"Rupert" wrote
I recently read that Kew recommend planting trees in square holes and
adding no nutrients, which seems to go against what I have always
believed.

The square hole is thought to help the roots break out of their circular
path (as when in a pot), they grow out and hit a sharp corner then have to
start entering the soil instead of continuing to go round and round as if
still in a pot. That's the current theory.

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Regards
Bob
In Runnymede, 17 miles West of London