Abstract: Garden window sub frame members for inclusion in a garden window frame assembly are disclosed. The garden window sub frame members include a section with sufficient width to at least partially cover an existing window frame in a replacement application, or pocket in masonry or other flush opening. The garden window sub frame members include provision for easily attaching a variety of interior trim sections to accommodate various finish applications. The garden window sub frame members include a channel shaped to accept a flange insert to allow multiple means of attaching the garden window to a structure. The flange insert includes an extension disposed perpendicular to the flange that may also be used to attach the frame member to the structure or provide an exterior finish, or both.