Lawyer to call, wanting old plant (6)
I believe the answer is:
daphne
'old plant' is the definition.
'daphne' can be an answer for 'plant'. I am unsure of the 'old' bit.
'lawyer to call' is the wordplay.
'lawyer' becomes 'da' (D.A. is an example).
'to call' becomes 'phne' (I can't explain this - if you can you should believe this answer much more).
'da'+'phne'='DAPHNE'
'wanting' is the link.
(Other definitions for daphne that I've seen before include "Evergreen shrub" , "Shrub - girl's name" , "Name of girl or shrub" , "He'd nap around this shiny shrub" , "Had pen of the shiny shrub" .)