Form of tape useful in the garden (4)

I believe the answer is:

peat

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'form' is the definition.
(I have seen 'Form of fuel ' mean 'peat' so perhaps 'form' could also mean 'peat')

'tape useful in the garden' is the wordplay.
'tape' anagrams to 'PEAT'.
However, I am unsure how the anagram is indicated.

'of' acts as a link.

Can you help me to learn more?

(Other definitions for peat that I've seen before include "Fuel from bogs" , "Vegetable matter in bogs, like turf" , "Vegetable deposit used as fuel and fertiliser" , "Fuel or compost (but no longer to be used as such!)" , "Tape around turf" .)

I've seen this clue in the Evening Standard.

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