Answer: Based on your description I am not certain what is happening with your Italian Cypresses. That amount of cold alone without other factors should not have killed them back at the tips; they can handle substantially lower temperatures than 20F as they hardy into zone 7. I would suggest you consult with your retailer to try to troubleshoot the problem and based on that decide what to do. I'm sorry I can't be more specific for you. Good luck with your cypresses!
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