We did the same thing last year and we got below freezing quite a few times. It worked great! We planted the "frozen grass seed" in one place where our 3 dogs used a lot in the coldest part of the winter because it is right off of our patio and it was kinda brown. We used brand new bags on the side where we are putting in yard for the first time. The old frozen bag in the urine killed area grew twice as fast and looked better than the new bags did. All bags were the same brand. My husband said from now on he's buying grass seed at the end of the season when they are marked way down, letting them freeze and only using them. I thought he was kidding but when I asked him he said he really meant it!!!