Here are two links to some interesting articles about frost protection:
The fao link is 7 or so chapters long, you have to use the arrows on the page to advance chapters. It has a lot of technical information:
http://www.fao.org/docrep/008/y7223e/y7223e06.htm#TopOfPage
The next link is more of a novelty read from 100 years ago describing some interesting ways people battled with frost events in the past, including using explosions! :