Hi Bart,

Growing Sorbus in general is an easy thing if the seeds are viable and fresh. I think they are pretty much the same, just sow them into an average mix. I am mostly covering the seeds with few milimeters of the same mix than with grit, but sowing them on the surface than covering them with grit should be also fine. I am mostly keeping them outside, however i have no experience with the mentioned species, mostly growing Eastern-European species. Good luck with them!

Máté