(g hard). Get on, gardener! Get on, you slow and clumsy coachman. The allusion is to a man who is both gardener and coachman.
From you blue sky above us bent, The grand old gardener and his wife [Adam and Eve] Smile at the claims of long descent.
Lady Clara Vere de Vere
Thou, old Adam's likeness, Get to dress this garden.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894