On 14/12/2014 17:13, Tom Gardner wrote:
On 14/12/14 16:08, stuart noble wrote:
On 14/12/2014 15:35, 'Mike' wrote:
Thanks Bob. It is actually volcanic soil I am interested in improving,
but we have a heat and lack of water problem. My very inexperienced
thoughts are that the compost would add body.


I thought volcanic soil was the ideal growing medium in terms of
nutrients and
water holding capacity.

While volcanic soil can be very good for some crops, I doubt it is for
those reasons.

The volcanic areas that I have seen are /very/ dry, since the "soil" is
very porous and completely without clays.

Example: Iceland. All volcanic. Very dry surface in many places despite
the high rainfall. Normal temperature range on the periphery: 0C to 20C.

20% is "green and fertile", but that only requires a 1 inch diameter
tuft of grass every foot! Yes, they do grow tomatoes and bananas, but
only in greenhouses ObJoke: Q - what do you do when you get lost in
an Icelandic forest? A: stand up.

I only have experience of perlite and vermiculite, both of which can
hold huge amounts of water, so I'm not sure why Iceland is so porous.

As I recall the southern tip of Gran Canaria is virtually devoid of
living things. I was told it never rains, but it did the day I tried to
get a taxi to the airport. Sheets of the stuff!