Plant blossoming not certain (9)
I believe the answer is:
mayflower
'blossoming not certain' is the definition.
I can't judge whether this definition defines the answer.
'plant' is the wordplay.
I cannot quite see how this works, but
'plant' could be 'flower' (flower is a kind of plant) and 'flower' is present in the answer.
The remaining letters 'may' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mayflower that I've seen before include "Famous Pilgrim ship" , "Pilgrim Fathers' vessel" , "Pilgrims' vessel" , "Pilgrims Fathers' ship" , "Pilgrim Fathers' ship to the US" .)