On Mon, 01 Jun 2009 18:14:53 +0100, Chris Hogg wrote:

Is there a straightforward additive/antidote to reduce pH?

Two approaches: water once with a solution of Sequestrine, a complexed
form of iron soluble at alkaline pH's and available in sachets from
garden centres, or if the plant is in the soil and not in a pot, add a
teaspoonful of vinegar to the watering can to acidify the water. You
can do this occasionally if the plant is in a pot, but the salts may
build up with repeated waterings as they don't get flushed away as
they would in the soil. Of course, the second approach only works when
using a can rather than a hose, but once you've used Sequestrine, you
can use the hose without worrying.

I'm in France at the moment and couldn't find Sequestrine (or sulphate
of ammonia, come to that), nor could I spot an equivalent product in
the garden centre here so I'll go with the vinegar for now until I get
back to the UK to pick up supplies.

Thanks again.