I think I used perlite and vermiculite last year for some Japanese Black Pines, maybe coco coir also. This year I noticed I have loblolly pine seedlings growing happily in absolutely everything in my yard. These are all self-seeded from trees in my yard, so it doesn't seem like they care very much if they have fancy soil or not.
Yes sir, just regular masonry/construction sand where all the smaller stuff is sifted out. I've been experimenting with different stuff over the years, this worked the best so far. I think it has something to do with how much air is in the mix.
I've already taken a lot of seedling cuttings from the tray, but a month ago it was absolutely full of trees.