What garden centres sell? There's fuss over British Standards (8)

'what garden centres sell?' is the definition.
(I know that many garden centres sell potherbs)

'fuss over british standards' is the wordplay.
'fuss' becomes 'pother' (pothering is a kind of fussing).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'british standards' becomes 'BS' (abbreviation).
'pother'+'bs'='POTHERBS'

'there's' is the link.