Going north nowhere is open supplying coppice material (5)
I believe the answer is:
osier
'coppice material' is the definition.
(a coppice may be made up of osier trees)
'going north nowhere is open supplying' is the wordplay.
'going north' is a reversal indicator.
'supplying' indicates a hidden word.
'reiso' is hidden within 'nowhere is open'.
'reiso' back-to-front is 'OSIER'.
(Other definitions for osier that I've seen before include "Basket material" , "Weaving cane for Rosie" , "... source of twigs to make baskets" , "Flexible twig of a willow tree" , "Basket producer" .)