Funny that this should come up just now. I'm to give a talk on "soils"
for my Gainesville Bonsai Society this weekend. I took this as an
opportunity to do a little experimentation. I built a box about (4" x
4" x 6" high) out of clear plastic, marking the height on the inside for
measuring. The bottom was made out of my standard pot screen (7x7 space
plastic canvas). I figured that if there was a perch, it would be at
the screen and that this would most nearly represent my potting
condition.

As a result, any of the "soil" material which did not go through a
standard window screen, did not perch. Material tested we pea
gravel, perlite (expanded shale, I think), vermiculite (expanded mica?),
baked clay (similar to Turface), shredded pine bark and peat moss
(unscreened, i.e. straight out of the bag). Only the peat moss perched
over the screen, about 1" high.

I then tried the peat moss over both the pea gravel and the perlite (two
different tests). As advertised, the peat moss perched over both but as
the water passed slowly through the peat moss, the pea gravel and
perlite both drained quickly.

Please note that the tests were made with total bottom screening. I
have not yet done the tests with just a partial drain hole in the
bottom. That might make a difference.

My analysis of the tests is that perching can indeed occur in bonsai
pots but the "soil" material would have to be fine enough that capillary
action can take place. If no fines are allowed, no drainage problems
should occur in a properly built pot. However, if a high percentage of
fine material is used in the mix (such as peat moss for azalea mixes)
then a drainage layer might be a positive benefit. In this case, I
think I would use a deeper than normal pot to allow the drainage layer
enough space to be effective and give the roots some breathing space.

It was fun to see "inside" a pot!! Have fun - jay


Jay Beckenbach - Melrose, FL - Zone 8b/9a -

-----Original Message-----
From: Roger Snipes ]
Sent: Sunday, September 11, 2005 12:44 PM
Subject: Question and advice please ... Bonsai Soil

Of course a perched water table can be a bad thing, but I don't think
that
bonsai pots with layered soil end up with enough of a defined layer size

differential to actually create one; I think the layers get somewhat
blended, especially with all the action of working soil in around the
roots,
etc. when potting. Therefore, I think that layered soil in a bonsai pot

does no harm.

---------- CLIP ----------
Marty layers his soil and notices a preponderance of roots in the bottom
of
his pots in the drainage layer. I don't layer my soil, and I use a mix
similar to Marty's, i.e. crushed lava rock in the 1/8" to 3/8" range,
and I
also notice a preponderance of roots in the bottom of my pots. I think
this
is a normal situation because it is always moister there, drainage layer
or
not.

My conclusion is that if one uses a coarse, free draining soil mix
layering
the soil will probably do no harm, and will also probably be of no
additional benefit.
---------- CLIP ----------

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