I now use 80% sand 20% worm castings. It seems to be the very best mixture for growth. Very nice healthy fat seedlings come from it. But you don't want to bake it with the worm castings in. Sterilize the sand then add the worm castings afterwards to keep the nutrients alive.
Absolutely the way to go from what I have seen and New Wisdom and Nanashi are on the money it seems.
In a side by side test I saw recently, that had many cacti varieties from many vendors the difference was truly amazing.
Straight sand was about 20% strike, and growth so slow it wasn't even noticeable. He said he was very disappointed and wouldn't bother doing that again.
Sieved oven baked commercial/premade "Cacti mix" was 33% strike. Reasonable growth and none of the algae and fungal issues he had expected. He had assumed all would probably die, was pleasantly surprised, and said I should definitely try that if I cant get worm casings.
But the oven baked sand with uncooked worm castings was the winner by far.
57% strike rate!(and some of the varieties NONE of the seeds had struck in the other mediums)
All were fat healthy little seedlings that looked about 3x bigger than the others.
The dude had split the whole test into 6x individual 96liter clear plastic "roller boxes" with lids, each containing 77 disposable shot glasses with a hole in the bottom for drainage.
462 individual "pots" for about $7.00 he said, which sounded pretty good to me.
All of the containers were being opened and watered 2x a day, with 3 of the containers being treated with "Fongard" systemic fungicide(250g/kg FURALAXL) in a sprayer.
The other 3 being sprayed with normal rain water 2x a day.
None of the boxes had any algae or mold issues, and the chemical had no effect on germination or growth rates, so he said he wouldn't bother using chemicals in the future, which made me happy. lol.
I hate all that chemical nonsense and it was nice to see I wouldn't need it if I ever moved south and decided to start some cacti seedlings myself.
20% casings 80% baked sand, clean sterilized box, good drainage(he had the little shot glass pots sitting on an oven rack about 2inches off the bottom of the box).
Definitely the way to go!
I might even start a few dragonfruit and opuntia seedlings like that, as it obviously worked really well.
Sort of copied his setup and am going to try growing a few of my more expensive seeds and rare passiflora like that, and run a bit of a test with the acacia later on, then move them out into pots once they get a decent root down.