Sawdust mix for Catasetinae

[euplusia]

I have been using this mix over three full growth cycles now, for about 300 plants. So I can say it is tested.
I did not notice a nitrogen deficiency. I mostly use a balanced fertilizer, because I was afraid of rot when giving too high nitrogen doses. The sawdust does not decompose within the first year. And then I prefer to repot.
Pet Shops are often a good source for clean unexpensive potting media. Bird grit is an example.