The Collaborative International Dictionary of English v.0.48:

Gardener \Gar"den*er\, n.
   One who makes and tends a garden; a horticulturist.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gardener
    n 1: someone who takes care of a garden [syn: gardener,
         nurseryman]
    2: someone employed to work in a garden

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "gardener":
   boy, butler, chauffeur, coachman, driver, equerry, floriculturist,
   florist, fruit-grower, gentleman, gillie, horticulturist, houseboy,
   houseman, landscape architect, landscape gardener, landscapist,
   lord-in-waiting, man, manservant, market gardener, nurseryman,
   olericulturist, orchardist, orchardman, truck gardener, valet,
   valet de chambre, vigneron, vinegrower, viniculturist, vintager,
   viticulturist