I just got done throwing out my old medium (sphag or bark mix) around the base of my Metasequoia glyptostroboides. Type that one into google and see what it is. he he he he he he... do it.
I love these trees Chas!! Dawn Redwoods are fantastic, I have one growing as a bonsai!!
As fgr what I do with my old media, I like to put it in the compost.
I use mine as a top dressing on my roses and fuschias in pots, and the rest as top dressing in the flower beds. Since I also collect other club members' bags of used bark which they would ordinarily put in the trash, my top dressing in the garden is quite thick but gets turned over in the spring.
It's the compost pile for all of my old potting media. It gets to play with lots of other stuff - like vegetative material from the lawn and gardens, the chicken "droppings", etc. etc. and within about a year, it comes out as excellent garden soil! Waste not, want not!!!