From Lost Fables Wiki
Grove's Sighs are the whispers of nature itself, captured through crude means to be useful to hands less graceful than those of a Spring Elf's. While they merely sound like the creaking of bark to any other race, a Spring Elf can usually hear a single phrase in the long, steady language of the trees.
Requiring an alchemical windscarf made of mystic hemp, with a specially constructed device which looks much like a dreamcatcher at the mouth. Note that this is a specific type of alchemical windscarf, made for this particular purpose. The tail of this windscarf must trail off into a container of some sort, which must be held upright. If the container is sealed away from the wind, the sigh is lost. The catcher must be set up within 100 meters of at least 15 trees. One can only gather a single sigh per age with a setup like this.
Grove's Sighs are good for making all sorts of things grow when applied directly to a plant, doubling its rate of growth. By adding other things to Grove’s Sighs and then the mixture to plants, all sorts of odd and magical plants can be grown.