Jelly available in tea garden (4)
I believe the answer is:
agar
'jelly' is the definition.
(gelatinous substance)
'available in tea garden' is the wordplay.
'available in' indicates a hidden word.
'AGAR' is hidden in the letters of 'tea garden'.
(Other definitions for agar that I've seen before include "used in making soups?" , "Food thickening agent obtained from seaweed" , "Jelly got from seaweeds, used in foods" , "Gelatinous substance from seaweed used as a thickener in foods." , "Substance derived from seaweed" .)