Freeze report, 28-30F last night
Dropped to about 28-30F last night. It was a radiation freeze with strong inversion. Official station nearby said one hour below freezing and a low of 31F. The amount of damage says it was colder than that at my place. My thermometer said 30F at sunrise.
I spent nearly 3 hours covering things last night and managed to save some things.
Watermelon and sweetcorn covered fully with cardboard had no plant losses. There were just a few frozen corn leaves not well covered. The soil was warm as it was 90F two days ago.
Eureka persimmon with 3-4 inches new growth was covered with a tarp and 750 watt heater inside, no damage. I think this would have been 100% loss without protection.
Jujube with up to 12 inches lush new growth unprotected and no damage. Earlier small growth was frozen off at 25F. So I'd rate jujube as intermediate freeze tolerant.
Pecan has frozen leaves and shoots below 10ft but appears undamaged higher up.
Fig lost about 2/3 of new growth.
All unprotected apple, pear, and apricot fruits checked were frozen. But my experience says this shouldn't have been bad enough to take all the apples. So jury is out on that.
Grapes with 6-12 inches new growth and fruit clusters. 100% loss unprotected, 10-70% loss with some protection shown below. Covered with cardboard and low wattage cable heater inside.
Upper foliage and fruit frozen, lower unfrozen.
My conclusion is that to save a crop I need full coverage, ie tarp, and a good heater or passive heat source. Just covering without heat has not worked.