How come citrus farmers spray water onto trees the night before the temperature drops below freezing?

Question

I know it's done to protect their crops, but in terms of energy lost/gained how does it actually protect the crops from damage?

Answer 1

water freezes at32 degrees and stays there. The ice insulates the fruit from temps dropping further than that and actually freezing the fruit'

Answer 2

Actually what you are seeing is only part of the process. Irrigation prior to a freeze is best done a couple of days prior to the freeze. Moist soil will hold more heat than dry soil, if the farmer has time to irrigate and let the sun warm up the moist soil. Irrigation just prior to a freeze can actually cool the soil, as wind blows over the soil surface, evaporating the water.
Water sprayed on the leaves can protect any plant from freeze damage, with a couple of VERY important provisos.
Water has to be applied CONTINUOUSLY after the temps reach freezing to the point at which temps rise above freezing, usually the following morning. The continuous flow of water keeps the ice which forms, and therefore the plant, at 32 degrees. Without the continuous water flow the temperature will continue to drop, causing MORE damage to the plant than would have occurred if no water was applied. Also it takes a lot of water to cold protect with this method. Something like one inch per hour. If less water is used, the temps drop and the freeze/ice damage will be more severe than if no water was applied.
Modern citrus groves use micro-sprinklers placed under the trees. These are turned on during a freeze, and help keep temperatures above freezing under the canopy of the tree. In a severe freeze (citrus is not damaged until 27 degrees F) outer branches and fruit may be damaged, but the trunk and main branches can be saved.

Answer 3

Yes it actually does. What they have to do is spray the water just before the
sun hits.
They also use things like salamanders/ smudge pots that use oil or kerosene to keep the cold pushed up so that frost can't settle on the blossoms. You had to stay up all night long to keep fuel in them. Citrus farmers are not the only farmers that do that.
Salamander heater in the 1940s, sales spread across ...
The photo below is called a smudge pot but the real name is salamander heater
http://www.flickr.com/photos/clintriter/432351860/
Smudge pot photo
http://www.flickr.com/photos/looknfeel/486068282/
Photos of the 2007 Easter freeze
http://www.scenicvieworchards.com/Strawberryspring.htm
I used to raise and sell chrysthemums and had to do it several times to keep the buds safe.

Answer 4

as we were taught in Korea, snow or ice freezes at 32 deg, any thing below it will stay at 32 deg or higher, so will be protected from lower temps,
we had to sleep in sleeping bags, under the snow, to stay warm,

Answer 5

Moist soil does not freeze as easily.

Answer 6

the water will freeze and not the fruit it is protected by the ice