Green’s Dictionary of Slang

old or second-hand clothes hanging up for sale.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: wall flowers cloaths exposed to sale in Monmouth Street and other places.
1804		Sporting Mag. Jan. XXIII 220/2: A coat suspended on a peg in Monmouth-street, is called a wall flower.
1812		Spirit of Irish Wit 29: ‘His brother sold wall-flowers in Monmouth-street’.
1821		Flash Dict.
1835		G. Kent Modern Flash Dict.
1846		Swell’s Night Guide 135/1: Wall flowers, old clothes exposed for sale.
1859		Matsell Vocabulum.
1864, 1867, 1870		Hotten Sl. Dict.
1895		Crowe Aus. Sl. Dict. 93: Wall Flowers, second hand clothes hung up for sale.