Herb old miners planted outside Baltic port (8)
I believe the answer is:
origanum
'herb' is the definition.
(origanum is a kind of herb)
'old miners planted outside baltic port' is the wordplay.
'old' becomes 'o' (abbreviation).
'miners' becomes 'NUM' (National Union of Mineworkers).
'planted outside' indicates putting letters inside.
'baltic port' becomes 'riga' (capital of Latvia, a Baltic nation).
'o'+'num'='onum'
'onum' placed around 'riga' is 'ORIGANUM'.
(Other definitions for origanum that I've seen before include "Herb of marjoram genus" , "Wild herb" , "aromatic plant" .)