Garden style is supreme and surprisingly airy (7)
I believe the answer is:
topiary
'garden style' is the definition.
(topiary is shaping shrubs or bushes)
'supreme and surprisingly airy' is the wordplay.
'supreme' becomes 'top' (the supreme or best).
'and' is a charade indicator (letters next to each other).
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'airy' is an anagram of 'iary'.
'top'+'iary'='TOPIARY'
'is' acts as a link.
(Other definitions for topiary that I've seen before include "Gardening skill" , "Art of clipping shrubs into ornamental shapes" , "I pray to find ornamental shrub clipping" , "fancy hedging?" , "Clipping trees to shape" .)