Spooner's magical method to remove unwanted plants such as this? (9)
I believe the answer is:
speedwell
'spooner's magical method to remove unwanted plants such as this?' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
(Other definitions for speedwell that I've seen before include "Flowering plant" , "Small creeping herbaceous plant with blue or pink flowers" , "Small plant, veronica" , "Small blue flower of the genus veronica" , "bloomer?" .)