I agree with Christine. If it's frozen, you might have to extend the time. I live in the PNW and I don't make
biochar in the winter, because it's so wet, cold and dark. I usually inoculate for a week. It has been freezing when I inoculated, but it has never been continually freezing for the whole time while I inoculated. Usually, it's only freezing for 2-3 hours from 4-7 am, and above freezing for the rest of the day. I don't extend the time then.
John S
PDX OR