Landscape architect, unusually chastened, withdraws to be pragmatic (9)
I believe the answer is:
practical
'be pragmatic' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for practical that I've seen before include "Sensible" , "Pragmatic, hard-nosed" , "type of joker" , "Given to action rather than theory" , "Feasible; realistic" .)