The tree I myself planted outside the club (6)
I believe the answer is:
mashie
'the club' is the definition.
(mashie is a kind of club)
'the tree i myself planted outside' is the wordplay.
'the tree' becomes 'ash' (ash is a kind of tree).
'myself' becomes 'me'.
'planted outside' indicates putting letters inside.
'ash'+'i'='ashi'
'ashi' placed within 'me' is 'MASHIE'.
(Other definitions for mashie that I've seen before include "Old golf club" , "Golf club for lofting" , "Old-fashioned golf club" , "One of 9 [CLUBS]" , "He aims (anag) - golfer's five iron, formerly" .)