Plant pruned and planted in a song (7)
I believe the answer is:
dittany
'plant' is the definition.
(dittany is a kind of plant)
'pruned and planted in a song' is the wordplay.
'pruned' means to remove the last letter.
'planted in' indicates putting letters inside.
'a song' becomes 'ditty' (ditty is a kind of song).
'and' with its final letter taken away is 'an'.
'an' going within 'ditty' is 'DITTANY'.
(Other definitions for dittany that I've seen before include "oil-producer" , "Shrub" , "Aromatic plant" .)