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#1
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Frost
Does the temperature have to be at or below freezing for frost to form on
plants? Thanks |
#2
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Frost
In article ,
"Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks http://en.wikipedia.org/wiki/Frost Notice the mention of dew point. Bill who thinks the frost acts like a magnifying glass hence the plants burn. Not sure if this is correct only know that late frost about here has me out spraying water on tender new plants. -- Garden in shade zone 5 S Jersey USA We have 5% of the world's population; we have 25% of the world's known prison population. |
#3
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Frost
On 3/28/2009 12:53 PM, Bill wrote:
In article , "Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks http://en.wikipedia.org/wiki/Frost Notice the mention of dew point. Bill who thinks the frost acts like a magnifying glass hence the plants burn. Not sure if this is correct only know that late frost about here has me out spraying water on tender new plants. Liquid water from a hose is above freezing. In the process of turning into ice, such water must first give up heat just to be chilled to 32F (0C); then it must give up significantly more heat just to become ice even if the temperature remains at 32F. That's why farmers in my area spray water on citrus, avocados, strawberries, etc if there is a late freeze. For "radiation frost" with air temperatures above freezing (described in the Wikipedia article you cite), they do nothing since those crops are generally hardy enough to withstand the chill. -- David E. Ross Climate: California Mediterranean Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean influence (USDA 10a, very close to Sunset Zone 19) Gardening diary at http://www.rossde.com/garden/diary |
#4
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Frost
On Sat, 28 Mar 2009 15:33:28 -0500, "Denis Mitchel"
wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks For moisture or water to freeze the temperature must be no higher than 32 degrees F, and then additional heat must be removed for the water to phase-change to a crystal lattice structure (ice). No ice will form above 32 degrees, but certainly there can be supercooled (or contaminated) liquid water below 32 degrees, which is added frost protection for the plant. |
#5
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Frost
In article ,
"Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks Below freezing, because the plant(s) will carry over some heat from the day and the ground, if dry, will be reflecting some heat as well. This heat must be removed before freezing can occur. As Bill alluded to, as long as your making ice (there is water to freeze) the ice will remain at 32F (0C). -- - Billy "For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death." - Rachel Carson http://www.youtube.com/watch?v=WI29wVQN8Go http://www.haaretz.com/hasen/spages/1072040.html |
#6
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Frost
"Denis Mitchel" wrote:
Does the temperature have to be at or below freezing for frost to form on plants? No. The dew on plants can freeze without the air temperature dropping to below 32ºF... this often occurs with lawns and other low growing plants because even though the air near the ground is heated by the radiant heat to above 32ºF yet the fine droplets will freeze... fog can freeze and settle on plants (like snow). But just because the dew freezes on the plant doesn't mean the plant freezes, many plants contain chemicals that act as antifreeze, and many plants will suffer 'frost' damage above freezing, especially young tender seedlings. There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. Why do you ask? |
#7
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Frost
In article ,
"brooklyn1" wrote: "Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? No. The dew on plants can freeze without the air temperature dropping to below 32ºF... this often occurs with lawns and other low growing plants because even though the air near the ground is heated by the radiant heat to above 32ºF yet the fine droplets will freeze... Because . . . . ? fog can freeze and settle on plants (like snow). Fascinating, can we have a cite? But just because the dew freezes on the plant doesn't mean the plant freezes, Uh huh, I think we already covered the heat of fusion. many plants contain chemicals that act as antifreeze, and many plants will suffer 'frost' damage above freezing, especially young tender seedlings. There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. And that reason is . . . ? Whatever the true identity of brooklyn1, brooklyn1 certainly is as scatter brained as Shelly, who has a thing for forest pansies, heh, heh (as Shelly would say). Still, one last wrinkle. Wind chill could allow standing water, as small as a dew drop even, by evaporative cooling in conjunction with low temperatures. -- - Billy "For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death." - Rachel Carson http://www.youtube.com/watch?v=WI29wVQN8Go http://www.haaretz.com/hasen/spages/1072040.html |
#8
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Frost
brooklyn1 wrote:
"Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? No. The dew on plants can freeze without the air temperature dropping to below 32ºF... this often occurs with lawns and other low growing plants because even though the air near the ground is heated by the radiant heat to above 32ºF yet the fine droplets will freeze... fog can freeze and settle on plants (like snow). I think you have this backwards, the air near the ground is cooled by radiant loss of heat in frosty conditions. Under a clear sky frost can form at or near the ground even though the "official" temperature is not below freezing. This is because the recorded temperature is taken above ground (I forget the distance but it's about 4-5ft) while the temperature on the ground can be quite a few degrees lower due to radiant heat loss. But just because the dew freezes on the plant doesn't mean the plant freezes, many plants contain chemicals that act as antifreeze, a True and many plants will suffer 'frost' damage above freezing, especially young tender seedlings. yes There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. Dew point is another way of saying humidity, it is the temperature at which, with the current moisture content, the air would reach saturation. If the dew point is near the "official" air temperature (above the ground) then on the ground the temperature may below precipitation point. I cannot see why you relate it to barometric pressure or elevation David |
#9
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Frost
In article ,
"David Hare-Scott" wrote: brooklyn1 wrote: "Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? No. The dew on plants can freeze without the air temperature dropping to below 32ºF... this often occurs with lawns and other low growing plants because even though the air near the ground is heated by the radiant heat to above 32ºF yet the fine droplets will freeze... fog can freeze and settle on plants (like snow). I think you have this backwards, the air near the ground is cooled by radiant loss of heat in frosty conditions. Under a clear sky frost can form at or near the ground even though the "official" temperature is not below freezing. This is because the recorded temperature is taken above ground (I forget the distance but it's about 4-5ft) while the temperature on the ground can be quite a few degrees lower due to radiant heat loss. Evaporative cooling could suck a lot of heat out of wet ground, not so much with dry soil. But just because the dew freezes on the plant doesn't mean the plant freezes, many plants contain chemicals that act as antifreeze, a True and many plants will suffer 'frost' damage above freezing, especially young tender seedlings. yes There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. Dew point is another way of saying humidity, it is the temperature at which, with the current moisture content, the air would reach saturation. If the dew point is near the "official" air temperature (above the ground) then on the ground the temperature may below precipitation point. I cannot see why you relate it to barometric pressure or elevation David Barometric pressure (air pressure) changes with elevation. In the heart of Jupiter (a gas giant), H2 is a solid because of the immense pressure of its' atmosphere. Contrarily, water will boil at room temperature in a vacuum. Some where between these two extremes, air pressure will have some effect on the formation of dew or the deposition of frost (phase changes), as will the humidity of the air. -- - Billy "For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death." - Rachel Carson http://www.youtube.com/watch?v=WI29wVQN8Go http://www.haaretz.com/hasen/spages/1072040.html |
#10
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Frost
"Billy" wrote in message ... In article , "David Hare-Scott" wrote: brooklyn1 wrote: "Denis Mitchel" wrote: Does the temperature have to be at or below freezing for frost to form on plants? No. The dew on plants can freeze without the air temperature dropping to below 32ºF... this often occurs with lawns and other low growing plants because even though the air near the ground is heated by the radiant heat to above 32ºF yet the fine droplets will freeze... fog can freeze and settle on plants (like snow). I think you have this backwards, the air near the ground is cooled by radiant loss of heat in frosty conditions. Under a clear sky frost can form at or near the ground even though the "official" temperature is not below freezing. This is because the recorded temperature is taken above ground (I forget the distance but it's about 4-5ft) while the temperature on the ground can be quite a few degrees lower due to radiant heat loss. Evaporative cooling could suck a lot of heat out of wet ground, not so much with dry soil. But just because the dew freezes on the plant doesn't mean the plant freezes, many plants contain chemicals that act as antifreeze, a True and many plants will suffer 'frost' damage above freezing, especially young tender seedlings. yes There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. Dew point is another way of saying humidity, it is the temperature at which, with the current moisture content, the air would reach saturation. If the dew point is near the "official" air temperature (above the ground) then on the ground the temperature may below precipitation point. I cannot see why you relate it to barometric pressure or elevation David Barometric pressure (air pressure) changes with elevation. In the heart of Jupiter (a gas giant), H2 is a solid because of the immense pressure of its' atmosphere. Contrarily, water will boil at room temperature in a vacuum. Some where between these two extremes, air pressure will have some effect on the formation of dew or the deposition of frost (phase changes), as will the humidity of the air. Exactly. Often the frost one sees on lawns during early morning is actually precipitation... the water in the ground evaporates, rises to a colder air layer (albiet a low altitude, perhaps just a few feet), where those small droplets freeze and fall... what one sees on plants that's called frost is actually a fine snow. As soon as the sun appears the frozen droplets will melt and evaporate, if it stays cloudy the radiant heat from the ground will eventually melt the frozen droplets, they will condence into larger droplets, rain down and be reabsorbed into the ground. The frost one sees on plants protects them through insulation, it acts as a buffering layer (same as layered clothing, same way igloos insulate, ice contains a lot of traped air, air is an excellent insulator) just in case more fridgid air comes barreling in. The occurance of frost is very random (can't be predicted with any degree of accuracy) and is dependant on a delicate balance between many meteorological factors. Don't confuse frost with a soft and hard freeze. I've often seen heavy snow squalls pass through here in late April early May when temperatures are above 60ºF... could be like a half inch accumulation. It quickly melts as the dark clouds scud past, caused no plant damage unless accompanied by high winds... nature's way of pruning weak wood. |
#11
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Frost
Billy wrote:
There's good reason why weather forcasters mention "dew point", has to do with barametric pressure/elevation. Dew point is another way of saying humidity, it is the temperature at which, with the current moisture content, the air would reach saturation. If the dew point is near the "official" air temperature (above the ground) then on the ground the temperature may below precipitation point. I cannot see why you relate it to barometric pressure or elevation David Barometric pressure (air pressure) changes with elevation. In the heart of Jupiter (a gas giant), H2 is a solid because of the immense pressure of its' atmosphere. Contrarily, water will boil at room temperature in a vacuum. Yes Some where between these two extremes, air pressure will have some effect on the formation of dew or the deposition of frost (phase changes) Maybe, but how much? I am not saying you are wrong but what effect will it have and is it worth worrying about? In what situation would this effect make a practical difference? , as will the humidity of the air. I think we all agree on that. David |
#12
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Frost
On 3/28/2009 12:33 PM, Denis Mitchel wrote:
Does the temperature have to be at or below freezing for frost to form on plants? Thanks We often get frost on roofs when the overnight air temperature stays above 32F. I think this is a case of the roofing materials radiating enough heat into a clear, cloudless sky that they might actually be colder than the air. For plants, however, I don't think they can lose enough heat to drop their temperatures below that of the surrounding air. Thus, frost might form on plants until the air temperature is actually at or below freezing (32F, 0C). -- David E. Ross Climate: California Mediterranean Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean influence (USDA 10a, very close to Sunset Zone 19) Gardening diary at http://www.rossde.com/garden/diary |
#13
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Frost
In article ,
"David E. Ross" wrote: On 3/28/2009 12:33 PM, Denis Mitchel wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks We often get frost on roofs when the overnight air temperature stays above 32F. I think this is a case of the roofing materials radiating enough heat into a clear, cloudless sky that they might actually be colder than the air. For plants, however, I don't think they can lose enough heat to drop their temperatures below that of the surrounding air. Thus, frost might form on plants until the air temperature is actually at or below freezing (32F, 0C). Huh? -- - Billy "For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death." - Rachel Carson http://www.youtube.com/watch?v=WI29wVQN8Go http://www.haaretz.com/hasen/spages/1072040.html |
#14
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Frost
On 3/28/2009 6:37 PM, Billy wrote:
In article , "David E. Ross" wrote: On 3/28/2009 12:33 PM, Denis Mitchel wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks We often get frost on roofs when the overnight air temperature stays above 32F. I think this is a case of the roofing materials radiating enough heat into a clear, cloudless sky that they might actually be colder than the air. For plants, however, I don't think they can lose enough heat to drop their temperatures below that of the surrounding air. Thus, frost might form on plants until the air temperature is actually at or below freezing (32F, 0C). Huh? Live foliage does not radiate heat into a cloudless sky as readily as do metals and minerals. By the way, because of dissolved substances (e.g., sugars) in the moisture that is internal to plant tissues, that moisture has a lower freezing point than 32F. -- David E. Ross http://www.rossde.com/. Don't ask "Why is there road rage?" Instead, ask "Why NOT Road Rage?" or "Why Is There No Such Thing as Fast Enough?" http://www.rossde.com/roadrage.html |
#15
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Frost
In article ,
"David E. Ross" wrote: On 3/28/2009 6:37 PM, Billy wrote: In article , "David E. Ross" wrote: On 3/28/2009 12:33 PM, Denis Mitchel wrote: Does the temperature have to be at or below freezing for frost to form on plants? Thanks We often get frost on roofs when the overnight air temperature stays above 32F. I think this is a case of the roofing materials radiating enough heat into a clear, cloudless sky that they might actually be colder than the air. For plants, however, I don't think they can lose enough heat to drop their temperatures below that of the surrounding air. Thus, frost might form on plants until the air temperature is actually at or below freezing (32F, 0C). Huh? Live foliage does not radiate heat into a cloudless sky as readily as do metals and minerals. By the way, because of dissolved substances (e.g., sugars) in the moisture that is internal to plant tissues, that moisture has a lower freezing point than 32F. The confusing bit is, "Thus, frost might form on plants until (32F, 0C)." It seems to imply that once "the air temperature is actually at or below freezing", frost formation will stop. I doubt that is what you were trying to say but that is what you said. -- - Billy "For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death." - Rachel Carson http://www.youtube.com/watch?v=WI29wVQN8Go http://www.haaretz.com/hasen/spages/1072040.html |
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