Flower fertiliser (6)
I believe the answer is:
pollen
This clue could be a double definition.
'flower' is the first definition.
The answer and definition can be both plants as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'fertiliser' is the second definition.
(pollen fertilises plants)
Can you help me to learn more?
(Other definitions for pollen that I've seen before include "Fine powder discharged from a plant" , "What sticks to insects" , "Fertilising dust from flower" , "Flower powder" , "Fertilising grains" .)