It is hard to vary salad food (6)
I believe the answer is:
radish
'food' is the definition.
(radish is a kind of food)
'it is hard to vary salad' is the wordplay.
'is hard' can be anagrammed to 'RADISH'.
But, I am not sure how this is indicated.
Can you help me to learn more?
(Other definitions for radish that I've seen before include "Hottish salad plant" , "Root eaten raw in salads" , "Pungent fleshy edible root eaten in salads" , "Small red salad vegetable" , "Root vegetable used in salads" .)