I’m really surprised you might get a total loss of apple buds. I’m not too far away in NE Ohio and don’t expect that, but I admit I haven’t kept close watch on temps and buds this year. Did you get apples last year?
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I get it. I mean no disrespect. Some of it doesn’t make sense. Just that in my research, frost often causes expansion and damage to plant cell tissue. Then when it melts an endothermic (strips latent heat from the plant) reaction takes place, superchilling and already damaged bud. This is actually worst when a hard frost is quickly melted by strong morning sun, sometimes when ambient temps may actually still be below freezing. This is exactly what happened several days ago. My temps were not cold enough to kill apples or peach buds according to those critical temp charts, yet every tree I didn’t have protection on had major damage. I haven’t ran any scientific experiments (I teach science), but pretty much all of my anecdotal experience matches what I’ve found.
To be clear, I’m sure those critical temp charts are accurate, which is why I suffered no damage at colder temps without frost. However, I feel they are flawed when coupled with frost. I also think there are a huge host of variables that can attribute to no damage vs some-lots of damage for cold or frost. One being the amount of water/soil saturation and plant cell moisture. The research indicates higher cell moisture intensifies cold and/or frost damage at higher temps. That always seems to be the case for me. Big cold front drops tons of precip and then plummets temps on the back end.
But hey, I’m not dogmatic. I could be totally wrong and just have some weird coincidental affects. This just seems to be what happens to me every year. I would love to know for sure, cause at the end if the day all I want is fruit!
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We did get some apples. About 50 from the same tree (honeycrisp) that has the worst loss this time around. A fuji and Granny are the other two old enough to fruit. Those two lost everything last year to frost during full bloom.
We haven’t lost everything yet. Each tree has something left. Maybe I’m being pessimistic. But with loss already, bloom coming soon and more frosty nights in the forecast, I’m worried. Hoping those nights trend warmer than colder, but that’s not normally how it seems to go. Probably should take note of my own moniker and pray a little more vs complain about it. 
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Apples aren’t the easiest to tell when the buds/flowers/fruitlets have been damaged. Stone fruits are easier. I can tell when those are damaged soon after the fruit thaws out.
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True. I’ve been cutting them open to verify. The day after the cold I could find no damage in ten buds/tree on any of the trees (I’m sure there was some). The day after the hard frost 8 out of 10 buds were goners on the honeycrisp, a little lesser so on the other two. I do remember Olpea talking about the affect of concurrent nights of cold increasing likelihood of damage.
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Here’s a great article on all of this. One note is that those critical temps were only relative to 30 minutes of exposure. Most of the time I see lows bottom out for several hours before sunrise.
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The terminology in the PSU article isn’t the best. They say frost when they mean freeze. The title should be Freeze, Critical Temperatures, and Freeze Protection. Frost has two common meanings in this context. I think the term frost should be saved for the form of frozen dew that forms on objects. Fruit buds don’t suffer frost damage, they suffer freeze damage.
The question of whether frozen dew, frost, causes damage above and beyond freezing temperatures is a separate discussion.
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Actually, I’m going to side with Faithful on this very engaging discussion. Frost is more damaging than just temperature to blossoms.
Kocide 3000 is labeled for use to prevent frost on blooms, by killing ice nucleating bacteria. It turns out water can sometimes be super cooled if there isn’t anything for the water to start to crystalize on (like ice nucleating bacteria).
Therefore, the temps can get down to something like 27 degrees and the water won’t freeze (I know water can be super cooled to much lower temps in the atmosphere, but not on blossoms). But preventing ice forming on the blossoms (i.e. frost) it prevents damage to the flower.
I’ve used copper before for the purpose, but it still formed frost when I tried it. It’s been quite a while since I’ve read about it, but I believe the frost increases desiccation of the flower, vs the small amount of super cooled water dew on the flower.
Now if the air is so dry frost won’t form, I don’t know if that’s more desiccating than frost itself. But if there is some humidity in the air, it’s best not to have it freeze on the flowers.
Ironically, water sprinklers are actually a mitigation procedure to minimize damage to blooms. In that case, as the water freezes it gives off enough heat to warm the flowers up. Fruit specialists do recommend to keep the sprinklers on well after the ambient air temperature hits 32F, as the reverse happens as the ice melts.
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The amount of heat gained and lost around a flower due to latent heat of fusion is relatively small. Maybe it makes a difference near critical levels, but I think the debate here is frostless mid 20s and colder being better than frost with temps closer to freezing. That is what I can’t wrap my mind around.
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I’ll have to think about the desiccation some more and how that can relate to snowflake microphysics since both involve deposition. The difference here is the flower is acting as the condensation nuclei versus a speck of dust or some other particle in the atmosphere.
You have supercooled water droplets in the cloud that deposit moisture on the nuclei (we call them cloud condensation nuclei (CCN)) and you end up with a small ice crystal. It grows via differences between the vapor pressures of ice and that of water. Water has a higher saturation vapor pressure than ice at the same temperature so it will readily lose its molecules to it and the ice crystal grows…ie a growing snowflake. So I wonder if that relates to the desiccation of the flower. The water in the plant cells becomes attracted to the now forming ice crystals on the plant.
Like I said before, I can talk meteorology all day and I enjoy trying to incorporate it into growing things, but when it gets to the plant cellular level it goes out of my pay grade.
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Good luck this year. I did a quick survey of my apples and it looks like some were open enough to be toast like Hudson’s Golden Gem), but varieties like Liberty, Black Oxford, a couple of the Limbertwigs are still pretty tight so I’m optimistic. We had a low of 24°F this past week followed by 25°.
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Check this article from Penn State:
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