Potash

I have large bonfires, very large, and spread the ash on the garden. The first time I did it I spread about two tons of it! Approx 1"+ deep and dug it in (but more of it into the heavy clay veg plot - which, combined with straw, helped to break the clay up). Everything grew like mad

Now, many years later, I spread a thin coating of ash every other year. It works very well - as those GC members that were here at the weekend can testify to

It's unlikely that a garden can generate more ash than can be usefully used.