Many sources of coal ash are toxic to plants, I would not use it. The old
NCB did a lot of work identifying the toxic trace elements in some coal
ashes and on the selection breeding of strains of resitant plants to
colonise old pit heaps. Boron and I think copper at the 10s of ppm level
were the principal offenders. I occasionally pass the pit heap at Cefn Mawr
just south of Wrexham and it still has only a few isolated plants growing on
it after at least 30 years.
I don't know what particular benefit a non toxic source of coal ash would
bring.

"Cumberpach" wrote in message
...
I remember an earlier thread which indicated Wood ash was ok for soil,
although there is a tendancy towards alcalinity.
My adj allotmenteer has started to put soft-coal ash from his open
fire on
the soil. Is this ok please ?

Pete