What a difference a week makes! Our overnight low was 68! We will get well into the 70s today. I sure hope the cold was enough stress to insure a good bloom. I sprayed the trees with salt peter yesterday to help support a good bloom. We will surely have at least a couple more cold waves come by and it always seems like the last cold comes around Easter--sometimes cold enough for frost, so I will keep the covers handy.

28 in new orleans

........However the citrus are just the opposite-they have to be well watered to survive cold events-drought stress will just add to cold injury on them................

I was reading today in Walton Sinclair's book "The Grapefruit" and here is what it says in his chapter on freezes.

(l) Cooper et al. in studying the effects of drought on the dormancy and on the cold hardiness of citrus trees, showed that a 3 year old Meyer lemon tree could be protected from cold by maintaining drought conditions in the soil. The tree was not irrigated between November 12 and February 12 a period during which no rain occurred. ....using the tree-freezer technique, they found that the dry tree showed no injury until exposure to 26F for 3 hours.

(2) In the citrus growing districts of the United States, freezes usually occur in December, the preconditioning of the trees either by drought or by low temperatures during November is highly important in determining their cold-hardiness.

(3) Cooper et al reported on an experiment that occurred naturally in Texas during the 1949 freeze, showing the relationship between drought and cold hardiness. Many nurserymen had not irrigated their surplus stock for several months before the freeze. The nonirrigated nursery trees were all (100%) uninjured,, the irrigated trees in certain nurseries were uninjured, while the irrigated trees in other nurseries were severely injured.

This says that non hydrated citrus trees fared better that hydrated trees. What actually kills the tree in a freeze is that the water in the tree's cells freezes solid, which caused it to expand, thus kills the cells and the tree dies. I am not certain, but it seems to make sense that the less water in the tree at the time of the freeze the less internal ice expansion takes place and the fewer cells in the tree burst and are damaged or killed. ????????? I don't know as in Colorado we never have a problem with freezes unless the greenhouse heating system fails. Comments appreciated. - Millet

Wow-that is fascinating Millet! Perhaps I should treat my citrus like my succulents after all I remember in one of Dr.Coultas's lectures back in 1977 in my Citrus Culture class he told us that citrus should not be in any enviromental stress during a freeze to lessen cold injury-we were told that it is important to irrigate in the winter just as we do during Florida's dry springtime.I pulled down my old textbook ( Citrus Growing in Florida-Ziegler and Wolfe-University of Florida Press)-and found the statement on page 90-"However, a prolonged drought may put trees in condition of water deficiency which renders them more subject to cold injury than trees with adequate moisture content."However the research you cited refutes this conventional wisdom-and actually makes some sense- perhaps there is a limit to how dry you want to go-perhaps Dr.Manners can give us some additional wisdom.This is very,very interesting

Now this is very interesting. There must be two books with the very same title. I have the book "Citrus Growing In Florida" published by the University of Florida Press, but the authors are Larry Jackson & Frederick Davies, and your quotation does not appear on page 90. However, concerning cold hardiness, it does say all conditions that promotes a tree to be in a growing condition should be avoided. My book says it is the 4th edition. I wonder if that makes any difference. - Millet

If he's willing to give an opinion I'd like to hear from Dr. Manners as well. I gave my whole grove a good watering before the freeze because I thought it was best not to have them go into sub-freezing temperatures while water stressed myself.

.....Alan.

I certainly am not an expert here, but based on my knowledge of Chemistry and Physics, there may be two competing processes at work.

One factor I have recently read that makes the tree less susceptible to cold damage is that wet soil retains more heat and therefore can reradiate more heat at night.

I am guessing, but another factor that may make the tree more susceptible and is related to the internal freezing Millet mentioned is that in a drought state, the internal liquids may have a lower freezing point due to higher solids. Maybe Dr. Manners can add to that.

Joe, everything you said makes sense to me based on what I know. One thing I might add so that others may understand better is the process of protection by ice formation.

It is often said that ice insulates the tree keeping the trunk at or below freezing. I don't think ice is a great insulator (snow is due to the air in it). What happens when water is sprayed on the tree during temps below freezing is that the water gives up heat (1 cal/gram until it reaches the freezing point). When it actually freezes each gram of water gives up 80 cal of heat-- the opposite of the process of making ice cream in a churn where by adding salt and causing the ice to melt it and has to gain 80 cal/gram to melt.

This process is offset to a certain extent by evaporation during the spray application which takes away almost 600 cal/gram, fortunately vapor pressure is not that high at temps near freezing so not too much water evaporates. This process is also affected by humidity.

The point is that if one puts a nice coat of ice on the tree and then stops applying water, the ice temp may drop well below freezing, although by having added mass it will mean that more heat has to be removed to lower the tree temp than would be otherwise.

The protection temp from spraying water is also dependent on the rate of water flow. The seminar I recently went to in Fairhope suggested rates between 10 to 40 ga/hr and felt that the higher rate would protect trees to near single digits.

Once again they predicted 26 F & we only hit 30 F...

30 degrees here this morning. For what it is worth, the edition of Citrus Growing in Florida offered now is the 4th. So it would appear that there have been four editions over the years.

Ned

28f DEGREES THIS MORNING and snow started to fall last night around 10pm
forecasters called for 2 to 4 inches and turning to rain by mid morning ... it is now 2 pm and still snowing at 32f ( 8 inches later.... Blah) My 10 degree tangerine is under a pile of snow... I keep going out and shaking the snow off my palms

Greg