Nursery supply (5)
I believe the answer is:
mulch
'nursery supply' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mulch that I've seen before include "It holds moisture and checks weeds" , "It's laid around plants to retain moisture and keep down weeds" , "Requisite for garden" , "Ground cover" , "Garden additive" .)