Heartily ate without shelter in garden perhaps (6)
I believe the answer is:
noshed
'heartily ate' is the definition.
'noshed' can be an answer for 'ate' (noshing is a kind of eating). I am not sure about the 'heartily' bit.
'without shelter in garden perhaps' is the wordplay.
I cannot really see how this works, but
'without' could be 'no' and 'no' is found within the answer.
'shelter' could be 'shed' (I've seen this before) and 'shed' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for noshed that I've seen before include "tucked in" , "Put away" , "Ate - hens do (anag)" , "had food" .)