Protecting Citrus from the Cold

johnorangeJanuary 7, 2014

I'm finally done with all I know to do to help my citrus trees through the night. My trees are all in the ground so no way to bring them inside. Our low is supposed to be mid twenties and some say upper teens.

I covered my kumquat tree with's about 8 ft tall. The tree will probably be just fine but this should keep the fruit from freezing.

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I'm trying something new tonight for five large lemon trees that are just too big to cover.

I call this my redneck smudge pot :>)

Share your in-ground protection methods. Did they work?

    Bookmark   January 7, 2014 at 1:02AM
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A small smudge pot, or orchard heater is a big help, if a bit costly; add a rotating fan and you can raise temperatures 10F or more.

    Bookmark   January 7, 2014 at 4:54AM
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Another good method is misting sprinklers; you won't think they work, because you will have ice everywhere; but ice is 32F and won't kill many citrus. The water gives up heat in converting from water to ice.

    Bookmark   January 7, 2014 at 4:56AM
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Thanks Johnmerr, I had a box fan on the step ladder but an oscillating fan would have been better. My trees (the leaves) looked pretty rough this morning. I think misting the trees would help seal in the leaf moisture as well as providing some thermal protection. My leaves are crispy so most of them will drop. The temp this morning in one of the unprotected trees was 19F.

My kumquat fruit I checked this morning were frozen solid so I may not have saved the fruit.

    Bookmark   January 7, 2014 at 9:44AM
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Here is a discussion of ice, some in fun and some a little more technical from my biologist background. I have surprised people before talking about cold ice and warm ice (my tongue-in-cheek terminology). "Cold" ice cubes will stick to your hands when you handle them but "warm" ice will melt in your hands. If you are making ice cream with ice and salt in an old-fashioned freezer, the best ice is from your coldest freezer. Water freezes at 32F and it does give up heat turning to ice but once it's ice, given enough time, it will get as cold as the environment around it. I suspect the ice on a tree leaf may get colder than 32F but certainly the ice acts as an insulator in several ways, otherwise it wouldn't help. The layer of ice has to be cooled before the leaf can be further cooled so that gives more exposure time protection. Would it also be intuitive to say leaves produce some internal heat through their biological activity and the layer of ice helps retain this "heat" in addition to sealing in the leaf's internal moisture?

    Bookmark   January 7, 2014 at 10:08AM
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Sorry, John, you were going so well until you got to the part about plants producing their own heat. I'm pretty sure plants are not homothermic; they only tqke on the temperature of the air and soil around them; and t think technically photosynthesis requires heat rather than producing it... but at or near freezing there is little of that going on... at least for citrus. As for sealing in the moisture, I think any moisture near to the ice coating will tend to become ice and as such could produce a tiny amount of heat from the conversion. Anywtay, it is an interesting discussion. Commercially, citrus producers today almost universally use sprinklers from well water to combat frost. Well water tends to be around 60F and gives off more heat from converting to ice. The biggest and best also use helicopters to stir the air; but nothing comes close to water for frost protection... not even orchard heaters.

    Bookmark   January 7, 2014 at 11:24AM
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LOL! Johnmerr, I agree the internal heat hypothesis may be skating on some thin ice.especially at low temperatures.

    Bookmark   January 7, 2014 at 4:18PM
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This heat question is still bothering me some. Kind of like a song you heard one time that won't go away. Not so surprising I suppose, but a search on the topic lead back to Gardenweb. I included a link to that discussion. There seems to be some agreement that plants produce heat through respiration but transpiration, a cooling process, probably results in more cooling than the miniscule amount of heating.
The bottom line? Obviously is that it's a really great thing if you can mist your citrus when it gets really cold!

Now I'm wondering if I could submit a scientific research paper that proposes global warming is caused by too many weeds in our gardens. :>)

Here is a link that might be useful: A discussion of house plant heat

    Bookmark   January 7, 2014 at 5:53PM
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Trees must have been prepared for winter by not fertilizing after June. This is the most important rule for Gulf Coast climates.

Passive cold abatement methods: First get the ground wet. Moist ground will allow heat to rise better than dry. Second, bare ground is needed. Don't listen to those telling you to use mulch. Tree canopies should just touch the ground on the outer edges to hold in heat. A 30 gallon garbage can full of water is a great passive heater for a one night cold snap.

The best investment is a heavy duty frost blanket. One layer will get you about 4 deg F protection, Maybe a tad more on a still night. I've seen this number quoted and have done the measurements myself. If your trees are hardened off, that will get you to 19 to 20 deg. For mainstream citrus that is usually enough.

"Banking" around trunks of established trees is great insurance.

If you use plastic tarps/sheets, try to use an internal frame,
since they conduct heat. Keep that air gap if possible.

Add a droplight and you are home free.

About using micro sprays and misting for freeze protection:
It sounds easy if you say it fast. I spent many years building and running small flow systems, and they fail at the most critical times. Searching the subject has confirmed my opinion. If you plan such a system build it early, test it, and retest it, and plan to be out there in the middle of a freezing night to see to keeps working correctly.

To clear up some confusion about using water/ice methods to keep 32 deg F. It only works when the water is in thermal equilibrium with the ice.

I have 32 trees in the ground. We had 18 deg F last night out at the Angleton, TX, airport. I have been working like crazy to gather all my fruit. I was most worried about my CCTC Kat mandarin. It has about 300 fruit on it and was not quite ready to pick. I will loose some leaves but my trees seemed better than I expected this afternoon. Time will tell.


    Bookmark   January 7, 2014 at 10:34PM
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Thanks Tantanman...I need to see about getting a mandarin. Some in the area say we just aren't far enough south for them. You are probably a little warmer there but probably not more than a few degrees.

    Bookmark   January 8, 2014 at 9:19AM
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Steve, Z (6Bground,5B roof) Cincy,OH

I had a cold snap to 7 F last year so I thought of spraying my fig trees. My Brother who is a chemist told me that ice on the twig would do much more damage because the dew poit was around 0-F. He said the ice would sablime to vapor and that it would take 80 units of heat to go to liquid and another 520 units of heat to go to vapor. This would guarantee death to my figs. I left them alone and lost about a third of that years growth.

Conclusion, If you spray, and the system stops mid-job you can do more damage. The heat of sublimation of ice to dry air is 7.5 time as great as the heat of fusion of water freezing to ice.

At -5F my fig trees died to the trunk banking of 3 FT of shredded leaves. I pays to have your systems ready in fall. This is the first year in 20 that I did.

johnorange I noticed you mentioned global warming. Be careful, I hear that can be a very hot topic.


This post was edited by poncirusguy on Wed, Jan 8, 14 at 10:36

    Bookmark   January 8, 2014 at 10:15AM
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