Patty Duke was dubbed by Gail Heiderman. Patty was not a great singer. She recorded her own versions of the doll songs on an LP and it's not very good.
Hayward was an okay vocalist. The only time her voice was used on a soundtrack was in the film I'll Cry Tomorrow. Hayward did NOT do her own singing in Valley of the Dolls. The dubber is big band vocalist, Margaret Whiting. It was later found that Whitings voice could not be used on the...
For Film Music Collectors - the song I'll plant My Own Tree was originally recorded by Garland, then Susan Hayward, then the dubber Margaret Whiting, then Eileen wilson for the soundtrack album. Does the DVD have good sounding versions of the Garland and Susan Hayward versions as extras ?