Long grass totally pointless (4)
I believe the answer is:
'long' is the definition.
(to long or itch for something is to desire it)
I don't understand the remainder of the clue.
(Other definitions for itch that I've seen before include "Tickle; urge" , "A nagging desire" , "Constant desire" , "Tickling sensation of skin" , "source of irritation" .)