It grows in the south of Ireland (3)
I believe the answer is:
fir
'it grows' is the definition.
The definition suggests a singular noun which matches the answer.
'in the south of ireland' is the wordplay.
'in the south' says to take the final letters (I've seen 'in the south of' mean this (in a down clue, the bottom letter)).
'ireland' becomes 'ir' (abbreviation for Ireland).
The final letter of 'of' is 'f'.
'f'+'ir'='FIR'
Can you help me to learn more?
(Other definitions for fir that I've seen before include "Tree for an Irishman" , "Conifer tree" , "Evergreen tree for Gaelic men" , "Pine tree for Gaelic men?" , "Coniferous tree" .)