Old beast of burden climbing to get aromatic plant (7)
I believe the answer is:
oregano
'aromatic plant' is the definition.
(I know that oregano is a type of spice)
'old beast of burden climbing' is the wordplay.
'old' becomes 'o' (abbreviation).
'beast of burden climbing' becomes 'regano' (I am not sure about this - if you are sure you should believe this answer much more).
'o'+'regano'='OREGANO'
'to get' acts as a link.
Can you help me to learn more?
(Other definitions for oregano that I've seen before include "that's aromatic" , "Pizza herb" , "Mediterranean herb" , "Herb - a no-goer (anag)" , "part of Mediterranean diet?" .)