Over the weekend I made up my substrate (growing medium) for the mushies. (for more details see Forest Fungi's website). But it was pretty straightforward. I mixed up some soaked oats, wheat and coir with some tea and coffee grounds and some gypsum, then put this into jars and number 5 plastic containers and used my pressure canner to sterilise.
Then put the grain spawn I received into each container and covered. Now I just have to wait for the mushies to start to appear - might take up to 8 weeks depending on how they like the climate in my house!