Small gardens may be asymmetrical (4)
I believe the answer is:
skew
'asymmetrical' is the definition.
(thesaurus)
'small gardens' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'gardens' becomes 'kew' (Kew Gardens in London).
's'+'kew'='SKEW'
'may be' is the link.
(Other definitions for skew that I've seen before include "Turn aslant" , "Not symmetrical" , "Colour" , "Slant, bias" , "Oblique, make crooked" .)