Staunch supporter of Kew Gardens? (4)
I believe the answer is:
stem
This might be a double definition.
'staunch' is the first definition.
(I know that staunch can be written as stem)
'supporter of kew gardens?' is the second definition.
'stem' can be an answer for 'supporter' (I've seen this before). I'm unsure of the 'of kew gardens?' bit.
Can you help me to learn more?
(Other definitions for stem that I've seen before include "Hold back - stock - check" , "Stop; stalk; ship's timber" , "Main stalk of a plant" , "Slender upright part of wine glass" , "something growing?" .)