Bag carried by gardeners at Chelsea (7)
I believe the answer is:
satchel
'bag' is the definition.
(I've seen this before)
'carried by gardeners at chelsea' is the wordplay.
'carried by' says the answer is hidden in the clue.
'SATCHEL' is hidden in the letters of 'gardeners at chelsea'.
(Other definitions for satchel that I've seen before include "Bag -- latches (anag)" , "Schoolchild's carrier" , "Get school item" , "Bag for school books" , "Small case with a shoulder strap" .)