Around here when it gets cold- it's cold. But the point of wrapping plants isn't thermal protection really. Heaven knows burlap don't got much thermal value. It's more for other weather concerns that go along with those really cold temps. It helps with moisture retention in the plant and preventing wind stripping- which can also help temper frost cracking. It prevents ice and snow damage, and helps decrease storm damage. In some cases if it's a plant that can lose foliage or become winter open, wrapping can help prevent sun damage. Not temps, but wrapping helps protect against critters too. Sometimes it's because the plants are close enough to the road that wrapping helps keep the plow road gack off them.

Around here some folks do thermal protection too. That more often looks like bagged leaves or a leaf cage or straw bales around a smaller plant. The occasional run of a pair of snow fences to corrall a row of plantings under leaves. And a bunch of styrofoam rose covers. For sure a different thing than wrapping.

Now, if it's just frost protection and not extended real cold... that can often be well helped with a frost blanket. I've used frost cloths as season extenders or for quick protection in case of an unexpected late frost/cold snap in the spring. Works great. But also not wrapping.

Well, all those other weather concerns are also appropriate for temperatures above freezing. But around here, people wrap their plants if the temp is going to drop below 32F. That's why they're doing it. To protect from a freeze. It doesn't.

Is there a link to the paper you published on your research? In it's totality ,what you've said here doesn't explain why different folks see different results. More importantly I'd like to know why I see different results from identical plants within 3 feet of one another. This year as in years passed I extended production (on vine ripening) of 3 tomatoe plants by covering them first couple times temperatures dropped. Plants which I did not cover suffered damage. There have been times when I lost plants I neglected to cover while my neighbors plants he covered did well, and vs vs. Has your research revealed anything that might account for those discrepancies?

I do thermal engineering for a living. You want to argue? If you covered something and included soil under your cover, you'd done it right. If you just wrapped the plants, they would not have survived. Just that simple. That's experience, and physics. Plants don't generate heat, so when you wrap them, there is nothing to keep them warm. If you wrapped a brick in plastic, you think the brick would be warm? Yes, it would stay warm longer than if you didn't wrap it, but not that much longer. The soil is a huge heat sink, and will radiate heat into any cover over it.

Sounds like teaching pigs to whistle but if it makes you feel good go for it.

I'm just making a point that might save folks some trouble. Lots of people around here are going to lose plants because they protected them wrong. They might not feel that good afterward.

" Plants don't generate heat "

And I'd argue that they do. Not all plants and not consistently but you might learn something by investigating thermogenic plants.

I'd better tell my neighbors that they can save their Eastern Skunk Cabbage spadix by wrapping it, if they can get past the smell.

Heh, you might want to tell your neighbors about what you see them doing with wrapping since they are the ones you see issues with. I'm not too sure how many people around here are having issues with their wrapping practices.

I've told them, but they just shrug and say, eh, but I can't do anything else! To the extent people around here have issues with wrapping for frost protection, be advised. But when wrapped frost intolerant stuff dies in a freeze, people mostly just say, oh, it was just too cold. No issue. Seriously, wrap a thermometer in a layer of plastic or put it in a bottle and set it outside in a freeze. See what it reads. Surprise!

Here your opportunity to use your science skills and help everyone everywhere. Engineer a thermal tent with a layer of added soil, because "the soil contributes heat". If you can make it work, you can patent it for profit.

Thermal tent? Just make a tent over soil. Native Americans could do it. You can too. Then again, you can pretend it's an engineering problem.

I told the woman I've been "staying with" past 60 years I was going to skip vacuuming our floors and allow soil to contribute free heat. She didn't mince words telling me what she thought about the excus,,,,,,,plan.

Well, true, you wouldn't want to go outside and vacuum up the soil!

The last time I used plastic sheeting to protect plants from freezing it worked, but I had to install a couple of light bulbs to make it work. My extra early corn experiment from a few years ago...

I remember that pic vgkg. But I can't remember how that turned out for you. What eneded up happening there?

I've not gotten to the point of adding in lighting heat that. I've thought about it on a couple of the caps over the kitchen containers. I'm almost at year round growing in them, but not quite. I still lose to the deep cold like now when it's been in the lower 20's for a while. But in just a few short weeks I can start putting super cold hardies out there.

The 2nd law of thermodynamics validates your assessment and eventually the ambient temperature inside the wrapped plant will reach equilibrium with the outside temperature and freeze the plant. But you mentioned frost protection, and slowing the transfer of energy for a short period of time is usually the purpose of covering plants for FROST PROTECTION and common practice. Clarification of what conditions you're referring to is needed.

Trying to protect plants from a frost compared to a hard long freeze are entirely different situations and success depends on time and temperature for both. Are the plants actively growing? Are the people you see doing this just trying to rise the cold hardy zone by a factor of one for dormant plants? Wind speed accelerates the transfer of heat lowering the time variable and can easily been seen if you've spent time in blast freezers like I have.

Just for argument's sake ALL plants will release a slight amount of heat when actively growing when sugars are used by the plant cells, and the 2nd law of thermodynamics also covers this. The transfer of energy from one form to another used as work is never 100% efficient in any process, and some energy will be lost in the form of heat but is negligible and not a factor in this discussion.

Wrapping a plant in one layer of plastic doesn't slow the cooling much. If you wrapped the plant in a thick layer of insulating material, maybe thick foam or home insulation batting, that might slow it a bit. But no one does that.

I'll say it again. Wrap a thermometer in a sheet of something or other and set it out in a freeze. Within a few minutes, it will be at the air temperature.

Oh dear, arguing about facts and basic physics. I offered this as friendly advice. Yes, one could argue that when you drop a trowel it really flies up into the air, that wood doesn't really burn in a fire, or that plants don't really get wet when it rains. But things are kinda slow here these days, so ...

Ok Dan, I placed a digital thermometer in a gallon plastic bag full of 55 degree air outside where the temperature is 18 degrees and guess what? After an hour the temperature inside the bag is at 28 degrees and didn't take minutes. And as the temperature in the bag drops the time it takes to drop becomes even longer. It will take many hours before the temperature reaches 18 degrees, and going from 19 to 18 may take a couple of hours.

There is this silly little rule about heat transfer, as the temperature difference between two spaces (delta) drops the rate of transfer also slows, and as the two differences come closer the transfer rate slows to a crawl. Kind of thought you'd know this working in Thermal engineering,

So if a human covers a plant with thin plastic the night before a temperature drop down to 30 the chances of the plant being subjected to 32 degrees during the night and early morning is very slim, and depends on the time the temp stays below 32. Not minutes but many hours before the temperatures reach equilibrium.

Update; Another 30 minutes later and the temperature in the bag is 26 degrees. 60 minutes to drop 28 degrees and than 30 minutes more to drop another 2 degrees, it will take many hours to get down to 18.

2nd update: in the last hour and 45 minutes outside temperatures rose to 21 degrees, and the bag is 26.5 degrees so the delta is 5.5 degrees.

3rd update: Outside temperature rose to 22 degrees but whats odd is the bag temperature climbed up to nearly 27.5. It's not in the sun or wind so maybe a error someplace on my part. Started at 11:23 and now 2:05 so about 2 hours 40 minutes into it. Not minutes but HOURS and a long long way to go.

Fair point, but freezing weather lasts for days. If I'm trying to protect for a freeze that lasts a few hours, wrapping might do the trick. But that's never the case. You should understand that. Also, as noted, sunlight on the bag will heat up the inside. But that won't happen at night, and night is when it gets especially cold.

I am getting the impression that gardening life is kind of boring these days for many, and people just want to argue. My southern crops are going strong, however, so I'm just going to drop it and get back to work outside. If anyone wants to assert a credible argument for wrapping plants to protect them from a freeze, have at it. Haven't heard any yet.

Beesneeds, It worked 75/25. The corn grew well and survived the lower 20'sF during that cold March. Unfortunately, planting that early (March) I had run out of my favorite corn seed from the previous season (Ambrosia) so had to settle for what was off the local seed rack here at the time (Candy corn). It was a so-so corn but it did grow ok with the help of the plastic covering over a hooped enclosure with 3 - 75W incandescent light bulbs to prevent freezing. I also installed a remote thermometer inside under the plastic and kept tabs on the temp. On warmer days I would peel back the plastic to prevent popcorn ;-). I haven't tried it again since back then, I must have been pretty bored during that March, nyuk.

Final results from putting a thermometer in a plastic bag outside. After 7 full hours with outside temperatures starting at 18 and going to 22 and back to 20 the digital thermometer inside the bag was at 23.5 degrees. 7 hours and never dropped to the outside ambient temperature.

A thin plastic covering over plants will protect them from frost damage for many hours, and if the temperature held at 20 degrees I'd estimate the bag temperature would still be higher after many more hours.

"but freezing weather lasts for days. If I'm trying to protect for a freeze that lasts a few hours, wrapping might do the trick. But that's never the case."

Actually, it is the case in the North. Gardeners do not grow sensitive plants outside in the Winter, so the protection is for cold nights in Spring and for extending the growing season in Autumn, so it IS meant to protect for a few hours until it warms up with sunlight.

Could you give an example of what plants you are referring to/ complaining about? What would you do instead to be helpful?

I have to admit I'm a bit curious too as to what the neighbors are growing and how they are wrapping them to cause the OP to start a rant thread berating Houzz gardeners about it.

Vgkg, thanks for the reminder on the corn. I think a lot of winter gardeners end up doing some projects that in hind sight... heh. I have an old three chamber dog kennel that I wrapped in plastic as a "instant" greenhouse. It worked great, but man, in hindsight, heh. Once it started going to mess it was indeed a mess.

The reason we wrap plants over winter up here is for wind protection, not cold protection.

It's not a fallacy. While you are correct about soil exposure and the tent effect, you're ignoring one major aspect: radiative transfer.

The whole sky above is, let's say, a heat vacuum. When it's the warm season, water vapor acts as a great heat reservoir and insulates us from the mostly thermally void space. When the atmosphere is dry, that insulation is reduced--which just so happens coincide with cold fronts and the subsequent freezing situations (remember that the atmosphere can hold water vapor exponentially more, or less, in respect to temperature).

If clouds are present, they are a radiative barrier/buffer from space. Instead of being the unblocked atmosphere's thermally 250K, the clouds might be around 273K. They'll radiate out their thermal mass, warming the ground beneath them, and also providing an environment where the ground isn't exposed to 250K; rather, 273K. The ground is much warmer as well.

When plants are covered, those materials provide a buffer from that 250K open atmosphere. The plant might instead encounter 270K, which hopefully is enough to survive the freeze. Note that contact with the covering material will likely freeze the exposed plant material.

This is, of course, ignoring wind impacts. Wind and associated thermal conduction will overpower any radiative impacts handily.

tldr; covering with exposed ground or soil in the same tent is the best practice. Covering partially is less beneficial, but not useless.

Air temperature is VASTLY more important in thermal equilibrium than exposure to cold sky. If the air temperature is below freezing, wrapping a plant won't make it any warmer than the air temperature. Think you're going to melt an ice cube by wrapping it up? Or, go ahead and wrap a thermometer, and see if it is warmer than an unwrapped thermometer.

We can both agree that tenting a plant with soil is the far superior approach. Air temperature is vastly more important when it's windy and the atmosphere is mixing, yes.

What about calm nights, though? Remember that foliage has a thermal emissivity of nearly 1, meaning it's very good at radiating away energy. I'm sure you've seen frost form on grass when the air temperature is above freezing (like 36*F) on calm, clear nights. That means that objects can actually get quite a bit colder than air temperature in that scenario. By that same logic, covering plants (without soil) will mean that the cover will be radiating energy to space and become colder than air temperature, sparing the plant that fate. Is it great? No, but it's better than nothing. That 1*F delta may mean the difference between death and survival.

This principle is how atmospheric inversions form on calm nights.