Cleaning occasionally, odours can start to grow (7)
I believe the answer is:
dusting
'cleaning' is the definition.
(dusting is a kind of cleaning)
'occasionally odours can start to grow' is the wordplay.
'occasionally' indicates alternate letters.
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'start to' suggests taking the first letters.
The first letter of 'grow' is 'g'.
The alternate letters of 'odours' are 'dus'.
'dus'+'tin'+'g'='DUSTING'
(Other definitions for dusting that I've seen before include "Cleaning" , "Light covering; a home chore" , "light cover" .)