Spanish Moss, or more accurately, Tillandsia usneoides, is indeed an icon of the South here in the United States, and is also one of our native bromeliads. In fact, the genus is represented by a number of species that are native here. My focus in this article, though is this plant that is not a moss, nor is it even distantly related to mosses.
T. usneoides has a specific name that means "like Usnea", which is a reference to the lichen genus Usnea, the Beard Lichen (see photo, below left). A casual observer might mistake a growth of Usnea for a young patch of Spanish Moss, but a closer inspection would reveal that the two species are only faintly similar. Usnea can be found growing throughout the world, while Spanish Moss is only found naturally in the southeastern United States, from Texas to Florida, and in Central and South America. Trees hosting colonies of Spanish Moss look like they possess multiple thick gray beards on their branches. When moistened, these live plants can be seen to have a greenish look, which betrays their nature as photosynthetic plants and not hair!
Growing your own!
If you want to try growing this plant, you don't need a pot or soil mix. You just need a bright or sunny place outdoors to hang pieces of it, and you also need high relative humidity. This plant grows epiphytically on trees or other supports, and derives all the water and nutrients it requires from dew, rain, or other ambient moisture. This is why you are not likely to find Spanish Moss in the desert southwest or in California. I don't see very much Spanish Moss wild around south Florida, but some people do "plant" it deliberately in trees for the Southern or Gothic ambiance that it provides. When grown in this way, an occasional spray with water, especially during the drier parts of the year, will help keep the plant happy. Where I live, a few other native Tillandsia species have sprung up naturally on tree limbs here and there, so I decided to add some Spanish Moss to the mix as well. T. usneoides grow from either pieces scattered by birds and other animals, or from the small seeds that are produced by mature plants of the species.
This plant has a reputation for harboring chiggers, but this is only true when the plants fall off the trees and come into contact with the ground. There, the chiggers can climb on and wait for the hapless passersby, promising them an itch to scratch if their bare skin comes into contact with the fallen T. usneoides. Some animals do find this plant to be a hospitable place to live, including bats, lizards, snakes and even a spider that is found nowhere else but in association with Spanish Moss.
The decline in abundance of Spanish Moss is one change that can be related to human activity. The evidence indicates that acid rain resulting from air pollution is toxic to the plant. So while you might still find plenty of T. usneoides growing in rural areas, the big cities with plenty of pollution are going to host little or no colonies of it. In this way, Usnea and Spanish Moss are similar, in that they both react negatively to the presence of pollutants in the air. In this manner they can serve the same function as the "canary in the coal mine". So if your environment is in every way conducive to the growth of Spanish Moss and you can't seem to get it to grow, pollution in your area may be the reason.
Image credit: Public Domain and GNU Free Documentation License