Plant is hard to cultivate (6)
I believe the answer is:
radish
'plant' is the definition.
(radish plant is a kind of plant)
'is hard to cultivate' is the wordplay.
'to cultivate' is an anagram indicator (I've seen 'cultivated' mean this).
'is'+'hard'='ishard'
'ishard' is an anagram of 'RADISH'.
(Other definitions for radish that I've seen before include "Plant with crisp root eaten raw" , "Small red salad vegetable" , "Hard vegetable" , "Daikon or mooli" , "Pungent fleshy edible root eaten in salads" .)