tree?
If possible soak the structure overnight before adding plants, otherwise wet it thoroughly with a hose. Take your plants from their pots, clip off any dead or brown roots and clean up the plants by removing dead sheaths, and back bulbs. Position the plants around the tree and if you want tie them on with a string until you're satisfied with the arrangement. Then mount as you would any orchid on a mount with sphagnum moss attached with fishing wire against the structure. Then tie on your plant being careful not to cut into the pseudobulbs or roots. I prefer putting a bit of sphagnum on top of the roots too to provide extra moisture to the plants during hot periods. Continue mounting until all your plants are situated as you want them.
Mist thoroughly and place in a humid shaded area for two weeks to a month in order to allow the plants to accustom themselves to their new home. Mist every other day and water as you would any other mounted plant. Gradually move into a sunnier area over the course of about a week as you would for any other orchid.