Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow . If you have lichens growing on in your yard, be delighted. They’re considered indicators of healthy air. They lack roots and get their carbon dioxide, water and all nutrients, except the carbohydrates the algal partner manufactures, from the surrounding atmosphere. As a result, air-borne pollutants become concentrated in them. The Forest Service has a program called the National Lichens and Air Quality Data Base to