Reportedly plant weed somewhere in London (4)
I believe the answer is:
soho
'somewhere in london' is the definition.
(area of London)
'reportedly plant weed' is the wordplay.
'reportedly' shows a homophone (sound like).
'plant' becomes 'sow'.
'weed' becomes 'ho' (I can't explain this - if you can you should give a lot more credence to this answer).
'sow' is a homophone of 'so'.
'so'+'ho'='SOHO'
(Other definitions for soho that I've seen before include "Once notorious part of central London" , "Nightclub area in London" , "Colourful London show-biz district" , "Call a large market for software" , "Colourful district in London's West End" .)