Cicca, a great number of the orchids you see are Air Orchids. They are called epiphytes, meaning that they do not need soil to grow...like some bromeliads and some mosses. The group of orchids that require soil are called Terrestrial Orchids or Ground Orchids. Since most orchids are cold sensitive, growing them in containers with bark and moss is the best way to move them into a warmer place for winter. You would need to match their light requirements to have them on your patio, as most of them do not do well in full sun...they tend to attach themselves to trees for support. They are not parasitic at all and do not harm the host plant.