Garden ably designed, for the most part (2,3,5)
I believe the answer is:
by and large
'for the most part' is the definition.
(I've seen this before)
'garden ably designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'garden'+'ably'='gardenably'
'gardenably' is an anagram of 'BY AND LARGE'.
(Other definitions for by and large that I've seen before include "Speaking generally" , "All things considered" , "In the main" , "In general" , "On the whole" .)