Old mix that I am reuse may have some perlite in it, but I have not been adding it to new mix since I discovered vermiculite.
I don't sterilize peat and vermiculite mixtures, but if I add top soil to a mix for seed starting, I sterilize the top soil in an old microwave prior to mixing. Mostly, however, I am using peat and vermiculite mixtures for seed starting, and the plants seem to approve.
