MrTexas,

thank you very much for your suggestion!

Yes, I do have small banks of dirt in addition to pipe insulators. Also, that plastic covers the entire plant from the ground to the top and is enclosed. I will reserve the light bulb method for really cold nights as an emergency measure.

Regarding the temperature, it is something about our spot. We are usually 3-4 degrees below the forecast although I'm just 3-4 miles north from you!

Let's hope...

Thank you again!

I have to agree with Mr. Texas. Foam pipe insulation is a good insulator for something than generates heat or has a high heat capacity but the tree trunk doesn't have either of those characteristics. Banking soil allows heat to be conducted from the ground below in addition to insulating the tree. Also the water content of the soil, in addition to increasing the heat capacity of the soil, prevents the soil from dropping below freezing until the large amount of energy needed to freeze water has been lost from the soil.

Jrb,

Thank you very much! That makes perfect sence! I will modify my protective measures.

ivica,

very interesting statistics! Despite what the airport says, the thermometer on my house wall read -8.9 C one night and -8 the other...

Another factor that made a difference would be snow that actually protects plants keeping them warmer than the surrounding air. I think this is why your plant died above the snow level. Last year, we did not have snow, which made it harder on plants.

Thank you!

I spoke with the University of Florida staff at their Live Oak farm where they grow Owari on Swingle and Trifoliate rootstock. Last Winter they had lows of 14.7 and many (over 30) days of below freezing. They used no protection and had no tree deaths. They said they experienced 20% - 30% leaf loss and nothing else. They said that the Swingle provided better protection than Trifoliate.

Tonight I met with a man who has 67 Owari and Brown Select Satsumas that are all on Trifoliate. He uses no protection and had no tree loss last winter. His trees are north of me and will generally be 5 - 9 degrees colder than me. My lows last winter were 19.5. He has ordered 150 more trees for this spring.

I have call in to U of FL Quincy farm to inquire about their trials but I have not heard back from them.

I'm not sure what all this means but it is more information to confuse my mind.

Here is a link to Florida weather stations that are accurate and you can download historical data. Anyone researching how weather effects cold hardiness will find these sites valuable. They have soil temps too.

http://fawn.ifas.ufl.edu/

Check it out

Darkman,
thanks for the link.
Here is the link which could be, I hope, useful to mandarine grovers out there if they want to compare their local weather conditions with conditions in our mandarine area (lower valley of Neretva river, nearby towns Metkovic, Opuzen, Ploce):
http://pljusak.com/
Station is "VID":
http://pljusak.com/vid/wx.htm
Only one station in that area publicaly available for now.
To locate VID station start from Adriatic Sea and border of Croatia and BiH following Neretva river. Google Translation works OK.

Each time I take this road going to Kosovo or Albania I stop by the lakes of Baćinska north of Ploče. A very nice place. I also flown over this region in PPG (paramotor) taking off from the harbour of Ploče. It was fabulous.

A little off-topic.

Randy,

Thank you very much! Yes, i understand that my gauge may (and most likely will) read slightly higher temp than it should... The difference in 1-2 degrees is not that bad, is it? What I am saying is that despite it's location, the readings i see are lover than the forecast... I trust my gauge better.

No, not bad at all. I recently installed a weather station. From the software you can get some good information I have on my weather station web site. Kind of neat.

http://mybaxleyweather.localweatherview.net

Randy,

that's really great! I should get one too.
Thank you for the advise!!

Here is the update on the current situation:

The plant lost some leaves and the last growth seem to be dying back, which should be ok...

The only thing concerning me is that one branch developed a crack in the bark that seems quite deep. Here is a picture of it:


Could this crack be due to a frost damage?
I covered it by a black pruning sealer for now...

Thank you!

Yes, crack is from freeze damage. You don't have to do anything to it. It will heal on it's own in the spring.

The wound would have healed better if you had not covered it with the black sealer. When a citrus tree is pruned sealer should not be used. - Millet (746-)