Here is part of an article in the link below. It also talks about clay
helping to buffer extreme temperature changes in the pots.
Based on limited research, clay may have these positive effects: increased
nutrient buffering capacity, increased cation exchange capacity, reduced
phosphate leaching, increased plant phosphate uptake efficiency, increased
water buffering capacity, increased water retention and availability,
stabilized pH, increased microbial populations and potentially increased
plant growth without increased water and nutrient inputs.
The reason I am curious about adding clay is because I had read previously
of its buffering qualities re pH. And, there are websites showing that in
Europe clay is being added to potting mixes sold at garden centers. I have
moved inland and an elevation probably 2700 feet, the air is very dry (nice
re botrytis) and the summers very hot and winters are getting darn cold. I
thought if I added the 8% clay to the mix as they experimented with, it
might be beneficial.
Here is another website quote:
Clay from http://attra.ncat.org/attra-pub/potmix.html
Several Canadian studies have shown that adding marine glacial clay (a
non-swelling mica clay) to sawdust significantly increases the size of
greenhouse-grown cucumbers and increases size and flowering of impatiens and
Anyhow, was curious if anyone was adding any kind.