The Collaborative International Dictionary of English v.0.48:

Horticultural \Hor`ti*cul"tur*al\, a. [Cf. F. horticultural.]
   Of or pertaining to horticulture, or the culture of gardens
   or orchards.
   [1913 Webster]

WordNet (r) 3.0 (2006):

horticultural
    adj 1: of or relating to the cultivation of plants

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "horticultural":
   arboricultural, blooming, bloomy, blossoming, efflorescent, floral,
   floreate, florescent, floriate, floriated, floricultural, florid,
   flowered, flowering, flowery, garden, hortulan, in bloom,
   in blossom, in flower, inflorescent, multiflorous, radiciflorous,
   rhizanthous, silvicultural, uniflorous, vinicultural,
   viticultural