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Old 03-03-2018, 07:50 PM
 
Location: S.W. British Columbia
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Quote:
Originally Posted by Cambium View Post
More clear days than cloudy as usual with a strong Arctic blast but you need to factor in sun angle at certain latitudes. It's not the UV that kills the landscape in winter but I'd like to see if there's been studies on that.


Keep in mind my daytime temps went into the 20s and that wont burn the leaves. 4 of the 14 days did stay in the teens during the day. It was the frigid winds and nighttime temps mostly

And I don't think there are ice crystals when the air is bone dry. I could be wrong but many times the dewpoints aloft were super dry like -30C(-22F).

Take a look at my Holly 2015 picture on the left. A deep snowpack that winter preserved the holly tree on the bottom while getting burnt with the Feb 2015 Arctic consistency... Pure indication that the cold air + WINDS kills it, not the snow.

Poor holly tree. I remember you posting about that after it happened. Yes, deep cold and wind can cause Winter Dessication of evergreens, the most susceptible ones being the broadleaved ones like holly and mahonia because their leaves have more surface area to lose moisture from and the moisture isn't being replaced. In hollies it's called Winter Holly Scorch (or at least that's what we call it up here). The snow does act as a protective insulator wherever it covers the foliage. If you look at the picture in the link below (about what causes winter dessication) you'll see the trees where the same thing happened to them as what happened to your holly. Where the bottom parts of the trees had been covered in snow they were insulated and protected from losing moisture and stayed green, but on the tree parts above the snow where they had been exposed to cold and wind they became dessicated.

https://www.gardeningknowhow.com/pla...-in-plants.htm


Re: ice crystals and magnified UV burn you are probably right that it's not the problem with your holly and it looks to me like common winter dessication. Maybe you are not far enough north for atmospheric ice crystals to be as prevalent a problem as it can be further north. And I doubt it ever happens in the deep south. In the north, even in the arid interior when the air is bone dry there are still so many ice crystals in the upper atmosphere refracting and magnifying UV rays that it does cause risk of UV burn to northern evergreens (as well as animals). And if there is even a hint of moisture in the air, or snow or sugar ice covering the ground, or expanses of reflective water on the ground that also increases the amount of ice crystals in the air closer to the ground. Then on very clear sunny days there is a huge, blindingly brilliant corona around the sun and the air everywhere in all directions sparkles from sun up to sun down with flashes of UV light, like fireflies flying around you. The flashes are tiny but bright and piercing like the UV light sparks that come from a welding torch only in this case it's the sun's UV light being refracted and magnified every which way by the ice crystals in the air. The UV burn (and consequent drying) from that reflected light on exposed animal and plant tissue can be as damaging as the burn one can get in the desert in high summer ...... not to mention the debilitating "snow blindness" that is caused from the UV burn on the corneas of the eyes of animals and humans if they're exposed to it for too long. It's hard to avoid it because it's coming at you from all directions, even from the ground.

.

Last edited by Zoisite; 03-03-2018 at 07:59 PM..
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Old 03-04-2018, 10:31 AM
 
Location: North Idaho
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Don't know yet. I've still got at least 8 inches of snow on the ground. The pine trees are fine, everything else is still buried.
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Old 03-04-2018, 03:51 PM
 
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Drove by my old house in Tampa today and i had planted a coconut around 1999. Tree was full grown and looked dead from the last freeze this last Jan.
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Old 03-04-2018, 09:41 PM
 
Location: Heart of Dixie
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Quote:
Originally Posted by Zoisite View Post
...the air everywhere in all directions sparkles from sun up to sun down with flashes of UV light, like fireflies flying around you. The flashes are tiny but bright and piercing like the UV light sparks that come from a welding torch only in this case it's the sun's UV light being refracted and magnified every which way by the ice crystals in the air...
It seems you are unaware of the fact that UV light isn't visible to the human eye.
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Old 03-05-2018, 03:21 AM
 
Location: S.W. British Columbia
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Quote:
Originally Posted by Dirt Grinder View Post
It seems you are unaware of the fact that UV light isn't visible to the human eye.

No, I'm aware, and thank you, you are right to correct me on my bad terminology and misuse of the term "UV light". But the sunlight is visible and UV is in sunlight. I should have used the words "UV radiation" or "UV in sunlight" instead of saying "UV light". Otherwise it could confuse people who read things out of context and take things too literally, or who are looking for things to be hecklers about. It's a lazy habit of mine to say UV light or IR light, it comes from referring to the overhead ultra violet or infra red lights in the greenhouses and hatcheries, you know, the kind of lights you plug in and turn on with a switch.

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Old 03-05-2018, 02:15 PM
 
Location: Heart of Dixie
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Quote:
Originally Posted by Zoisite View Post
...Otherwise it could confuse people who read things out of context and take things too literally, or who are looking for things to be hecklers about...
I didn't read anything "out of context". You made the statement "...flashes of UV light, like fireflies flying around you. The flashes are tiny but bright and piercing like the UV light sparks that come from a welding torch..." Well, sorry, but that's just not accurate. You make an obvious mistake and your recourse is to label me a "heckler". Get your facts straight before you lay the blame on others.

I'm fully aware of the reflective nature of snow and ice increasing UV radiation exposure. In fact, the reflection of UV radiation from snow and ice is the primary cause of photokeratitis.
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Old 03-05-2018, 03:56 PM
 
Location: S.W. British Columbia
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Quote:
Originally Posted by Dirt Grinder View Post

...... I'm fully aware of the reflective nature of snow and ice increasing UV radiation exposure. .

If that's the case then can you please explain why you asked me the following question with reference to what you now say you were already fully aware of? I already requested of you once before to explain your question and you ignored my request. I'm sure you must have had a reason for asking:
Quote:
Originally Posted by Dirt Grinder View Post

Where's the source for that one?




Quote:
Originally Posted by Dirt Grinder View Post

..... In fact, the reflection of UV radiation from snow and ice is the primary cause of photokeratitis.
Yes, I had already explained in my previous post that the reflection of UV radiation from snow and ice causes snow blindness (photokeratitis). There are also several other ways the same corneal damage can occur from artificially produced UV radiation: Ultraviolet Keratitis


And here is some information about some of the ways in which ultraviolet radiation can damage plants.

https://www.quora.com/How-does-UV-ra...esis-in-plants

https://www.gardenguides.com/132133-...let-light.html

.
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Old 03-05-2018, 03:59 PM
 
Location: S.W. British Columbia
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Isleofpalms85, I'm sorry your thread got hijacked.


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Old 03-05-2018, 04:35 PM
 
Location: Heart of Dixie
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Quote:
Originally Posted by Zoisite View Post
Isleofpalms85, I'm sorry your thread got hijacked. .
Yep. People shouldn't post false information.
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Old 03-05-2018, 04:48 PM
Status: "..............." (set 4 days ago)
 
Location: 46060, Hardiness zone 5b/6a
2,097 posts, read 1,509,527 times
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In Central Indiana, I have noted that a Nellie Stevens Holly has been >80% defoliated, and probably also has some dead branches( I won’t know the exact severity of winter injury on this Holly bush until probably mid April, when it refoliates or starts producing new leaves), two southern magnolia trees(Brackens Brown Beauty Cultivar), the Southern Magnolias have about 50 to 75% foliage bronzing(sun burn or browned out leaves due to frozen soil, intense cold and winter sun), many other Evergreen shrubs have at least some leaf burn/needle burn for similar reasons. Crape myrtle(Died), Leyland cypresses are all toast, as are other species of trees or shrubs usually not seen this far north(at least not this far north in the Midwest). It remains to be determined whether the Southern Magnolia saplings that I have referenced above in my post have any dead branches or branch dieback from this winter’s unusually cold temperatures( I won’t know this until probably late May, when they start producing new branches, leaves and flowers).
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