Decorated his garden, somehow (9)
I believe the answer is:
garnished
'decorated' is the definition.
(garnishing is a kind of decorating)
'his garden somehow' is the wordplay.
'somehow' is an anagram indicator.
'his'+'garden'='hisgarden'
'hisgarden' with letters rearranged gives 'GARNISHED'.
(Other definitions for garnished that I've seen before include "Decorated" , "Added parsley, perhaps" .)