Chris J Dixon wrote:
Ragnar wrote:
"Chris J Dixon" wrote in message
...
Having just extended a flower bed to incorporate what has been
lawn for 40 years, I am left with some pretty solid clay soil.

Gypsum is recommended as a soil improver, but appears to be sold
in garden centres as a proprietary product costing nearly £5 for
2.5 kg.

http://www.capitalgardens.co.uk/clay...er-p-6321.html

On the other hand, I can pick up a 25 kg bag of multi-finish
plaster for under £5, and AFAIK this is essentially the same
material.

Any reasons not to go with plaster?

I don't really know the answer to your question, but I would warn you not to
use gypsum if you want lime-hating plants such as heathers, rhododendrons
etc

Other sources seem to be of the opinion that one of the benefits
of using gypsum is that it is essentially neutral, and will not
alter pH.

Chris
I just checked, and its main constituent, calcium sulphate dihydrate is
mildly alkaline. giving a typical PH of about 7.4


If its the raw plaster of paris, its even more alkaline at a ph of 11+