Wrongly cultivating only rose and rue (11)
I believe the answer is:
erroneously
'wrongly' is the definition.
(I've seen this before)
'cultivating only rose and rue' is the wordplay.
'cultivating' indicates an anagram.
'and' says to put letters next to each other.
'only'+'rose'='onlyrose'
'onlyrose' after 'rue' is 'rueonlyrose'.
'rueonlyrose' with letters rearranged gives 'ERRONEOUSLY'.
(Other definitions for erroneously that I've seen before include "Mistakenly" , "Wrongly" , "in a wrongful manner" , "In an incorrect manner" .)