BioChar?

I think you do need to consider the cost of these products, not only to our pockets but in terms of journey-miles to the plot, and whilst it is clear no-one here is thinking biochar is a miracle worker, if it is part of the bonfire remains being dug into the plot, then it will be a useful addition overall.

My Mum always said charcoal was good for you 

Mind you, that was on mornings when our toast had black edges