Four years establishing climbing plant (3)
I believe the answer is:
ivy
'climbing plant' is the definition.
(ivy is a type of climbing plant)
'four years' is the wordplay.
'four' becomes 'IV' (Roman numerals).
'years' becomes 'y' (abbreviation).
'iv'+'y'='IVY'
'establishing' acts as a link.
(Other definitions for ivy that I've seen before include "Four-year" , "Poisonous plant" , "woman" , "Vine with evergreen leaves" , "Bush" .)