Part of lab horticulturists hate (5)
I believe the answer is:
abhor
'hate' is the definition.
(abhorring is a kind of hating)
'part of lab horticulturists' is the wordplay.
'part of' indicates a hidden word.
'ABHOR' is hidden within 'lab horticulturists'.
(Other definitions for abhor that I've seen before include "Despise" , "Loathe, detest" , "Regard with disgust and hatred" , "Not like" , "Loathe, find repugnant" .)