Hesitation in unsteady part of garden (7)
I believe the answer is:
rockery
'part of garden' is the definition.
(I've seen this before)
'hesitation in unsteady' is the wordplay.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'in' means one lot of letters goes inside another.
'unsteady' becomes 'rocky' (I've seen this before).
'er' put inside 'rocky' is 'ROCKERY'.
(Other definitions for rockery that I've seen before include "Garden alpine area" , "Part of garden" , "Garden feature with alpines" .)