Container for plant covering large part of garden (4)
I believe the answer is:
plot
'part of garden' is the definition.
(plot of land)
'container for plant covering large' is the wordplay.
'container for plant' becomes 'pot'.
'covering' means one lot of letters goes inside another.
'large' becomes 'L' (eg in clothes sizes).
'pot' placed around 'l' is 'PLOT'.
(Other definitions for plot that I've seen before include "Machination" , "Vegetable garden - scheme" , "Novel story - secret plan" , "Film story; graph" , "Design" .)