I gave up long ago on mixes in bags, especially bags of opaque plastic so I can't see what I'm getting. Maybe I had a few bad expeirences with mixes that were mostly finely milled peat moss - I tend to overwater and haven't been able to break that habit. My first 2-3 years starting seeds drowned a lot of seeds!
Now I'm working off a batch of mix that started as about 10% commerical fine powdery milled peat (Miracle-Gro?) I gradually 'amended" it by adding 90% lighteners.
First, some coarse sand, which helped very little.
Then 20 Kg of #2 chicken grit, a big bag of coarse Perlite - big help.
At the same time, a big bag of coarse vermiculite: that may have helped open up more air space, but it held so much water that it may have hurt. And that vermiculite is probably breakintg back down into powder every time I dig into the bag of mix.
Finally I was turned on to shredded pine bark. I am now a pine bark groupie, and I sing its praises day and night.
My potting and sedling mixes are 70-85% screened pine bark, and 15-30% "everuthing else". When i finally work off all the milled peat moss blend, the only fines I will let in are the pine bark fines i can't easily screen out.
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There are expensive double-screened pine bark products, if you know a good nursery wholesaler or want to pay online shipping charges.
You can start with orchid bark, but where I see that for sale, shredded $1 bills would be cheaper.
You can start with dirty, soggy, smelly, half-fermented no-name woody junky mulch from Home Depot for $3.50 per 2 cubic foot bag.
I start with "nice" or "beauty" pine bark mulch, medium grade, for $7-8 from a classy nursery. They either keep it dry, or sell it fast enoguh that it doesn;t moulder on the pallet. No wood or dirt. Less "powder". Many nice long strands, fibers and chips.
I screen out as much of the fine stuff as I can. Anything that can be forced through 1/4" mesh by shaking bouncing or rubbing is too fine, and that gets turned into into my outdoor raised bed soil, or mixed directly with raw clay as I convert clay to soil.
I pick out the bigger pieces by hand and by pouring it rapidly down a 1/2" mesh.
For starting seedlings I don't want big chunks, so it has to pass very easily through 1/2" mesh and I still pick out big pieces by hand.
