Upset boozer? It's what nursery workers do (5)
I believe the answer is:
repot
'what nursery workers do' is the definition.
(move plants from one pot to another)
'upset boozer?' is the wordplay.
'upset' says the letters should be written backwards.
'boozer?' becomes 'toper' (boozer is a kind of toper).
'toper' in reverse letter order is 'REPOT'.
'it's' is the link.
(Other definitions for repot that I've seen before include "to fit into new container" , "Give room to expand" , "place somewhere new to put down roots" , "Move plant" , "transfer seedlings" .)