Greenhouse Blues was originally an instrumental track which was a mainstay of The Forefathers' live set.  (The Forefathers are Rich's "other" band - check 'em out)  The Forefathers never got around to recording Greenhouse Blues, so ZFB got to pick it up and made something rockin' and markedly more aggressive than it had been previously.  GHB features the guys on bass, harmonica and guitar solos and has a roots-rock vibe to it.  After the main recording was complete, Steve noticed that the lyrics really had nothing to do with the title of the song, so a quickie intro was concocted and recorded, which contains the only reference to the titular subject matter.