John,

I think you are right about the wind funnel. There is a pretty big opening just behind the fence...

The last flush of satsuma (both leaves and twigs) are turning brown (yeah, brown select...) The older branches may be ok. I start noticing similar similar on grapefruit and orange leaves.

I also read it is a good practice to pick-up fallen leaves. I try to do it since my wife's roses produce huge amount of fungi on they leaves.

Thank you again!

Millet,

with my engineering background, I would suspect that wind will speed-up heat exchange making the plant to loose warmth more quickly but I may be totally wrong. Wind would certainly explain that spotty damage.

When a grape vine is killed or damaged by cold temperatures, the vine had long ago already dropped it leaves. Most winter damage to grapes occurs mid winter, or during a spring freeze when the vine has already begun to grow thus is very tender. As far as any tree dessication by wind, I believe it would take a longer time period then just during one night of an occasional wind that could damage one tree but not enough to bother neighboring trees. I agree that wind chill is only a factor with warm blooded creatures and not a factor for vegetation. - Millet (776-)

i agree that wind will speed-up heat exchange making the plant to loose warmth more quickly.

Like gdbanks writes wind can speed up the heat exchange, but does not cause the temperature to be lower (colder) than the ambient temperature surrounding the tree. There are a lot of additional reasons why one tree might be damaged while neighboring trees are unaffected. Was the tree stressed prior to the weather incident, are there freeze pockets, poorly drained soil areas, low spots, insect damaged, water stressed, sparse vegetation, and on and on and on. - (775-)

Millet,

thank you very much! I think you are absolutely right and what happened really was a combination of several factors. We enjoyed 83-85 (!) on Thursday, then got prolonged rain in early Friday followed by strong wind from the north and 29 F on Saturday morning... The freeze was not prolonged and lasted maybe 2-3 hours. Perhaps, the plant would have enough energy (heat) stored to withstand it if not wind. I may be totally wrong on this theory since don't really have experience, just understanding basic physics. Also, the plant had developed its most recent flush probably less than 2 months ago... Everything has summed up to produce that sad result.
Thank you again!

We've been dropping down into the mid to high 20's here at night lately. I'm surprised that there hasn't been as much frost damage. In 2007 with similar temps I had severe frost damage to my trees at my old house. My sour orange roostocks and USDA 88-2 liners seem no worse for wear. My Thomasville Citrangequat did just fine (Thanks to Ned after my 2007 freeze). I do have the trees up against a decomposing granite vertical hillside that sits in the sun all day. I wonder if radiational heating at night is keeping the plants warm. Maybe this is THE spot to keep my plants during the winter.

Phillip

Darkman,

this is exactly what I had in mind but failed to express!
I also remember an old physics demo of two glasses of hot water brought in a cool room. One glass was just in the room when the other had a fan blowing room temperature air across it. Both had thermometers in them. Water in the second glass had lower temperature than in the first one after the same time they spent in the room...

Thank you again!

Phillip,

this is great that your plants were not damaged! I am quite sure that the granite wall was an important factor.

When I was a kid many many years ago you could see large fans with airplane props all over southren Fla groves, in fact, you can still see some in Sebring. I can still remember my neighbors running the air boats thru the grove rows in the early morning hours to keep the air moving. Even now, in the mirco jet world,The USDA experimental lab near Port St Lucie has the top of an airboat mounted to a trailor so that they can move it around the grove. Although I know nothing about the trees, I live in an old abandoned grove, and not far from some very large working groves. Seems to me I have heard my father in law say, back in the day that you wanted to "blow the frost off the plants" so they ran the props at 32-29 degrees to keep the air moving and frost from "sticking" to the leaves. I'm sure the trees where in fact colder, but keeping te frost off saved more of the leaf. So if it was 30-32 for a short period the wind may have helped?

One strategy for low temperature avoidance is to heat the micro-climate around trees so they do not experience lethal temperatures. Wind machines were first used for freeze protection in California in the 1920s. Wind machines have been used successfully in recent years to combat winter injury to trees. Wind machines take advantage of the thermal gradient that exist over an orchard site during a radiational freeze. This technology is effective when the coldest air is situated at the ground near the trees. Air warms with height during a radiation freeze in what is called a thermal inversion. Wind machines blend air that is 20 to 60 feet above the ground with the air near the ground. The ability to warm air around the trees in a grove depends on the thermal inversion strength, which is defined as the diference in temperature between 6 feet and 60 feet above the ground. The maximum wind machine warming capability is estimated to be about 50 percent of the thermal inversion strength. For example, if the difference in temperature between 6 feet above the ground and 60 feet were 10F, then, under ideal conditions a wind maching could warm the air near the ground by 5F. A large wind machine can protect up to 10 to 12 acres. Currently the cost of these machines is about $20,000 to $25,000 per unit. (taken from "Winter Injury & Methods of Protection" - Michigan State University Extension. - Millet (774-)