Prepared drainage for shrub (8)
I believe the answer is:
gardenia
'shrub' is the definition.
(gardenia is a kind of shrub)
'prepared drainage' is the wordplay.
'prepared' indicates anagramming the letters.
'drainage' with letters rearranged gives 'GARDENIA'.
'for' is the link.
(Other definitions for gardenia that I've seen before include "Drainage for shrub with white or yellow flowers" , "A reading (anag.)" , "Waxlike flower" , "bloomer!" , "Fragrant shrub, red again (anag.)" .)