Trisha, coal contains sulphur which is harmful to plants. This is why we don't use it in compost. I have never thought about using it beneath bark to reduce weeds - I suppose that this could be an idea.

It is only really safe to put on standing out areas or paths, as we did when we used solid fuel boilers years ago.

but becareful that it wont wash or leach into the surrounding soil. :o)

My dad always dug our ash etc into the garden and we had excellent fruit and vegetables, and it hasnt killed us of. Plus he used to sprinkle it on the paths in the back garden in the winter months

Mind you we did have clay soil where we used to live

Your dad might have been using wood ash, Hijuju, which is fine on the garden. Coal ash isn't - you can use it on the paths as long as there's no adjacent planting areas onto which it may be washed by the rain.