Part of flower, first planted in raised border (6)
I believe the answer is:
pistil
'part of flower' is the definition.
(I know this)
'first planted in raised border' is the wordplay.
'first' becomes 'ist' (ist resembles lst).
'planted in' means one lot of letters goes inside another.
'raised' shows that the letters should be reversed in order (going up in a down clue).
'border' becomes 'lip' (I've seen this in other clues).
'lip' back-to-front is 'pil'.
'ist' placed into 'pil' is 'PISTIL'.
(Other definitions for pistil that I've seen before include "Seed-producing part of a flower" , "Female part of a plant" , "This part of a flower sounds like a gun" , "Style in flower" , "Female organ of a flower" .)