Todd_Renshaw

I have no proof, but just as a "thought experiment", I can imagine that even layered soil gets mixed somewhat during the process of repotting. (I use a chopstick with a circular motion to get the upper soil to sink into the large air pockets below and between the roots.) I think this probably blurs the boundary between where the smaller soil particles end and the big stuff begins. I suppose this would help tie the whole of the soil together and fight the perched water effect.

Another possibility; soil scientists think in big terms. Drainage on a large scale is a lot different from what happens in our little bonsai pots. Even if a perched layer exists in the boundary area inside a bonsai pot, perhaps it makes only a 1% difference. I'm always wary of scientific evidence applied to bonsai (even if it makes sense in the "real" world). I always doubt that bonsai fits in the parameters of whatever experiments have been done in the past.

As an aside, I'm not all that careful to separate my soil into many sizes. Partly because I don't believe it will make a huge difference, and partly because it's too hard to find different sizes in the soil ingredients I use. (But I do use some of the larger pine bark particles as my drainage layer.)

So my opinion is that I doubt soil layering is worse for the bonsai than using uniform particle sizes. Neither way is entirely right or wrong. (Which is best probably depends upon your watering habits and local environment too.) But for me and my habits, I see some benefit in using a larger drainage layer to fight the sogginess that must live at the bottom of a bonsai pot. (I just won't expend too much energy on separating my soil into various sizes. Too much trouble. No thanks!)