The 'Garden' once so fruitful (6)
I believe the answer is:
covent
'garden once so fruitful' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'the' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
The remaining letters 'coven' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for covent that I've seen before include "--- Garden, opera house" , ". . . . . . Garden is London opera district" .)