Grows, once one looks after (7)
I believe the answer is:
extends
'grows' is the definition.
(extending is a kind of growing)
'once one looks after' is the wordplay.
'once' becomes 'ex'.
'one looks after' becomes 'tends' (I've seen this before).
'ex'+'tends'='EXTENDS'
(Other definitions for extends that I've seen before include "Makes longer" , "Enlarges" , "holds out" , "Lengthens" , "Reaches or stretches out, say the hand of friendship" .)