Castles in the air made yards impracticable (9)

I believe the answer is:

daydreams

I'm a little stuck... Click here to teach me more about this clue!

'castles in the air' is the definition.
(I've seen this in another clue)

'made yards impracticable' is the wordplay.
'made yards' anagrams to 'DAYDREAMS'.
But, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for daydreams that I've seen before include "Idly imagines" , "hopeful aspirations?" , "Reveries" , "Fantasise while awake" .)

I've seen this clue in the Sydney Morning Herald.

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