Established pansy regularly in garden (5)
I believe the answer is:
based
'established' is the definition.
('base' can be a synonym of 'establish')
'pansy regularly in garden' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'in' indicates putting letters inside.
'garden' becomes 'bed' (I've seen this in other clues).
The alternate letters of 'pansy' are 'as'.
'as' inserted inside 'bed' is 'BASED'.
(Other definitions for based that I've seen before include "Founded, grounded" , "Located" , "Established" , "Worthless" , "(Of aircraft) stationed" .)