Lawn growth (4)
'lawn growth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for grass that I've seen before include "Reefer's content" , "Pasturage" , "blow the gaff" , "something in the park?" , "Weed" .)
(Other definitions for moss that I've seen before include "English racing driver, b. 1929" , "Plant reproducing by spores" , "What's not found on a rolling stone" , "Veteran racing driver" , "Spore-bearing plant; bog" .)