http://www.panhandleparade.com/index.php/mbb/article/satsumas_survived_the_freeze/mbb7720997/

Satsumas Survived the Freeze

01/22/10 - 02:52 PM



Jackson County, Fla:

Farmers don’t easily forget harsh weather, according to Mack Glass, a Satsuma farmer in Jackson County. When asked if it had ever been colder than this month’s chill, it only took him a second.

“January 23, of 2003, we went to 15 degrees with very small trees,” Glass said. “And I remember the day because we thought we lost all the trees—but amazingly we didn’t lose one tree.”

That was the coldest it’s been since Glass planted his first citrus trees in March of 2002. But the recent freeze was the longest period of continued cold. He said it had Jackson County citrus farmers feeling a little nervous.

“We really didn’t know what to expect. We had never experienced that many nights of high teens, mid teens, and low twenties.”

History shows cold isn’t very kind to Florida Oranges. Once called the Satsuma Capitol of the world, a 1934 freeze destroyed acres of the county’s citrus groves, and put an end to the Panhandle’s citrus dominance. Freezes in 1985 and 1989 destroyed many of the citrus groves around Orlando.

But the latest freeze wasn’t nearly as destructive.

“After walking through the grove and looking through the trees now, we’re optimistic that the damage is going to be minimal and we will be able to harvest next November,” Glass said.

Glass reported he didn’t lose a single tree during the cold weather period, and attributes that accomplishment to better technology than anyone could have dreamt of in the 30’s. Farmers are now able to spray their trees with water during extreme cold, and the melting ice creates heat for the tree to survive the frigid outside air temperatures.

It apparently worked, and damage is minimal.

“It’s actually broken a few limbs but nothing drastic, we’re seeing some twig damage but not a lot,” Glass said. “Like farmers are, we’re always optimistic that we’ll get through this.”

Read more: http://www.panhandleparade.com/index.php/mbb/article/satsumas_survived_the_freeze/mbb7720997/#ixzz0dUtZRLnM

The reporter has it backwards--it is the freezing of ice that releases heat--melting of ice requires heat.

This is a difficult concept if you don't have a science background.
Although some teachers don't approve, I think here the concept of 'cold' or 'coldness' is useful. The idea of heat being released by freezing water is not very intuitive. The idea that 'coldness' is required to create ice is much more understandable.
It takes a lot of 'coldness' to cool water and then create ice from water. If the water wasn't there, this 'coldness' would significantly lower the temperature of the the air, the ground and vegetation. So, freezing lots of water absorbs lots of cold - which is equivalent to providing heat.
Also, the ice is always initially formed at 0C, 32F and if it coats the vegetation, it then provides an insulating layer against further drops in air temperature.

There are actually several factors at work--the "heat of fusion" where water releases approximately 84 calories/gram as it freezes--at the same time any water that is evaporating is taking away about 540 calories/gram. It also requires 1 calorie/gram to cool water 1 degree C.

There are also several processes involved in the transfer of heat--contact transfer of heat between the air and plant (or water), conductivity or transfer of heat within the plant or water, and radiation where all matter radiates (heat in the form if infrared radiation). As long as there is liquid water present, the ice cannot go below 32 F--that is the biggest factor in spraying water to protect the plants--the insulation factor is not very important until the all liquid water is gone.

The use of containers of water placed near the tree (ie 5 gal buckets) provides a mass of water that releases heat as it freezes and gives off infrared radiation.

The heat involved in phase transformations is not that hard to understand--in our high school chemistry class, we made ice cream using an ice cream churn as a demonstration of the "heat of fusion" in reverse.

The physics and maths of what you describe is all correct, but the 'release of heat' from a bucket of freezing water is I think misleading.
It doesn't magically transfer a dollop of heat to a nearby tree. It's not that heat is being released by the freezing - rather the water is freezing because heat is being removed. And it's being removed by conduction & convection to cold air, and by radiation to the night sky. The tree won't get very much!

Using a 55 gallon drum of water as an example, I think the water in the drum absorbs heat during the day-when its warmer -then releases the heat at night when the temps drop. I think in the hot summer the same drum of water will help keep a green house cooler if it's able to absorb heat during the day and releases the heat at night when the temp is cooler but in both situations that I describe the drum is inside an enclosure. when it gets very hot in the summer I would have a 2 speed oven -hot and hotter unless I open everything up or turn on fans and a/c. I do not have a green house but I do want one .

I guess three drums around one citrus bush would even help outside unless it was too cold at night . Not sure exactly what too cold would be...
I have not used drums yet. I use large heavy cardboard boxes and large old fastioned Christmas tree lights on cold nights ...rain is not good for cardboard boxes.

A 55-gallon drum filled with water contains 440 pound of water (456 with the weight of the drum included). As it takes 1 BTU to raise 1 pound of water up one degree F., so it also gives off 1 BTU of heat when one pound of water loses 1 degree F. Therefore, for every drop of one degree, a 55 gallon drum of water will provide 440 BTU of heat to a greenhouse. In Colorado the average drop in the water temperature over night in a 55-gallon drum of water is 4 to 6 degrees, or 1,760 to 2,640 BTU's of heat per drum. My greenhouse has one hundred 55 gallon drums, which beside proving me with nice greenhouse benches, they also generate 264,000 free BTU of heat every single night, almost TWO MILLION BTU of free heat per week (plus the cooling during the summer as Tom wrote. - Millet (1,084-)

Wow Millet! I sure would like to see a photo of your drum setup. I had seriously considered putting a couple of drums painted black (filled with water) inside my house for the winter, but never got around to getting it done. Do you have them stacked?

Citrusgalore, no, the drums are not stacked, because I use them as benches. The plants I set on top of them, do really well due to the bottom heat (approximately 60 to 70F during the winter months). The south side are painted black to absorb heat from the sun's rays, and the north side are painted white to reflect light in the greenhouse. You can see them in the link below. - Millet (1,084-)

link

Yes, now we agree. If the tree (with bucket of water) is covered, then warmth from the water will be trapped. It is approaching the greenhouse condition where - as in Millets greenhouse - stored heat is first transferred to the interior and then is more slowly lost to the outside.