"sjgarcia1958" <sjgarcia@...> writes:
> I seem to remember in the 70s using a layer of crushed charcoal
>(as in that used for aquarium filters) as a bottom layer, under the dirt.
>I don't recall why, though.
I've heard it's to keep it "sweet". I believe the activated charcoal will help
absorb bad chemicals in the system. Also, it'll provide surface area for
denitrifying
bacteria and some drainage so the soil isn't sitting in any pooled water.

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