Tillandsias are commonly known as air plants because they are not planted in soil. In the wild they cling to trees and rocks with their roots whose sole purpose is to secure the plant. Moisture and nutrients are absorbed through the leaves. As a result caring for these air plants is somewhat different from other plants grown in soil. The three essentials that they need are air, water and light. This article by Stephanie Rose on the Garden Therapy website tells you how to care for these unusual plants.
You can read her article at Garden Therapy
Image source: Crissty