One put to bed happened to have a bad back (8)
I believe the answer is:
camellia
'one put to bed' is the definition.
(plant which may put in a flower bed)
'happened to have a bad back' is the wordplay.
'happened' becomes 'came' (to happen upon and to come upon mean to encounter).
'to have' says to put letters next to each other.
'bad' becomes 'ill' (similar in meaning).
'back' is a reversal indicator.
'a'+'ill'='aill'
'aill' written backwards gives 'llia'.
'came'+'llia'='CAMELLIA'
(Other definitions for camellia that I've seen before include "Flowering plant related to tea" , "Email Cal about the flowering shrub" , "Showy shrub, rel. to tea" , "Japonica" , "Claim ale from the flowering shrub" .)