"Deck the Halls" plant (5)
I believe the answer is:
holly
'deck the halls plant' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for holly that I've seen before include "Evergreen tree associated with Christmas" , "Girl" , "Prickly shrub" , "Prickly tree" , "It has red berries and glossy leaves with prickles" .)