On 14/12/14 17:58, stuart noble wrote:
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.

There are many types of volcanic "soil", of course. Much is sand made from
ground-down basalt. I have some that floats on water, with 90% above the water.