no direct experience ...

but when i tried this ... w/o a greenhouse.. w/o humidity control ...

i had a hard time maintaining proper watering in individual cells ...

you have told us little of your setup.. other than you dont have space ... which sounds like it rules out a professional level greenhouse operation ...

i think you are throwing darts at variables.. and hoping to hit something magical ... sometimes it works .. usually it doesnt...

when i used to do hosta.. i moved seedlings at the two leaf stage ... they pulled right out of SEEDLING media

one might suggest.. that if you are knifing them out.. perhaps you waited too long to pot them up ...

perhaps we could intuit more.. with more facts of what you do do ... wink..wink.. i said do do ... crikey..

ken

Some coniferspecies for exampel root deep. like Pinus contorta and also Abies alba or Abies grandis.

Picea did fine, Doug fir was so so. I just have a couple of grocery crates. May be 80 * 50 * 40 cm (l * w * h). Put a plastic bag in it. I use cocopeat mixed with peat and vermiculite. Also used vermiculte with sand and peat etcetc. It all seems to be fine. Punch some holes 10 cm above the ground so excess water can seep out. To me, this works fine for Pinus contorta, Doug fir, Picea abies, lutzii, sitchensis, omorika and glauca, Tsuga heterophylla and sitchensis and lutzii like this a whole whole lot. The only species that does not do well is meyeri. They have survived for three years never growing higher than 10 cm. Meanwhile sitkaspruce and tsuga grow that in the very first season and then some...

For smaller-seeded conifers (Picea, Cupressaceae, and most podocarps), my setup is similar to what I've used successfully for succulents, only without the plastic bags. I have a mixture of 1/3/3 sand, copra or peat, and crushed perlite, which I put in 4" pots, scatter up to 20 seeds over the surface, and cover to appropriate depth.

For larger-seeded conifers (Podocarpus macrophyllus, Cedrus, and Keteleeria), I have a half-flat, in which I space the seeds about three inches apart, but otherwise use the same medium.

Since the medium I use drains very fast, I water at least every other day, more if the surface looks dry, and water until water is running out the bottom.

My issue isn't knifing them out, not yet anyways. I've only just started growing conifers from seed, and none of them are near that stage. However I've previously killed seedlings of Pinus strobus and Tsuga canadensis that I dug up from my mother's yard and tried to raise as bonsai, so I'm a little nervous I'll do the same here.