Caster of shadow in garden? Little fellow therein cut one short (6)
I believe the answer is:
gnomon
'caster of shadow' is the definition.
(part of a sundial that casts a shadow)
I cannot understand how the remainder of the clue works.
(Other definitions for gnomon that I've seen before include "Sundial rod" , "Pointer on a sundial" , "Part of a sundial that casts the shadow" , "Part of a sundial projecting a shadow" , "where time casts its shadow" .)