Flog close-grained wood (5)
I believe the answer is:
birch
I believe this clue is a double definition.
'flog' is the first definition.
(birching is a kind of flogging)
'close-grained wood' is the second definition.
(wood from a birch tree)
(Other definitions for birch that I've seen before include "to beat the rest?" , "Hardy tree" , "'Slender tree, the bark could be silver (5)'" , "Flog" , "Tree bearing catkins" .)