How Does Frost Damage Leaves

[DrTolhur]

It's generally common knowledge that frost at the edge of a season can cause harm to trees/leaves, but I've never seen anyone talk about how/why that happens...what the mechanism is. Is it literally the frost itself (the thin layer of ice crystals on the surface of the leaf) or just the cold temperature? I'm hoping for an actual physiological explanation more than hypotheses or even experiential observations.

 

[Colorado]

I am no scientist, but I believe damage occurs at the cellular level. Under certain conditions, water crystallizes, expands, and causes damage to the plant tissue.

Someone else will have to chime in with a more detailed/accurate explanation

 

[DrTolhur]

Yeah, the damage is certainly in the cells. I assume it's basically the same as frostbite for humans, where the water inside the cells freezes and kills the cells/tissue. But there's enough dissolved stuff inside the cell water that I would think it would freeze well below 32ºF. So maybe it's the water condensing on the outside of the leaf surface that then expands and creates sharp crystals that puncture the cells from the outside in. This is what I'm hoping someone with specific knowledge can answer.

 

[Wires_Guy_wires]

When foliage has just started growing, it's not yet producing enough sugars to resist ice crystal formation. Because the foliage is burning more than it's producing.
Add to that the fact that the cuticle is still forming so things can pass more freely through the leaf itself instead of bouncing off of a wax shield.
The more water, the harder the freeze burn.

In spring time, most plants don't produce the chemicals that reduce freezing effects, like glycerole and sugars. They use those instead to fuel growth. In general, this effect is stronger in deciduous plants.

A layer of water on the outside however, seems to have a protective effect for some reason. I don't know the exact mechanism but I think it has to do with the way water freezes and how it has to lose heat to become ice. Without solutes, it's a lengthy process to lower the temperature of water below 0°C. A thin film of ice is also a poor conductor of energy so cooling something through a sheet of ice is difficult.
You can try this effect yourself by putting a bottle of water in the fridge for a day, then boil some water. Pour the two in a glass and when you drink it right away, you can actually feel how hot and cold water don't mix themselves.

 

[DrTolhur]

Wires_Guy_wires, can you consolidate that into what you're suggesting is actually happening, then? It sounds like you're saying the water inside the leaves doesn't have enough solutes to significantly lower the freezing temperature (when they're young), so that water is able to freeze, which would kill the cells. However, that would happen based on ambient temperature alone, without regard for frost. So does the actual frost play a part, here, or just temperature?

 

[Wires_Guy_wires]

I'm not sure that I get what you're asking so feel free to clarify!
It's just temperature that can cause frost burn, zero degrees C is usually not an issue due to the solutes that lower the freezing point a little. A little lower usually isn't either but it's dangerously thin ice. But dropping to -5°C will ruin plant tissue if it doesn't contain some kind of natural antifreeze.

To me, frost is when ambient outdoor temps drop to or below the freezing point of regular water. Ice formation isn't part of that definition to me.

Ice crystals usually don't get inside a leaf, but the mechanical forces of a layer of ice can break tissue open, causing them to leak. If they leak, they lose solutes and as a result ice can get in as well (or water inside the foliage can freeze, depending on how you look at it). If the ice melts rapidly, the plant can still get damaged because its own processes for recovery require a certain temperature to function properly, usually a plant then necrosizes - I forgot the actual term but it's abscission combined with organised cell death; necrosis - the damages part and shuts it off.

 

[DrTolhur]

Frost is the actual layer of ice that forms as moisture in the air condenses onto a surface due to falling temperature and freezes. Air temperature going below freezing does not always lead to frost. For example, if you park outside, you don't necessarily have to scrape your car windshield every day...only when frost forms.

Some of what you said is a little confusing. In your first paragraph, you talk about the tissue needing antifreeze, suggesting that the water in the cells will freeze. In your last paragraph, you said that ice doesn't usually get into the leaf, but can cause damage from the outside (i.e. frost on the leaf). And this is my question: is the damage caused by frost (i.e. the actual ice forming on the surface of the leaf) on the outside or freezing of cellular content internally?

 

[Wires_Guy_wires]

Thanks for the clarification.
In my language frost just means freezing temperatures. We call the actual frozen dew 'ripe'.

Ice from the outside doesn't enter the leaf unless there's damage (mechanical damge from the outside ice, or from ice crystals on the inside).
Water inside the leaf can freeze and form crystals that damage it, if there are no antifreeze agents present.

The damage can be from both, but in general the most damage is done by the water inside the leaf that forms crystals and not from the freezing dew that penetrates the leaf from the outside. Unless of course.. The temperatures drop so low that the foliage loses its flexibility and ice from the outside "blooms" in crystalline form so that it punctures everything in its path, but that's mechanical too.

 

[AlainK]

Frost damages leaves. But how will some species respond? That is to me the point.

I've had maples or Chinese quince (Pseudocydonia sinensis) whose leaves were totally destroyed by the frost, yet, new leaves pushed out when the weather got milder, to no harm to the trees. There must have been enough sugars in the wood and the roots. But here, -10° C (14 F) after leafing out is exceptional and doesn't last for more than a couple of days. Some species can probably suffer more from a late freeze, I don't know.

About the "mechanism" inside the leaves, I don't know either : what I want is my trees to haves new, healthy leaves, and so far, it was OK.

 

[Shibui]

We don't experience real cold so my knowledge is limited.
My understanding of the damage process is that the liquid inside the cells freezes and expands which ruptures the cells, in much the same way a bottle of water in the freezer will break.
The liquid inside cells is not only water. Cells contain a mix of water and salts in various concentrations. Just as sea water freezes at lower temps than pure fresh water, so cells freeze at lower temperatures. The actual temp that cell freezing takes place depends on the mix it contains. This explains why some plants are more susceptible to frost damage - some species have the ability to concentrate cell salt levels to prevent freezing.

I discussed this with an ag scientist many years ago. The gist of his research was that supplying plants with the means to increase cellular salts before frost helped mitigate damage so his advice was to supply fertilizer before freezing events to allow the plants to extract the necessary salts. He also said that if unexpected cold occurs spraying the plants with saltwater seemed to help. These measures will only increase natural frost resistance marginally but may be enough to help sometimes.

Another gardener from one of our colder areas told me that spraying plants with water BEFORE the sun came up would reduce frost damage. Not sure if this is related to the previously mentioned ability of liquid water to absorb lots of heat/cold, to place an insulated layer round the leaves or if it is just another old gardener's tale.

 

[AlainK]

spraying plants with water BEFORE the sun came up would reduce frost damage.

That's what they do in apricot orchards in the south (of France) when a slight frost is forecast. Apparently the thin layer of ice protects the buds.

 

[Potawatomi13]

Freeze damage happens even in dry air/no condensation conditions. Also effects bark of woody stems/branches if during active growth times and "hard" freeze temps.

 

[DrTolhur]

Freeze damage happens even in dry air/no condensation conditions. Also effects bark of woody stems/branches if during active growth times and "hard" freeze temps.

Do you have any further information or sources for this? If it's true, I gather the following:
1) It's due to the air temperature, not the frost itself, meaning "frost damage" is a bit of a misnomer. (Though I suppose that's not to say the frost doesn't cause its own additional damage.)
2) It's caused by crystallization of the water inside the plant.

It also might participate in explaining the "light" vs. "hard" frost concept, where the solutes in the plant water are able to lower the freezing point a little bit (say, down to around 28ºF), but not all that much.

 

[Lorax7]

Here's How to Calculate Freezing Point Depression

This example problem demonstrates how to calculate freezing point depression. Specifically, it shows how much the temperature will be lowered.

www.thoughtco.com

 

[Deep Sea Diver]

This is a good topic for a really long thread. The folks above are pretty accurate in most aspects. The mechanism is multifaceted and a bit more complicated then described above.

Here’s a diagram oriented toward that subject I recently adapted for the Azalea winter over guide I'll be posting this spring.…. ....And the latest review article... both related towards roots, yet the mechanism is similar in leaves... yet leaves aren't adapted to be as hardy so the situation is accelerated in leaves.

Also perhaps helpful is this write up on osmotic shock.

Roots are the final frontier in this area of research!

I hope this helps you.

Cheers
DSD sends

 

[Colorado]

This is a good topic for a really long thread. The folks above are pretty accurate in most aspects. The mechanism is multifaceted and a bit more complicated then described above.

Here’s a diagram oriented toward that subject I recently adapted for the Azalea winter over guide I'll be posting this spring.…. ....And the latest review article... both related towards roots, yet the mechanism is similar in leaves... yet leaves aren't adapted to be as hardy so the situation is accelerated in leaves.

Also perhaps helpful is this write up on osmotic shock.

Roots are the final frontier in this area of research!

I hope this helps you.

Cheers
DSD sends

View attachment 421979

Awesome!

 

[Potawatomi13]

Do you have any further information or sources for this? If it's true, I gather the following:
1) It's due to the air temperature, not the frost itself, meaning "frost damage" is a bit of a misnomer. (Though I suppose that's not to say the frost doesn't cause its own additional damage.)
2) It's caused by crystallization of the water inside the plant.

It also might participate in explaining the "light" vs. "hard" frost concept, where the solutes in the plant water are able to lower the freezing point a little bit (say, down to around 28ºF), but not all that much.

Personal experience ! About 7-8 years ago Eugene area had 20 degree temps one or 2 nights just as apple flowers about to open(April?). Personal nearly perfect literati Apple tree and about 6 other tree bit the dust. Bark of Apple about 3/4" diameter shrivled/wrinkled no longer smooth, brown inside dead clear down to ground! All I asked in our club lost trees that year. Hard "frost" just another term for FREEZE! If substrate freezes solid is freeze, not frost. Loved that tree.

 

[badatusernames]

If it was dipping to 30 but only for an hour overnight, would you be inclined to do the full bonsai shuffle or focus on protecting the important ones and letting the ones more in development stay out?

I figure I’ll be doing the whole shebang but I figured I’d ask first!

 

[Dav4]

If it was dipping to 30 but only for an hour overnight, would you be inclined to do the full bonsai shuffle or focus on protecting the important ones and letting the ones more in development stay out?

I figure I’ll be doing the whole shebang but I figured I’d ask first!

If 30 F for an hour, only the smallest of pots would freeze through so no big deal except if leaves have unfurled... but... weathermen get paid well to be wrong 1/3 of the time, meaning it might get colder and stay there longer. The dew point in your yard will tell you how low temps may fall... love my weather station for that. To answer your question, the newly repotted little ones and growing deciduous trees will get protected if that's the forecast. Some of my nicest trees are very cold hardy evergreens... they're heavy and I'm only going to move them if I absolutely have to!!

 

[badatusernames]

If 30 F for an hour, only the smallest of pots would freeze through so no big deal except if leaves have unfurled... but... weathermen get paid well to be wrong 1/3 of the time, meaning it might get colder and stay there longer. The dew point in your yard will tell you how low temps may fall... love my weather station for that. To answer your question, the newly repotted little ones and growing deciduous trees will get protected if that's the forecast. Some of my nicest trees are very cold hardy evergreens... they're heavy and I'm only going to move them if I absolutely have to!!

Yeah that makes sense. Outside of this single incident I was curious in general if it would pretty much insta-kill any deciduous leaves. I can get them protected.