I was reading some articles on critical spring temperatures and came across a water spray frost protection. They claimed it to be very efficient up to 22F. Unfortunately, they only say - make sure not to over-spray, as it may create ice problem. No more details on how actually do it. I could use sprayer with hot water or use hose in hand or set up sprinkler. Sprinklers I can set up on all the trees, with sprayer I can move from tree to tree, not sure how effective it could be, as I have 12 tree groups scattered over different tiers of my yard.
Temperature getting lowest for 2-3 hours (5AM-8AM), so it is kind of doable to try.
Please share your experience and thoughts.
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Galina,
This article for commercial orchards but the science behind it is the same.
It looks like you need to keep a sprinkler running until temp is above freezing/ sunrise. Too complicated for me. I would rather let the fruit buds freeze and save water.
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When ice forms it “absorbs” cold. Or “realeases” heat. Depending on how you look at it.
Cooling water down from 80 C (=176 F) to 0 C (32 F) takes roughly the same amount of “cold” as turning 0 C = 32 F water into 0 C = 32 F ice. This is what the spraying water for frost protection relies upon.
If you start with warm watter this will change verry little. (see below for how much)
This does mean however it only works as long as there is water left to freeze. And it only works in direct contact.
Basicly as long as your plants or the ice covering your plants is “wet” . Still has unfrozen water on it. It works.
If you only got a few tree’s and a slight frost. You spraying the tree’s every few minutes with a garden hose could work fine.
For a larger scale you would need overhead sprayers.
You will need to spray for as long as it’s freezing and depending on wind a little longer. So a few houres night frost will be fine.
But if it continues freezing during the day you’f got a problem. (ice cubed tree’s)
However evaporation of water takes “heat” with it. So cools down whats left. Ice can evaporate to. We call this sublimation. Ice sublimates faster when there is low reletive humidity (there usualy is during a freeze) and when there is a lot of wind.
Below ill give some examples in bold and the maths in normal text. Only read the bold if your not intrested in the rest 
Below ill write down how much heat energy it roughly takes for water to freeze or evaporate. So you can have an idea what your dealing with. Science is usualy done in SI units. So ill use Celcius or Kelvin. And “translate” that to Farenheit.
Heat capacity of water ~ 4.2 j/(g k)
(it takes 4.2 joules of energy to cool or warm 1 gram of water by 1 kelvin (1 kelvin is the same amount of temperature change as 1 celcius or 1.8 Farenheit.)
Latent heat of ice ~334 j/(g k) (also know as enthalpy of fusion)
you have to “take out” 334 joules of heat energy to change (freeze) 1 gram of water at 0 celcius to 0 celcius ice (0 celcius =32 Farenheit)
Latent heat of water vapor 2230 j/(g k) (enthalpy of vaporazation)
you have to “add” 2230 joules of heat energy to change 1 gram of water to 1 gram of water vapour
When lowering the temperature or freezing, you take heat energy "out"
The less energy you need to take “out” the easier/faster it is.
lowering water temperature by 1 C (1.8 F) is 80 times easier than freezing water.
334/4.2 = ~ 80 (devide latent heat of ice (334) by heat capacity of water (4.2)
When evaporating water heat energy is “absorbed” by the water vapor. And thus the place it evaporated from is cooled down.
Melting is what we call water going from Soldid (ice) to liquid form. Evaporation is water going from liquid to gas (water vapour) form. Sublimation is what we call water going from solid (ice) form straight to gas (water vapour) form.
Inceasing water by 1 C (1.8 F) is 530 times easier than evaporating water.
2230/4.2 = ~ 530 (devide the latent heat of water vapour (2230) by the heat capacity of water (4.2)
ill do the following examples in gallons. Since most here are from the US. But you can freely change the unit from gallons to liters or pools or oceans. The result stays the same.
Your tree’s get “heated” the same amount by
3 gallons of 86 (30c) Farenmheit water cooling down to 32F (0c) as = 1 gallon of 50 (10c) Farenheit water freezing to ice at 32F (0c)
-your blossom “feels” the same at 32F water or 32F ice. Thats why spray works so efficiantly against frost damage.
(3X30X4.2=378 joule (3 gram of water changing 30 celcius or kelvin with a heat capacity of 4.2 joules per gram per kelvin). Is roughly the same as 334+10X4.2 (334 joul per gram per kelvin is the latent heat of fusion of water. 10 is the difference in temperature and 4.2 the specific heat of water)
you would need 10% less water if your heating your spraying water from 50 F (10c) to 68F (20c)
-So spray a little more water, and don’t bother heating it.
334+10X4.2 (example above) vs 334+20*4.2 ~10% difference
It takes 6.8 gallons of 50F (10c) water freezing on your tree’s to heat them the same as 1 gallon’s worth of ice sublimating cools them down (ice going to water vapour)
-So if it’s windy and lots of sublimating is happening. You will want to keep spraying longer even after it has stopped freezing.
5X 334+10X4.2 (334+10X4.2 see example above) = ~1X (2230+334) (2230 is the latent heat of water going to vapour. +334 is the latent heat of ice going to water)
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Thanks a lot! This is very helpful!
Good luck, @galinas. I think all of us in Mass will be anxious these next two nights. Fingers crossed we come through unscathed.
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Just returned from outside setting up tarps for the plants I have frames around. Didn’t cover completely yet, just fixed sides, so it is easier to put tops in the evening. Tonight it will be raining so I am not looking forward to that task 
. It’s so weird - it is sunny, quiet and very warm outside… Can’t believe it will drop to freezing point next morning.
Wind gusts here right now. Blew over weighted closed umbrella stand. I think wrapping anything would cause more harm than good.
Woke up to three dead hermit crabs which I have had for 10 months. I feel like such a bad mama. Losing lots of fruit would definitely put me on the bad mama list. Still predicting to 32 which I think will be ok. Still pretty warm currently here too.
Best of luck @galinas
Update: I changed the water and sprayed all three hermit crabs though they appeared to be dead. When I came back they had all three crawled around!!! Maybe things arent so bad after all.
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Your point reminded me of my attempt to winter protect my fruit trees a few years ago.
I put tarps over the trees and tied them down (tightly I thought) with cords. It was a windy night. By sunrise, all those cords were twisted all over the place and broke a few branches. If I did not do anything, I would have kept those branches. Since then, I do not winter protect. Whatever happens, happens.
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Nice to hear your hermit crabs where okey.
I had a hermit crab in an aquarium (smal salt water kind) as a child. Enjoyed the heck out of those little guys watching them eat like a “old fashioned typewriter” left to right. Was really fun. Breakfast took twice as long sitting in front of the aquarium.
By your post i assume you have the larger land version though?
Did you post pictures anywhere on the forum? (is there a show your pet topic?) id love to see em 
back on topic.
If never wrapped tree’s diden’t seem worth the effort. Glad to hear that was not a mistake.
I am dreaming of building an overhead sprinkler/sprayer for frost protection for my new mini orchard though. Anyone here have experiance with such a system?
i was thinking of digging in 2-3 large IBC (900liter) water barrels. The soil heat should keep them at 5-10 ceclius (41-50F??) and installing a high pressure DC aquarium pump and using an arduino or somthing connected to a temp probe to automatrical turn it on/off.
Dunno if the head pressure from an aquarium pump would work? and what kind of sprinklers would work best? or require the least pressure?
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Conventional wisdom is overhead irrigation for frost protection takes a lot of water probably 60 Gallons per MINUTE or more per acre. I have seen some research on using micro sprinklers that use a lot less water perhaps 5 gallons per HOUR at 25 PSI so the IBC totes may work with these low flow sprinklers. Check out Netafim Supernet sprinklers - they are about $6 each. Each sprinkler will wet an area about 15 feet in diameter. We use these spinklers in our small nursery area to water containers but have never tried them for frost protection.
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They just updated our forecast. Wrong way. 
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If your temperature is the same as the forecast I wouldn’t be worried at all.
I wish… they always wrong for our location, it is usually 2-3 degrees colder…
I purposely left out some fig trees and covered with a canvas painters tarp. I was.going to use plastic but everything I read advised against it. We had six hours of freezing. Tonight down to 28. Today the wind blew them off and the leaves looked great! Tonight’s the real test! I’m optimistic it stayed below freezing forever today. It was almost 11 am before temps topped 32 I just left the fruit trees alone. Too many to protect all of them.
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I just heard a news report about an apple orchard building fires throughout the orchard. I sure hope some fruit survives in my yard. Well looking at the hardiness chart for peaches in full bloom worst case I lose 10 percent. I will remove a lot more than that I should be fine. Mine are at full bloom.
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Question about water spray protection was answered by the weather. Currently is 29 and it was the same for 3-4 hours already. And getting colder by 7 AM. To late to spray…
It was colder than expected at my place, too. Temp was down to 33 F since 2 am and stayed at 33 for a few hours and dropped to 31 F at 6 am and 7 am.
I was surprised that it was that cold that long. By that temp, fruit should be ok but the length of time that it stayed cold concerns me.
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We are at 31 here but about 2 hours Northwest of here it’s 22…yikes! Our buds should see little to no damage but this is a little to close for comfort.
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we are still 29.8