Engineer in lab coat dealing with plants (9)
I believe the answer is:
botanical
'dealing with plants' is the definition.
'engineer in lab coat' is the wordplay.
'engineer' indicates an anagram.
'in'+'lab'+'coat'='inlabcoat'
'inlabcoat' anagrammed gives 'BOTANICAL'.
(Other definitions for botanical that I've seen before include "Description of some gardens" , "Relating to the study of plants" , "(Gardens) of scientific interest" .)