Were they covered in snow before it melted? If so they were well-protected from the cold, whether real temp or wind chill temp.

The thaw is heading this way and we are supposed to be in the 50s midweek. We have about 2' of snow that will probably all melt as well. I didn't put any protection down on the roses this year, so I hope we get replacement snow before it gets cold again!

Foghorn, the air temperature determines how cold a plant can get; the wind or the windchill determines how fast it gets there. That is, if the air temp is 0 degrees, a plant can cool to 0 degrees and no lower, but the plant will reach that 0 degree point much faster if there is a wind.

In my garden, I think windchill is of no great consequence. My roses seldom get damaged early in the winter or late in the spring. The real damage occurs in the coldest spells which occur in late January or early February here. If the winter low is 0 degrees or above, I'll see minimal damage to most of my roses. If the winter low is -5 degrees, I start to get serious cane damage and if it goes to -10 degrees, most of the canes will die back to within inches of the ground.

I think windchill is a more important factor in the milder zones. Most plants, even very tender ones, have mechanisms for dealing with mild low temperatures. These mechanisms take time, perhaps a few hours, to operate and if wind speeds up the rate of cooling, more damage can result. As near as I can figure, that's why spraying citrus crops in Florida with water, tends to decrease the damage of a cold snap. The coating of water slows the cooling rate of the plant by a few hours and the plant has time to adapt (probably by shifting water out of the cells, thereby lowering the freezing point of the cell liquid).

'Wind chill' is calculated to apply only to warm blooded animals, like people. Having lived on the edge of the Great Plains, I think there is a makable calculation regarding the effect of wind on plants, but it's completely different from wind chill. The speed and duration of the wind both have to be much greater. It's not something I've seen anywhere else I've lived. Here, give me the number at the bottom of the min/max thermometer in the spring, and I've got a very good idea how much rose damage I'm looking at.

Windchill means it feels like it is -20 or whatever, even though it is, say, 15 F.
You lose your body heat faster the greater the difference between the actual air temp & the wind chill.
That is because you are a little furnace running at a constant 98.6 F & you are always heating the air around you; wind pulls the warmth off your skin & out of your tissues faster than still air. In July we like a little windchill, we call it a cooling breeze. It's doing the same thing as it does in winter---a "nice breeze" makes us feel like it is 70 when it is 90. It pulls the heat from our skins same as it does in winter when it is not as welcome!

A rose is the same temp. as the air around it & is not producing heat, as you are from the fuel you ate for breakfast.

Foghorn likes wind chill in July!

Thanks everyone!

F.L.
NAGL

Check this out!

Here is a link that might be useful: Wind Chill Factors

Boiled down following is what it says. I've capitalized the portion that explains the effect or not on plants '

"A much overused and misused measurement
WIND CHILL FACTORS ARE SUPPOSED TO MEASURE THE EFFECT OF THE COMBINATION OF TEMPERATURE AND WIND SPEED ON HUMAN COMFORT. IT IS IMPORTANT TO REMEMBER THAT THESE DO NOT HAVE THE SAME EFFECT ON INANIMATE OBJECTS,OR EVEN ON OTHER ANIMALS OR ON PLANTS. Nor is this effect felt by humans who are sheltered from the wind.

Wind chill factors can be expressed as an equivalent temperature on either the Celsius or Fahrenheit scale, or in units of power per unit area. In Canada, wind chill factors are often reported as heat loss in watts per square metre.

Wind chill factors are often published as tables. There are many such published tables here in the U.S., and most of them don't agree exactly on all the equivalents."

It goes on to give the math that is involved figuring the wind chill factor. I didn't think you wanted that.

My first and probably only chance to correct Mike_Rivers, so I'm jumping on it.

Water is sprayed on tender plants in Florida during freezes, not just to delay the cooling, but to keep the plant tissues from cooling below 32 F. They spray continuously until the air temperature rises above 32 F. Layers of ice form on the plants but stay at 32 because new water is being added which has heat content.

Hah! Michaelg, you and I both know this is far from your only chance to correct something I wrote.

I didn't realize the water was sprayed continuously on citrus plants; I figured it was just a one shot deal in the evening. I agree then with what you wrote, and what I wrote about slowing the rate of cooling seems suspect as a major factor (I still think it's an interesting factor, though).