we put a off cut of a treated post in the pot belly and closed it down about 1 minute late there was a defining explosion and the glass in the front of the stone was on the floor and the chimney was crocked.
we burn all treated offcuts outside in a big heap of garden waste. but i live in the contry so it has no one to hurt.
re potash in the garden?
it is good as long as you haven burnt treated timber or camphor laurel as these relise chemicals and will halve the rate of grow of the plants planted in that soil compared to untreated soil.