Salad ingredient, possibly, is hard (6)
I believe the answer is:
radish
'salad ingredient' is the definition.
(radishes are often used in salads)
'possibly is hard' is the wordplay.
'possibly' indicates an anagram.
'is'+'hard'='ishard'
'ishard' with letters rearranged gives 'RADISH'.
(Other definitions for radish that I've seen before include "Pungent fleshy edible root eaten in salads" , "Bit of salad" , "Root eaten raw in salads" , "Pungent, red salad vegetable" , "3 down" .)