Go too far, having finished with new growth (9)
I believe the answer is:
overshoot
'go too far' is the definition.
(to overshoot is to go past)
'finished with new growth' is the wordplay.
'finished' becomes 'over' (over can mean finished or ended).
'with' is a charade indicator (letters next to each other).
'new growth' becomes 'shoot' (a shoot is new growth from a plant).
'over'+'shoot'='OVERSHOOT'
'having' acts as a link.
(Other definitions for overshoot that I've seen before include "Go past unintentionally" , "Go extra distance" , "Go beyond the mark" , "Go past the mark" , "fail to stop where intended" .)