Elder's after nook for ornamental garden feature (3,4)
I believe the answer is:
bay tree
'ornamental garden feature' is the definition.
(bay trees may be used as ornamental plants)
'elder's after nook' is the wordplay.
'elder' becomes 'tree' (elder is a type of tree).
'after' says to put letters next to each other.
'nook' becomes 'bay' (bay can mean an architectural nook or alcove).
'tree' put after 'bay' is 'BAY TREE'.
'for' is the link.
(Other definitions for bay tree that I've seen before include "Mediterranean shrub" , "Laurel" , "Supplier of berries" , "An evergreen" .)