White dog behind a plant (9)
I believe the answer is:
alabaster
'white' is the definition.
(alabaster is a kind of white)
'dog behind a plant' is the wordplay.
'dog' becomes 'lab' (short for labrador).
'behind' means one lot of letters go next to another.
'plant' becomes 'aster' (aster is a kind of plant).
'lab' after 'a' is 'alab'.
'alab'+'aster'='ALABASTER'
(Other definitions for alabaster that I've seen before include "medium of sculpture" , "Arabs tale (anag.)" , "Sort of gypsum" , "White mineral used for carving" , "White substance" .)