Gardening accessory that's old hat (6)
I believe the answer is:
cloche
'old hat' is the definition.
(old-fashioned type of hat)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cloche that I've seen before include "Woman's helmet-like hat" , "Cover for garden plants" , "seedlings may need it" , "protection for young stock?" , "useful in the garden" .)