A very large conifer was blown down here a while back and it is going to leave a correspondingly very large stump.
Back, half a lifetime ago, and more, there was a treatment that could be used to produce a very long smouldering burn of the stump. This was mentioned to me by a professional forester, and was "something" that was used to fill holes drilled into the stump and left to migrate through the stump, before lighting the blue touchpaper.
My memory says it was ammonium carbamate. Has anyone got a more definite recollection and, preferably, experience?
Potassium nitrate is suggested online, but I am unconvinced that, if applied and patience is exercised, a slow smoulder would result!!! But I am willing to be convinced otherwise.