Knotted tape useful to gardeners (4)

I believe the answer is:

peat

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'useful to gardeners' is the definition.
I can't tell whether this definition defines the answer.

'knotted tape' is the wordplay.
'knotted' indicates an anagram.
'tape' is an anagram of 'PEAT'.

Can you help me to learn more?

(Other definitions for peat that I've seen before include "Organic fuel" , "Saturated and compressed vegetable matter, used as fuel when dried out" , "Fuel from bogs" , "Dried plant material used as fuel" , "Bog material" .)

I've seen this clue in the Evening Standard.

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