New seed vs cold
I planted Scotts perennial ryegrass in plastic containers of potting soil inside the house. After grass sprouts were about 1-inch tall I moved one container to outside at 28 degrees for 24 hours. The second container was moved to a freezer at 19 degrees for 20 hours, (not cold enough), and then moved to a freezer at minus 4 degrees F. for four hours.
48 hours later the seedlings (left) held at 28 degrees were not damaged. Sprouts held at 19 and then four hours... at minus 4 degrees F. (right) were severely damaged. (Perhaps not killed--this will be determined after a few days.)