Planted geraniums around border (4)
I believe the answer is:
edge
'border' is the definition.
(I know that border can be written as edge)
'planted geraniums around' is the wordplay.
'around' says the answer is hidden in the clue.
'EDGE' is hidden within 'planted geraniums'.
(Other definitions for edge that I've seen before include "Keenness" , "Cutting side as of knife, or margin" , "marginal advantage" , "Guitarist with U2" , "Some bordering" .)