Kitty has spread fertiliser (6)
I believe the answer is:
potash
'fertiliser' is the definition.
(I know that potash is a type of fertiliser)
'kitty has spread' is the wordplay.
'kitty' becomes 'pot' (both can mean a shared fund).
'spread' indicates an anagram.
'has' with letters rearranged gives 'ash'.
'pot'+'ash'='POTASH'
(Other definitions for potash that I've seen before include "Potassium carbonate or hydroxide" , "Potassium compound used as fertiliser" , "field dressing" , "Pathos (anag)" , "Type of fertiliser" .)