OK, I have no experience with this issue, but I was noticing leaves on a fig tree a few miles from my house, and they definitely show damage from cold weather, at a location that was probably below 32F. There was ice on puddles, but no frost because of the very low humidity.

Water freezes at 32F, but if you add salt, or other impurities, it will remain a liquid to an even lower temp. It seems clear that the water in a fig leaf is impure in that there are other chemicals in a leaf, which could lead one to conclude that a leaf should be able to stay unfrozen to some temperature less than 32F,

So, if I see leaf damage, limpness of leaves and actual dessicated patches on the leaves, at what temp did this happen? 32F? or something lower than 32F?

I'm not sure at exactly what temperature it will totally freeze, but at my place temperatures with 32° will not cause defoliation. We had temperatures below 30° that really did the damage. Usually the leaves will curl up and dry up. 

We had a forecast of 30F a few weeks ago, and it destroyed all of the new leaves on my in-ground BT.  all new foliage.  The old leaves were just fine.  New leaves were toasted. 

Here's the science behind your observations:

Frost damage and freeze damage are two entirely different mechanisms.  Frost can form on leaves at "air" temperatures that can be as high as 40 degrees F......it just depends on the air temperature, the relative humidity, and the atmospheric pressure whether or not frost will form.

LEAF "surface" temperature can be lower (as much as 8 degrees lower) than the "air" temperature due to evaporative cooling effects as moisture evaporates from the leaves. When the leaf temperature reaches 32 degrees frost (ice) will form ON THE SURFACE......causing damage to the leaf.

When the outside temperature was 32 degrees and you saw leaf damage but no obvious frost.....evaporation and cooling was still occurring on the leaves. Frost was most likely there in quantities that were not apparent to the naked eye. You likely would have seen it under magnification. There was just too little moisture in the air at that particular time for lots of visible frost to build up. 

Old leaves evaporate less moisture than younger leaves. Old leaves generally have a better weathered protective surface than younger leaves. Young leaves succumb to the cold much quicker than older leaves....because they are more "tender" and tend to produce more frost.


OTOH.....Freeze Damage occurs when the temperature of the internal fluids (sap) of the branches on a fig tree drops below its freezing point. The freezing point of tree sap depends on the amount of sugars & starches that are dissolved in the sap.  Let the sap freeze and it will expand in volume and can easily split open the channels that are carrying the sap. Sometimes when sap freezes (happens a lot in Louisiana because of our fluctuating temperatures) you can see large trunks or branches split wide open. Sometimes it appears as uplifted bark in some parts on the tree.

In the spring, sometimes I see that I have lost entire branches and not just branch tips to freezes that occurred at air temperatures that do not go below 25 degrees F for a couple of hours max exposure. That happens because between these freezes, the temperature will often rise to 60-70 degrees and start the internal flow of sap. This effect is murder on young trees in my area. It is much easier on fig trees if the temperature STAYS cold. Fig trees can handle steady cold......they go nuts with cycling up /down air temperatures. 

What determines the hardiness of a fig tree (in conjunction with heridity traits) is how much you have concentrated the sugars in the sap and thereby LOWERED its freezing point. You increase the dissolved sugar and starch content of the sap (which lowers its freezing point) by withholding water to your trees as they approach winter. You reduce tenderness by not fertilizing your trees late in the growing season. Also, you want to drive the sap DOWN into the roots and keeping it there. You do that by not stimulating your dormant tree with warming temperatures. Once they are dormant (most sap in roots) do not let them warm up too much again. Some varieties are real good at naturally concentrating the sugar and starch content of its sap and storing most of it in its root system during the winter.

Dan

Hi Dan,

I think my LSU Purple had some freeze damage way down low on its trunk because there are vertical splits in one place, however, it didn't kill the tree because it's about 4' tall now.  Is there anything I could put onto that area that would seal it, such as that black tree paint?  The splits are at the soil line and I'm concerned that the split area might rot out, or something could get into the bark at that point.

Thanks,

noss

I really don't know the answer to your question. I have been ignoring freeze damage and only prune dead branches in the spring.....too many to worry about.

Dan

Hi Noss,
i enjoy your posts .
My Ronde did split last winter down at the soil level 1 big crack and i used pruning seal that came in can with brush applicator, its black tar stuff.
Not to do anything else but to keep the bugs out .
I now use it on bigger limb cuts to seal with no harm so far.

Hi Martin,

Thanks for letting me know.  These cracks are down too low to prune and I'd have to cut the whole tree down to get rid of them.  The tree doesn't have any obvious problem from the cracks and the trunk gained some girth over the summer, so I wouldn't want to do any more than paint it and I'm glad you have done so with the paint.  I'll do that.  Didn't think to try and pare them off to fresh wood underneath and let that heal.

I had gone back to the nursery in early summer and the trees it had been with looked better than the one I had bought and I was disappointed, but I had also repotted my tree--twice--so it had sat and sulked awhile.  I didn't think my little tree was doing so great until I went back to the nursery where I got it, toward the end of the summer, and saw the LSU Purples they had left.  Those poor trees looked pitiful compared to mine.  That was a boost.

What was funny, was after I got the tree home and repotted it the second time, I was looking at it and noticed it didn't have a leader!  It went up so far and stopped.  I selected the strongest-looking of the branches and pulled it upright and tied that one to a sturdy stake and the tree was then twice as tall as it had been.  I think that really was the true top of the main trunk, but the tree was a whip and too thin to stand upright like it was supposed to.  Am getting to think fig trees are so forgiving to our foibles and for the newbies, our lack of experience. 

I'm glad you enjoy my posts--Thanks,  noss  ;)

Noss, I've seen pictures of your fig babies and saw that you are a very good fig mom.

Dan