Tillandsia usneoides is more commonly known as Spanish Moss. In the deep South, it grows in streamers from trees, most commonly Live Oaks and Bald Cypress in shaded, high humidity environs. It is a true epiphyte, a plant that lives upon other plants; from Greek "epi"=upon "phyte"=plant.
So, why do we have Spanish Moss for sale? Well, the tiny green and yellow flowers are nice. For truly for the general ambiance it adds to our cool, moist greenhouse - and for the contribution it makes toward keeping the air humid for our Masdevallias. We just like it.
So, how do you grow Spanish Moss? Hang it in your greenhouse or patio in shade to part shade, water it at least three times a week in dry weather, and divide it as it increases. We spritz ours with dilute fertilizer when we water the orchids, and they respond by growing faster with increased blooming. I consider this an easy plant to grow in appropriate conditions. It does not like dry air, and please take that into account before you purchase this little gem.
We pack this by the pound. A quarter pound is a ball about the size of a soccer ball, or about a four foot streamer. In good conditions it will double in size every year.