In article ,
says...
Sacha wrote:
On 5/3/08 17:50, in article
, "Jeff Layman"
wrote:

snip
You might find this site interesting:

http://www.gardeningdata.co.uk/soil/...john_innes.php

Yes, thank you, I had forgotten about that site.

But, unsurprisingly, it doesn't show any of the original research results
which led to the JI composts. Neither does
http://www.jic.ac.uk/corporate/media...ic/compost.htm or
http://www.johninnescompost.org/cms.php?pageid=5.

In fact, with the ref you gave, I learnt something which puzzles (and I must
say, annoys) me. And that is the information about JI Ericaceous compost.
I use that a lot, as I grow quite a few plants which don't like chalk. I had
originally assumed that it was JI3 without chalk. However, according to the
link, it is JI _Seed_ Compost (with sulphur instead of the limestone)!!!
Why Seed compost? Is it assumed that ericaceous plants wouldn't like a
little more NP and K? It is true that some of them are well adapted to poor
soils such as heathland, but is it assumed that they would not tolerate the
extra NP and K in JI3?

Or is it that the same price is charged for a bag of Ericaceous compost as
for JI3? Sulphur must be pretty expensive, then, compared with the other
(missing) ingredients.


I think that plants growing in ericaceous soils are better able to access
plant nutriants (but not some minerals like iron) than those growing on
alkaline soils so my guess would be that the nutriant levels do not need
to be as high for the same results. As for the cost, it could be more to
do with where the loam comes from and the transport cost involved rather
than the fertilizers put in.
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea