So how cold did I really get?

[iwan]

I am having a hard time trusting the readings from my thermometer this last freeze. My low today was 21.9F and yesterday was 23.1 with 12+ hours below freezing both days, but the plant damage doesn't seem to correspond. The remote sensor is at 5' under a small tree and above lawn. My rural temps average 3-5 degrees below official airport readings (also fairly rural, but probably some heat island effect there). During the big freeze of 2007 I referenced this digital thermometer with a traceable thermometer in our cold room at work in the range of 36-39F. The sensor was actually reading .8 degrees higher than the traceable thermometer, which actually makes my measured temps almost a degree lower. The sensor has a small solar shield, but is not in a shelter or aspirated.

The damage I am seeing appears more in line with a 26-28F freeze (official temps were 27F and 28F). For example, the week prior to the freeze I was recording daily lows in the 28-32 degree range, yet fruiting bananas were only spotted or undamaged.

So based on the following what was my probable temps? Temps are my estimates where damage occurs).

Fruiting bananas foliage toast (32F), but pseudostems not collapsed (>28F)

Exposed Canna foliage toast, but solid stems. Canna under canopy somewhat burned (~28F)

Alocasias defoliated or melted to ground depending on species (30-32F)

Exposed Archontophoenix cunninghamiana foliage bronzed/burned, but not collapsed (27-28F)

unknown Lilly (Crinum?) wilted (26-28F). Turned to mush in 2007

Philodendron selloum under loose canopy undamaged (damaged below 26F?)

Alpinia zerumbet burned (exposed), some damage (under canopy) (28F)

Jacaranda mimosafolia foliage bronzed (28-30F)

Agapanthus wilted

Manihot esculenta defoliated

Livistona chinensis (under canopy) undamaged

Rhapis excelsa (under canopy) undamaged

Phoenix reclinata (fully exposed) undamaged

Phoenix reclinata x roebelenii (fully exposed) undamaged

Beccariophoenix alfredii (tented by heavy blanket but exposed on sides), undamaged

Ravenea rivularis (tented by heavy blanket but exposed on sides), undamaged. Part of frond exposed, some blotching (~25F)

Syagrus oleracea no apparent foliage damage (fully exposed) but had rope lights on "trunk" (surprising)

Now to throw a wrench in things, the insulated water supply line from the well froze yesterday (~50% restriction), and almost completely froze this morning, even with a trickle of water left on all night.

I know some of the palm damage may not show up for a week or two (or even until summer heat arrives), but damage is nowhere near what I would expect for low 20 degree temps. So let's hear from you weather observers/experts out there. I would love to be able to know my readings are reasonably accurate +- 1 degree.

[PalmGuyWC]

Hi Robert,

It's nice to see you back on the forum. Long time, no see. I also don't trust my temp. readings. I have two remote sensors, one in my front and one in the back, both several feet above the ground. Placed side by side the sensors agree within one degree, but placed in different locations there is as much as 5 degrees variance.

My lowest low from the recent freeze showed 27 Degrees, but judging from the cold sensitive plants, and the extense of the frost, it seemed lower. The top half inch of my ground was frozen and I had ice in my rain buckets. My alocasias turned to mush the first night and all the cannas turned black, even the ones under canopy. I also use Lantana as gage plant. When they are killed back, I know it's been down to 25F. As you said, it will probably take several weeks to see the extent of the damage, but this was a nasty little freeze. I just hope my Parajubaea TVT didn't get burned. It was glazed wilth white frost. In the '07 freeze it took several weeks before the damage showed on the Parajubaea.

Dick

[Tyrone]

C renda, dead at 60F.

[iwan]

C renda, dead at 60F.

Tyrone, that would have died from cold in my house.

Dick,

I was pretty much prepared for the cold except I did not get a chance to cover some palms, to keep them dry more than from cold. With a few exceptions, I don't stress too much if temps stay above 25F. I have a few "special" palms in the ground that I take efforts to protect.

Archontophoenix cunninghamiana gets burned every year and defoliated every few years, but recovers nicely with rope lights and protection. It is now too tall to provide easy overhead protection until the queens grow up to provide canopy. Planted in 2005, it survived the freeze of 2007 with protection.

1g Copernicia prunifera that was planted in spring. Covered with a 15g pot and blanket. Should be hardy (except for a record freeze) once established.

A weak strap leaf Butia x Parajubaea that has never really grown since I got it. It looked undamaged yesterday morning.

A couple of trunking Phoenix roebelenii doubles that I transplanted from Dave's place two years ago. Three of the trunks had finally recovered from being transplanted and moved to the desert heat, but the fourth is still iffy. Protected with rope lights and tarp to keep frost off.

There is also a Syagrus, probably Syagrus picrophylla or x-Costae (couldn't find the label in the dark under lantana). It appears undamaged with only a couple loose wraps of rope light and under the tarp covering the roebelenii.

Syagrus oleracea is a surprise so far, showing no foliar damage with just rope lights on the "trunk" and no overhead canopy. It was planted from 15g in spring and really took off in the ground.

Beccariophoenix alfredii (1g) planted in spring

Ravenea rivularis (5g)

The only other palm I am concerned about is a weak Dypsis decipiens that was planted a couple years ago. I forgot to cover it to keep it dry then it got frozen while soaking wet. Normally, I wouldn't have planted this in fall, but I have lost all my potted decipiens, so I figured, it had a better chance in the ground.

All the babies and wimps are in the garage.

We were spared a third day of serious freeze. Last night my thermometer recorded 29F at 9PM, but clouds from the next storm rolled in and it was 33F at midnight and 36F approaching sunrise.

[BS Man about Palms]

Hi Robert.

As Dick alluded to, comparison is often the key. Preferably you have 3 sensors or more. IF you placed them all together for several hours undisturbed, they should roughly match. Maybe buy 2 new ones and see if they agree. Once moved apart, if they are different, you have different temps. My back yard is almost consistently 2f lower than my front yard.

That being said, a lower temp with less humidity will often bring less damage than a higher temp with higher humidity. Something about freezing the water in the cells. I believe thats why Florida guys have severe damage when its 32-34F versus us in the 20's. Learned a bunch back in Jan 2007.

[iwan]

Bill, I would love to throw this in an official NWS weather shelter for comparison, but I have tested it against a calibrated lab thermometer at work. I couldn't do an ice water check since my sensor is not submersible. I was not able to convince the lab manager to let me take their thermometer home to test it in my freezer. Indoor comparisons to my thermostat temps are within a few tenths.

I am sure it is a yard level microclimate/measurement issue, but what has always confused me are all the requirements for "official" temperature recording. My plants are not in a weather shelter at 5' above a lawn with aspiration. They are (for the most part) exposed to the sky, and even at ground level (which would be colder).

Hi Robert.

As Dick alluded to, comparison is often the key. Preferably you have 3 sensors or more. IF you placed them all together for several hours undisturbed, they should roughly match. Maybe buy 2 new ones and see if they agree. Once moved apart, if they are different, you have different temps. My back yard is almost consistently 2f lower than my front yard.

That being said, a lower temp with less humidity will often bring less damage than a higher temp with higher humidity. Something about freezing the water in the cells. I believe thats why Florida guys have severe damage when its 32-34F versus us in the 20's. Learned a bunch back in Jan 2007.

[Matt in SD]

Hi Robert,

If your sensors are exposed to the sky, that's the reason your readings seem so low. You'll get radiative cooling of your sensor on calm, clear nights, and therefore won't actually be recording the air temperature. The reading you get on an exposed thermometer on a calm clear night is pretty meaningless, similar to a thermometer in the sun during the day. I wouldn't be surised if you could get readings 10F below the actual air temp.

Try putting it under a tree, or putting some sort of cover over it. There are some way more knowledgeable guys on here than can maybe give you simple ideas for getting more meaningful low temp reading.

Matt

[MattyB]

He said it was under a tree Matt. Why don't you try reading the rule book shankapotomus.

Now that I'm done chastising Matt...... Robert, if the tree is small and the sensor can still see the sky at an angle, you'll still get a false reading. You're probably smarter than me about that stuff though. Does this tree have any leaves on it or is it a Charlie Brown Christmas? I do know that A. cunninghamiana only suffered very minor spotting at three nights of 24F, 27F, 28F at my place in '07, so for that species at least I think you're expectation of damage was off.

Also, I've sealed my sensors in zip lock baggies and submerged them in ice water. Seems to work. I even did the home base sensor to test it. I think I got it to read 33F or 34F at the most which I probably just about right.

[doubravsky]

Shankapotomus...... are you getting vocabulary from talking tv commercial babies again?

He said it was under a tree Matt. Why don't you try reading the rule book shankapotomus.

Now that I'm done chastising Matt...... Robert, if the tree is small and the sensor can still see the sky at an angle, you'll still get a false reading. You're probably smarter than me about that stuff though. Does this tree have any leaves on it or is it a Charlie Brown Christmas? I do know that A. cunninghamiana only suffered very minor spotting at three nights of 24F, 27F, 28F at my place in '07, so for that species at least I think you're expectation of damage was off.

Also, I've sealed my sensors in zip lock baggies and submerged them in ice water. Seems to work. I even did the home base sensor to test it. I think I got it to read 33F or 34F at the most which I probably just about right.

[iwan]

Matty, it is under a small evergreen tree, there isn't a broad canopy, so you might have something. The damage is starting to show up on the palms. Got some daylight time today and pulled the blankets off before the rain, so did some inspection.

Ravenea has dark patches, B. alfredii showing some discoloration but still looks pretty good, Chamaedorea cataractum is black where it touched the blanket covering it, Dypsis onilhensis similar but had rope lights, blanket and a tarp. Dypsis decipiens showing damage. The backyard smells like a homeless shelter, which is strange because usually freeze damage smells like old boiled spinach to me.

After each winter I keep saying I am going to build an "official" weather shelter, but work and other activities usually take higher priority.

If I was only (in reality) in the 25-27F range then I had more damage than expected. My Jacaranda looks like a Chocolate Silk tree, but a couple in town show no damage with the obvious heat island effect. My A. cunninghamiana always burns if exposed when the airport temps hit 27F, 24F when I was able to cover it.

SD Matt, enjoying your new place?

He said it was under a tree Matt.

Now that I'm done chastising Matt...... Robert, if the tree is small and the sensor can still see the sky at an angle, you'll still get a false reading.

[MattyB]

Robert,

For weather protection I always take a tupperware container, and screw it to the tree like a rain cover, to cover up my sensor so it dosen't get wet. This should solve the problem of the sensor 'seeing' the sky

[paulgila]

matt yer wife HAS been wondering where all the tupperware is going.

dont ask me how i know.

[MattyB]

speaking of cold

[paulgila]

[DoomsDave]

This is an excellent question, snarkedelica aside . . . .

Oleanders freeze at 18F, Phoenix reclinatas at 20 F.

Exact temps will vary all over the place in a given yard. If your sensor is on even slightly higher ground viz-a-viz a nearby frozen plant that can produce some confounding readings, in the light of what got killed.

[iwan]

Phoenix reclinatas at 20 F.

Exact temps will vary all over the place in a given yard. If your sensor is on even slightly higher ground viz-a-viz a nearby frozen plant that can produce some confounding readings, in the light of what got killed.

Got a chance to check out the damage some more during the daylight today. I am beginning to think my readings may not be too far off after all, or that the freezing of wet foliage mimics damage indicative of colder temps

I have two Phoenix reclinata that Dave gave me last year. Both were 15g. One is planted in a low spot in my front yard next to a drainage ditch, it is significantly yellow in color after the freeze. A Phoenix reclinata x roebelenii 10' away shows little to no damage. Both fully exposed. The second reclinata in the back yard is still in a 15g pot and crowded amongst other potted palms in my back yard, shows little to no damage.

Sabal yapa (1g) substantially burned, fully exposed

Chamaedora microspadix, in ground two years, under canopy, looks pale

Chamaedora radicalis (three in 2-5g pots) some discoloration/spotting

Ravenea rivularis showing more damage

Becarriophoenix alfredii no change, some discoloration, spotting.

unknown Agave (5g) some damage. Was defoliated (is that appropriate for Agave?) in 2007, but recovered

Rhapis humilis planted and potted, under canopy near Rhapis, undamaged

Syagrus oleracea still shows little or know damage

Cordyline indivisa (5g), discolored. Cordyline australis undamaged

Coreopsis gigantea (10g) under 20% canopy. Undamaged. Supposedly hardy to 25F. Surprised I haven't killed this in two years of summer heat.

Other palms look pretty much the same.

[iwan]

Now that normal spring weather has finally arrived, it is time to survey the damage. In spite of the December freeze, this was one of the mildest winters/springs in years. Record persistent late spring rains and low monthly average temps for April and May. We just hit 90F for the first time last week and had only a handful of low 80's. This proved too much for some hardy palms and produced a few surprises.

Most bananas killed to the ground and have yet to sprout from the roots.

Alocasia/Colocasia killed to the ground and have yet to sprout from the roots.

Exposed Archontophoenix cunninghamiana foliage bronzed/burned, recovering nicely. Rope lights on trunk during freeze. 70% defoliated.

Jacaranda mimosafolia (two) killed to the roots. Resprouting from the roots.

Manihot esculenta defoliated. Lost about a foot of tip, minimal damage.

Livistona chinensis (under canopy) undamaged

Rhapis excelsa (under canopy) undamaged

Phoenix reclinata (fully exposed) 80%+ defoliated. 10' away from reclinata x roebelenii below.

Phoenix reclinata x roebelenii (fully exposed) minor foliage damage. Ray Laub hybrid. Survived 2007 freeze in a 2G pot (spear pull). Promising.

Beccariophoenix alfredii (tented by heavy blanket but exposed on sides), 50% frond burn. Pushing new spear. Planted spring 09 from 1G.

Ravenea rivularis (tented by heavy blanket but exposed on sides). 100% defoliated. Pushing new spears

Syagrus oleracea 20-25% burned (fully exposed) but had rope lights on "trunk" (surprising)

(Jubaea chilensis x Butia capitata) x S. romanzoffiana (unprotected). Spear pulled, but recovering. Planted 3/09 from 2G tree pot.

Brahea clara, spear pulled, but recovering. Planted 11/1/09 from 15G (another one 200' away undamaged).

Jubaea chilensis, spear pulled, but recovering. Planted 9/09 from 5G.

Washingtonia some bronzing on 5G size volunteers.

Syagrus romanzoffiana (various), showed burning similar or slightly worse than Syagrus oleracea.

Various 5G potted Livistona (decipiens, nitida, australis) 50-100% defoliated.

Various potted cocoid hybrids, no damage or minimal spotting max.

Probably some other damage on smaller potted palms that I haven't found in the weeds.

There has been very little heat to push new growth or allow fertilizing, so everything looks pretty much like it did in February (except for Archontophoenix cunninghamiana which is loving the cool, wet weather.