Lay down the lawn (3)
I believe the answer is:
sod
'lay down the lawn' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sod that I've seen before include "A lulmp of turf" , "'Sward, turf (3)'" , "Piece of peat or grass" , "Lump of earth" , "A piece of sward." .)