Mini Pine Barks are sold by various big box stores. I use this with pro-mix, original seedling with growing media and Osmocote Plus when I upsize out of rootmaker 18s to root pouches.
In order to be clear and not mislead folks, the photo below is the exact product I purchase.
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Three big advantages to using this product: 1) improved drainage, 2) cost less than pro-mix, and 3) helps with pH
I have a hard time finding vermiculite so I just substitute more perlite. Might not be the right thing to do but my trees don't seem to care.