Sitting in sun on the end of my outside garden (9)
I believe the answer is:
sedentary
'sitting' is the definition.
(thesaurus)
'sun on the end of my outside garden' is the wordplay.
'sun' becomes 'star' (the sun is a star).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'the end of' says to take the final letters.
'outside' means one lot of letters goes inside another (some letters go outside others).
'garden' becomes 'eden' (Garden of Eden in the Bible).
The last letter of 'my' is 'y'.
'star'+'y'='stary'
'stary' enclosing 'eden' is 'SEDENTARY'.
'in' acts as a link.
(Other definitions for sedentary that I've seen before include "inactive" , "not exercising one's talents?" , "Tending to spend too much seated and taking little exercise" , "Involving little or no energy" , "Sitting a lot and taking little exercise" .)