Went on to add a grass border (7)
I believe the answer is:
resumed
'went on' is the definition.
(resuming is a kind of going on)
'add a grass border' is the wordplay.
I cannot quite see how this works, but
'add' could be 'sum' (synonyms) and 'sum' is found within the answer.
'grass' could be 'reed' (type of grass plant) and 'reed' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for resumed that I've seen before include "Recommenced" , "Carried on again" , "Took up again" , "Started again where one had left off" , "Restarted" .)