This is more of a hypothetical question. If someone is using 1/4 particle size of 25% pine bark, 25% DE, 25% Pumice and 25% Lava, is it possible to overwater? In traditional soil, I assume trees become over watered because of a lack of air. So in a free draining soil is it impossible to over water a tree since oxygen will be available? Thanks everyone!
I use this mix precisely for most of my trees (except I use Fir bark instead of Pine bark). I adjust components a bit accordingly, but I start with 1:1:1:1 of pumice, lava, DE (Napa 8822), and fir bark (reptibark), sifted to discard anything smaller than 1/8". I'll go as much as 50/50 pumice/fir bark for collected stuff or when I'm lazy, or drop the fir bark entirely for succulents like Portulacaria afra, etc.
To answer your question directly, I've never been able to overwater the species I have to the point that leaves start yellowing or roots start rotting. This is especially true in the summer when everything is growing and outdoors. With that said, I can (especially for tropicals indoors in the winter) water too much/too frequently to the point that I start seeing fungus gnats. That's a good warning sign that you need to back off. Other than that, I don't worry much at all about watering too much and tend to err on the side of watering the hell out of everything in the summer. A bonsai watered too much can usually be corrected. A bonsai watered too little one time might be dead.
Like everything, this is a bit of an "it depends" answer. Wind, temperature, hours of sunlight, humidity, container size, container shape, species, etc. all play a role. But no, generally, I find this mix (well sifted, with 3 inorganic components out of 4 total) to be pretty forgiving and have not had any issues with overwatering. The DE has the added benefit of being a reliable indicator of soil moisture, at least at the surface: it's dark when wet and bright white when dry.
