Frost question

[Paul Ont]

Does anyone know whether frost occurs every time the dew point is below freezing? I notice that a lot of people post that they've not had frost but have had temps at, or close to, 0C...

Does a dry climate have frost a lower temperature than a 'wet' one?

[TerdalFarm]

Paul,
thanks for asking. I admit to being confused about frost as well.
My guess is that Barb will have a helpful link for us....
I had my first front last week, but the air temp was 33 oF / 1 oC yet it was a real frost--just ask my Musa (except M. basjoo) or Ipomoea (sweet potato). Or Colocassia. Or the pasture grass. I saw frost on the leaves, so I know they got hit despite my air. temps barely above freezing, let alone very warm soil temps.
--Erik

[hardyjim]

Does anyone know whether frost occurs every time the dew point is below freezing? I notice that a lot of people post that they've not had frost but have had temps at, or close to, 0C...

Does a dry climate have frost a lower temperature than a 'wet' one?

Not necessarily but.............

A very dry atmosphere can keep you from having frost as well as any air movement,
plant tissue is very susceptible though as it does give off water,that's why development is most favorable on calm nights..

[Paul Ont]

Thanks for the replies guys! Hoping Barb will have an interesting link on the subject!

[Cowtown Palm Society]

Hi Paul,

Does anyone know whether frost occurs every time the dew point is below freezing?

Third edit: I believe it occurs every time the air temperature (or more importantly, in this case, the ground or plant temperature) meets the dew point (frost point in air temps. below 0c). If this is what you mean, then yes. If you mean however: will there be frost (assuming suitable conditions ie clear skies, no wind etc.), for example, with an air temp of -1c and a frost point (dew point) of -5c?- then the answer is-I think (God, I'm a nerd) sometimes, albeit rarely, no.

Take very dry Las Vegas, NV, for example. You'll see ridiculously low relative humidity there-sometimes below 10%. I'm sure I've seen dew points there of like -7C (in which case it actually becomes the "frost point temperature"). In this case, wouldn't there be an absence of frost (due to lack of humidity) at temperatures from -6C and warmer, even when air temps. are below freezing? I think typically, such low dew/frost points only occur when high daytime temps. blaze away any humidity, hence no chance of a freezing night. But I don't think it's all that rare for Vegas to see calm, clear and frostless nights down to even -1 or -2C because there is so little humidity in the air. This is, of course, not to say, that a freeze has not occurred-just that frost has not.

Disclaimer: Paul and everybody, I could very well be way out to lunch on this, but like most people who fill cyberspace, I feel, nonetheless, compelled to offer my two cents. I would love to know that I'm wrong about this!

Thanks!

Cliff Claven Wanna Be

[TerdalFarm]

Paul,
these photos could have gone under your fried bananas thread but I think they fit here, too.
As I said above, I did not get a real freeze here last week. The last week of October is our customary first freeze, but I'm up on a hill and cold air sinks. I thought I lucked out again as my air temp. only got to 33 oF / 05 oC but I did see a frost on plants despite the air (+ soil temps at 10 cm of 20 oC).
The plants felt it. This photo from this evening is proof. We have had very warm temperatures since the brief frost (e.g., 80 oF / 27 oC afternoons). However this Musa suffered. The second photo from several steps back shows that the garden in general looks OK.

<table style="width:auto;"><tr><td><a href="http://picasaweb.google.com/lh/photo/y2 ... site"><img src="http://lh4.ggpht.com/_r-MvN4jW1sE/TM9oO ... AG0317.jpg" height="800" width="478" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="http://picasaweb.google.com/terdalfarm/ ... ">November 2010</a></td></tr></table>



<table style="width:auto;"><tr><td><a href="http://picasaweb.google.com/lh/photo/RQ ... site"><img src="http://lh3.ggpht.com/_r-MvN4jW1sE/TM9oZ ... AG0318.jpg" height="478" width="800" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="http://picasaweb.google.com/terdalfarm/ ... ">November 2010</a></td></tr></table>

[Paul Ont]

FYI my garden got nailed again last night. Growing season is definitely over now. 2 nights in a row of temps at or below -4C (25f) have made sure of that! Interestingly, the lows at the closest weather station (Kingston airport) were 1C the first night, and -4C (i.e. the same) last night. I have no idea why.

Only a 3 hour drive away here in Toronto there are still Cannas blooming... Though, as I said before we have had frost and have been within a degree Celsius of a freeze.

[igor.glukhovtsev]

I remeber you gyus were suprised when I were informed you about the first snowfall happens a couple weeks ago. Look at the picture:

Today I checked my Fuchia magellanica it's still blooming and there is no sign of a light frost happened...

[hardyjim]

WOW' that's a lot of snow!

One example of how much damage frost verses freeze can issue is this....
my Castor bean plants out in the open and exposed are fried,end of story for them.
The Castor bean plants under a Maple(that still had leaves on it at the time)are fine,
almost no visible damage at all,all this after temps surely cold enough to eliminate them.

Also,the Tetrapanex under the Maple is lovely,the other more exposed melted down,
same goes for my Basjoo,the one on the east (protected)side of the house is fine.

Approx 26-28f in the front yard,frost on leaves certainly is quite the catalyst!

[igor.glukhovtsev]

Jim, I had a chance driving 25 km all the way from my place (1000 m above sea level) down to the airport area (700 m above sea level) today. Roses are ok (blooming like crasy) as well as the Castor bean plants. Awaiting for the next season with my Wagner, Chamerops, Basijoo, Gunnera and other stuff I bought recently.

[hardyjim]

Post some pics,I would love to see them.

Waggies are one of the best cold hardy palms period,none of mine have ever had complete spear-pull

[lucky1]

Great Question Paul.
I think we've all puzzled over that now and then.

...just happen to have this:
http://www.suite101.com/content/underst ... ion-a42645

Even though Vancouver has recently been pounded with rain we've been dry dry dry, no dew in the morning.
But it's also been really warm 18C this p.m.
We're expecting 0C tonight but with the dry air, doubt we'll see anything looking white tomorrow at dawn.

Barb

Edit: Agree with Cliff Claven 100%