"Kay Easton" wrote in message
...
In article , Jason Pope
writes
Kay Easton wrote:
In article , Jason Pope
writes

Victoria Clare wrote:


I piled it all in a heap under the hydrangea, meaning to do something
about
it later. This produced a strange effect: the side of the hydrangea
next
to the little pile of rusty things is now a vibrant blue, but scales
through purple to pink on the other side!

I've now distributed the items more evenly around the plant, and hope
it
will all be blue soon. They are hidden under a layer of mulch.

Victoria

The rust from the nails alters the soil pH which causes the effect you
mention, it is grounded in good science!



Can you elaborate on that? I thought rust was iron oxide, which I
thought was alkaline, but hydrangeas go pink, not blue, in alkaline
soils.

Are you sure it's a change of pH that's having the effect, rather than
greater availability of iron?


From a website:

http://www.nobleplants.com/articles/...0history%20&%2
0cult
ure/care%20&%20culture.html

snip explanation of availability of aluminium depending on pH

OK - that's fair enough ... but where does the iron come in? Or did I
miss something?

I have not yet read the URL referred to up above here, but I would be most
surprised if it said that bluing of Hydrangeas is very seriously connected
with Aluminium. My understanding is that it is primarily the availability
of the correct ion of Iron which determines the bluing. Iron exists in two
ionic forms, one of which is involved in the blue dye of Hydrangeas. In the
wrong kind of soil, the desirable ion is rapidly converted into the wrong
one, thus preventing the blue dye from be synthesised in the plant.

Franz