Scheme of a garden bed (4)
I believe the answer is:
plot
This clue is a triple definition!
'scheme' is the first definition.
(I know that plot is a type of scheme)
'of' is a link.
'a garden' is the second definition.
(I've seen this before)
'bed' is the third definition.
(a bed or plot of soil)
(Other definitions for plot that I've seen before include "Graph; piece of ground" , "Mark position" , "Machination" , "See 12 Across" , "Piece of ground - conspiracy" .)