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I don't want the outer edges to always be dry but I do concentrate around the root when I water.
2 gallons is good.
Poke with your finger and let the top centimetre get dry before watering again.

Don't water more than the soil has time to get dry again in 2-3 days.
Just off the top of my head, I would imagine you use about a quarter as much water as soil.
Something like that.

At least, thats my 2 cents.

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