Decree persuades them to incorporate plants (8)
I believe the answer is:
creepers
'plants' is the definition.
(creeper is a type of plant)
'decree persuades them to incorporate' is the wordplay.
'to incorporate' indicates the answer is hidden within the clue (I've seen 'incorporates' mean this).
'CREEPERS' is hidden within 'decree persuades them'.
(Other definitions for creepers that I've seen before include "Plants, such as ivy" , "Soft-soled shoes" , "Plants growing along the ground" , "ramblers" , "Virginia and Ivy, say" .)