Small gardens can be asymmetrical (4)
I believe the answer is:
skew
'be 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'
'can' is the link.
(Other definitions for skew that I've seen before include "Place obliquely" , "Misrepresent" , "Oblique, make crooked" , "Aslant, bias" , "Turn aslant" .)