Soil advice

Jane McGary via pbs
Wed, 21 Oct 2020 10:00:34 PDT
My only experience with "decomposed granite" was in my brother's garden 
near Monterey, California. There it's used for surfacing paths. As 
available there, it contains a lot of fines and sets up like concrete 
when dry, but will soften when wet. However, "granite grit," which is 
available here in sacks and is used for various things such as 
topdressing pots and (I think) as turkey grit, does not contain fines. 
So David in California should be careful to use a "washed" product, not 
one with fines. On the other hand, I prefer unwashed pumice for the grit 
component of my potting mixes, because the fines provide some nutrients, 
and it doesn't set hard even when used without other materials, such as 
for rooting cuttings. I think only washed pumice is available in small 
sacks, and only one supplier even here offers the unwashed product. I'm 
told the pH of this material is near neutral. Another good sort of grit 
is quarter-ten crushed rock, but the resulting pots are very heavy.

There is a very detailed discussion of soil mixes ("composts" in British 
usage), by Louise Parsons, in the book "Rock Garden Design and 
Construction," which I compiled for NARGS some years ago. It's probably 
available used.

Jane McGary, Portland, Oregon, USA

On 10/21/2020 8:41 AM, Bob Hoel via pbs wrote:
> Another term for decomposed granite that is used here in the midwest is rotted granite.  I will use it in my soil mixes to provide good drainage.
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