It is recommended that any material not specifically produced as substate be place in an oven at 80-90 degrees centigrade at a maximum thickness of 3cm for 2-3 hours, this will remove excess water and kill any bacteria or mould. Hotter temperatures are not required and may burn the substrate releasing poisonous chemicals.

You should also be aware that some garden wood mulches contain chemicals to stop mould, deter slugs and snails, etc. These should not be used.