On 02/10/2016 08:35, Chris Hogg wrote:
On Sun, 2 Oct 2016 07:46:13 +0100, Stuart Noble
wrote:
The recent Joanna Lumley programme about Japan visited a volcanic island
in the extreme south where the world's largest radishes are grown. I
can't figure out why a pumice rich soil would be any different to
vermiculite or perlite, all 3 having the same properties of air and
moisture entrainment. No mention of nutrients, but there must be some in
volcanic soil? Puzzled...again.
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Not sure this is telling you anything you don't already know, but
volcanic soils world-wide are exceptionally fertile. The slopes of
volcanoes are extensively cultivated for growing crops. The ash in the
soils keeps the structure open and free draining, but at the same time
retains moisture (that sounds a bit Irish! I'm not entirely sure how
it works). The minerals and chemical elements released when volcanic
ash weathers further contribute to the range of trace elements
available for plant nutrition.
I think these things *entrain* moisture, but they don't absorb it. Yes,
it's Irish but the amount they can "hold" is phenomenal, and yet they
dry to a reusable powder. The idea that you can use them to fill
containers on balconies is flawed because, although they seem ideal when
dry, they are extremely heavy when wet!
IME vermiculite is surprisingly quite alkaline due to the presence of
calcium (I think it's on the cation exchange sites, to be boringly
technical). I also find it tends to break down and eventually go
rather claggy. I use perlite in preference, which should have similar
properties to volcanic ash as it's made from weathered volcanic glass,
obsidian*.
A couple of years ago, I saw packets of some sort of 'rock dust' for
sale in my local garden centre, with much printed on the packets as to
how wonderful it was for growing plants (BTWSTWT!). Can't remember the
trade-name, or whether it was specifically ground volcanic ash or
lava, but most quarries with stone-crushing facilities have piles of
discarded dust, as it's too fine to be used for roadstone or
construction work. Perhaps one of the big quarrying and roadstone
groups was branching out. I'm sure if there's a quarry near you,
they'd be happy to let you have a few bags' full for nothing if asked.
Or you could take a trip to Mexico ATM http://tinyurl.com/gv2lor2
*https://en.wikipedia.org/wiki/Perlite
I buy the 100L size vermiculite from builders merchants and, as I have a
small garden, I can use it everywhere. Mixed 1-4 with compost it stops
the soil compacting and makes it dead easy to weed (things just pull out
by hand).
What I can't figure out is what it, or volcanic ash for that matter,
might contain in the way of nutrients to produce the world's largest
radishes! I suppose no amount of feed is any use without a good soil
structure
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