Vegan at first madly ardent to be green (7)
I believe the answer is:
verdant
'be green' is the definition.
(I've seen this before)
'vegan at first madly ardent' is the wordplay.
'at first' suggests taking the first letters.
'madly' is an anagram indicator.
The initial letter of 'vegan' is 'v'.
'ardent' is an anagram of 'erdant'.
'v'+'erdant'='VERDANT'
'to' is the link.
(Other definitions for verdant that I've seen before include "Leafy" , "Green like grass or fields" , "Having green growth" , "Unsophisticated" , "Rather green" .)