Gentle exercise taken with a climber (5,3)
I believe the answer is:
sweet pea
'climber' is the definition.
(I've seen this before)
'gentle exercise taken with a' is the wordplay.
'gentle' becomes 'sweet' (I've seen this before).
'exercise' becomes 'pe' (Physical Education).
'taken with' is a charade indicator (letters next to each other).
'sweet'+'pe'+'a'='SWEET PEA'
(Other definitions for sweet pea that I've seen before include "Eat, weeps and gets climbing flowers" , "Fragrant flower" , "Climbing plant with fragrant flowers" , "Fragrant bloom" , "Highly-scented garden climber" .)