Grow former plant and next derivative initially (6)
I believe the answer is:
expand
'grow' is the definition.
(expanding is a kind of growing)
'former plant and next derivative initially' is the wordplay.
'former' becomes 'ex'.
'initially' says to take the initial letters.
The first letters of 'plant and next derivative' is 'pand'.
'ex'+'pand'='EXPAND'
(Other definitions for expand that I've seen before include "Fill out" , "Amplify" , "Walk through water" , "produce growth" , "Become larger or more extensive" .)