Jose and I checked the citrus crop last week. These are grapefruit and as you can see we have a good crop for these relatively small trees. As winter sets in and frost threatens we have to turn our attentions to protecting the crop. We protect with water from sprinklers that we set up in the orchard. I have ordered new lower output sprinkler heads for this season. Frost often happens in a series of up to six days so if we water all night for this time by the end of the period the orchard is soaking wet and the the roots of the trees can become asphyxiated. These new sprinkler heads use only half the amount of water so we hope to alleviate the problem.
As the water lands on the ground or tree it freezes and gives up a large amount of energy in the process (latent heat). The tree can be covered with ice, the outside air temperature can be 5 or 6 degrees less than the temperature of the tree under the ice protection.
On Friday morning I took this picture below. It was not so cold but i decided to turn on the water as the cumulative cold over the past five days was significant. This is a very small amount of ice for the tree to handle.