Before planting an orchid on a tree, you need to know about one critical distinction. There are two main types of orchids, terrestrial orchids, and epiphytic orchids. Terrestrial orchids are like most other plants in that they root in the ground and gain their moisture and nutrients from the soil. Epiphytic orchids, like the popular phalaenopsis orchids, are air plants that don't need soil and instead thrive by attaching to trees.