I have always thought that the bracha בורא עשבי בשמים is limited to fragrant "herbs" that are used in cooking and perfumes. Thus, you would say it on smelling parsley, sage, rosemary and thyme (and, maybe while listening to "Scarborough Fair", as well.) and similar herbs.
But the term עשב means "grass". Would you say it if you smell grass (esp. when freshly mown)? What about on the grasses emanating from root vegetables such as carrots and turnips?