First thing I learned a few years back was the fact that if the weather forecast is showing 34f (as it is above, for Saturday)....it will be 3-4 degrees colder out here! We are looking at 31f and the Orange Trees are already screaming for their blankets.
Second lesson learned.....use two layers of burlap on the trees. A single layer still allows a thin coating of ice on the leaves......two layers creates a thermal barrier. I have a system that I came up with on how to cover a citrus tree, Farmer Deno will be doing a detail post on this in a few days from now.
Thirdly.....turn on the irrigation system to wet down the ground beneath the trees.........during the hours of frost. The water temperature is vastly warmer than the air ....so you'll get radiating heat. Just think of the love you need for these trees......to be running around at 1:00 a.m. in the dark.....turning on the water and double checking the burlap covers. Hell....I give em them trees a little hug out there too!
Back in my young years living with my folks in Los Angeles, the late 50's......I remember the smudge pots (also known as a choofa or orchard heater) burning diesel fuel, in all the orange groves of the area. Yes....Los Angeles, San Bernardino, Orange, and San Diego Counties were blanketed in Orange Groves. The tractors tearing out a orange grove over in Orange County we saw one day.....I must had been 3 or 4 years old....was clearing the land for some joint called Disneyland.
If I want frozen orange juice, I'll skip the tree hugs.