Horticulturalist’s fantastic red range (8)
I believe the answer is:
gardener
'horticulturalist's' is the definition.
(horticulture is gardening)
'fantastic red range' is the wordplay.
'fantastic' indicates an anagram.
'red'+'range'='redrange'
'redrange' is an anagram of 'GARDENER'.
(Other definitions for gardener that I've seen before include "Horticulturist" , "One growing plants" , "Tender of plants" , "Cultivator" , "Red anger of an outdoor worker" .)