I use glass petri dishes which I fill with sifted soil.
This assembly is put into the microwave and zapped for 2 min
on high to kill spores, other seeds, and bugs.

When cool I moisten the result and insert the seeds.

Is this OK? When I put the lid on the petri dish to retard
moisture loss, and make them stackable, should I worry about
oxygen lockout?

Please comment, Peter.