Flower produced by a set-up in Welsh town (8)
I believe the answer is:
'flower' is the definition.
(marigold is a kind of flower)
'a set-up in welsh town' is the wordplay.
'set-up' becomes 'rig' (I've seen this before).
'in' indicates putting letters inside.
'welsh town' becomes 'mold'.
'arig' inserted inside 'mold' is 'MARIGOLD'.
'produced by' acts as a link.
(Other definitions for marigold that I've seen before include "Garden plant of the daisy family", "Orange daisy", "Orange-flowered plant", "Yellow or orange flower", "Bright orange-yellow garden flower".)