Iris Cohen wrote:

Brent at Evergreen Gardenworks wrote:
The major cause of soil collapse is loss of particle size due to _composting_
of the organic portion. By using composted bark, you are using a material that
already has one foot in the grave.

I'm a little puzzled at this. Fatal soil compaction results from using organic
matter that is too finely ground or too soft, like peat moss. The pine bark
that is generally used in commercial bonsai soil, like Hollow Creek Farms, is
only partially composted. This is to prevent the problem of bacteria in fresh
bark using too much nitrogen.
Also, if you repot on a regular basis, say every two or three years, the
organic matter won't have turned to mush that fast. Another cause of premature
soil collapse is using an inadequately fired clay component, like cat litter.
That is why we keep emphasizing the need to use a high fired product like
Turface.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

I guess I'm as puzzled as Iris. I have begun to pot my deciduous trees in 2/3 -1/3
organic and inorganic soil, the organic being a combination of pine or fir bark,
not composted, and my own compost. The inorganic is mostly turface and some fine
gravel. It would seem that with regular repotting, as Iris points out, the soil
compaction will not be a problem. If a person were to wait too long, like 4-5
years or more, then I could see it being a problem.

And, of course, the climate is all-important. My soil mix would not work for
someone elsewhere. I've even changed my mix moving from Maine to here in southern
NY state, accounting for hotter summers.

Craig Cowing
NY
Zone 5b/6a sunset 37

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