No iris develops without good roots (7)
I believe the answer is:
origins
'roots' is the definition.
('origin' can be a synonym of 'root')
'no iris develops without good' is the wordplay.
'develops' is an anagram indicator.
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'good' becomes 'g' (abbreviation).
'no'+'iris'='noiris'
'noiris' is an anagram of 'oriins'.
'oriins' enclosing 'g' is 'ORIGINS'.
(Other definitions for origins that I've seen before include "'Beginnings, starting points (7)'" , "Beginnings, sources" , "So I grin (anag.)" , "Pedigree" , "Where things begin" .)