Trimming fruit mostly during start of growth (7)
I believe the answer is:
pruning
'trimming' is the definition.
(I know that pruning is a type of trimming)
'fruit mostly during start of growth' is the wordplay.
'fruit' becomes 'prune' (prune is a kind of fruit).
'mostly' means to remove the last letter.
'during' becomes 'in' (e.g. during February means in February).
'start of growth' becomes 'g' (I am not sure about this - if you are sure you should believe this answer much more).
'prune' with its last letter removed is 'prun'.
'prun'+'in'+'g'='PRUNING'
Can you help me to learn more?
(Another definition for pruning that I've seen is " Trimming (trees)".)