Mine have been very cold hardy here, with temps getting down to zero and below. They pile up on the floor of the coop, so make sure they have plenty of bedding to snuggle down in. The other most important thing for them is to keep them DRY in the cold weather! Silkie feathers do NOT shed water like regular hard chicken feathers, and they will get soaked to the skin! This is fine in the warmer months, and they love to play in the rain; but when it's cold and they get wet, they will freeze to death. Plan on putting them in a run with a roof on it to avoid them getting wet, and if it's very snowy, you may want to keep them inside the coop, or in a run where there is no snow. If they stay dry, I find they do much better in the cold than they do in the heat! We had an extremely hot and long dry spell here last summer, with many consecutive days of over 100*. I lost two of them due to the heat, and that was with misters going to keep them wet and cool. Good luck, they are a very fun and kooky breed of chicken!