Whether it be grass, flowers or leaves - the shops are literally taking a leaf out of natures book and are using them in their displays! The three images below are from Heals. I think the palm leaf image is the most striking and I think if they had followed up that close up, fill the whole backdrop effect with the orchid flowers and maybe sand in the third backdrop then the three room sets would have been more cohesive.
Palm trees and leaves were actually a very popular choice for loads of retailers including Dune...
..Accessorize...
..and the rest!
Flowers have been used here to fill the spaces above the main window displays:
Grass has been used at The White Company and Jack Wills to contain and focus the floor based displays: