Vessel needing time on River Po (9)
I believe the answer is:
flowerpot
'vessel' is the definition.
(I know that flowerpot is a vessel)
'time on river po' is the wordplay.
'time' becomes 't' (abbreviation).
'on' says to put letters next to each other.
'river' becomes 'flower' (a river flows).
'flower'+'po'='flowerpo'
't' put after 'flowerpo' is 'FLOWERPOT'.
'needing' is the link.
(Other definitions for flowerpot that I've seen before include "What may hold" , "Something grows in this" , "Container for plants" , "Place for growing" , "spotted on window-sill" .)