Grow a pair of primarily nice-scented Umbellularia in plot (3,2)

'grow a pair' is the definition.
(both can be used to tell someone to be braver)

'primarily nice-scented umbellularia in plot' is the wordplay.
'primarily nice scented umbellularia' becomes 'nu' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'plot' becomes 'map' (synonyms).
'nu' inserted inside 'map' is 'MAN UP'.

'of' acts as a link.