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jal_ut
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Re: I'm Confused (Frost Damage)

Dew point:

Air can hold water vapor , this is measured as humidity. Warm air can hold more water than cool air. As air cools, a point is reached where the air cannot hold any more water, and if it cools more, some of the water condenses out of the air and becomes liquid water. This is the dew point. The liquid water that collects on cool objects in the area is dew. The dew point (temperature) can be different depending on what the relative humidity of the air was. This has nothing to do with frost nor freezing.

Freezing:
By definition this is the temperature where liquid water turns to solid water, that is ICE. Frost = ice.
It is 32 degrees F where this happens. You cannot have frost unless the temperature gets that cold. Absolutely impossible.

So your plants got blackened? It sounds like they got frozen. To freeze the temperature at the level of the plants had to be 32° F or lower. That is just a simple law of physics.

Sorry you got hit. The potatoes will recover. I am surprised the peas took a hit. They usually have pretty good resistance.

A cover like a blanket is better than a bucket or jar as it has better insulating qualities.
It is good to wet things down well if expecting a frost. Water is interesting in that it must give off quite a little heat even after reaching 32° before it will change state (freeze). So more water = more heat.

It soon becomes obvious that there are cold pockets and six thermometers in six locations will all read different. Best to expect frost any time the forecast is for under 40°.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-

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applestar
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Re: I'm Confused (Frost Damage)

I see, so, and I think we are all talking about the same thing in the end -- but at ground level in "cold pockets" the temperature fell to -- or below -- freezing (32°F) where frost formed.

...and perhaps in the OP's garden, the temperature perhaps fell significantly and for a prolonged period? Damage seems too severe to be light or even simple frost -- more consonant with hard frost or freeze.

Thank you for elaborating the dew point definition. I think I get it now, especially after re-reading the different posts referencing dew point. :D

Here's an interesting correlation I've often noticed: the forecast temp is often wrong (too high by 2-3 degrees), but the dew point in the forecast is often the temperature I get on my porch thermometer.
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.

SOB
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Re: I'm Confused (Frost Damage)

For the record the recorded low temp for my area was 35 degrees. I understand that my garden could have experienced temps lower than this. Also, FWIW, the dew point was 32. I do know that we experience a recorded temp of 33 degrees the following day and there were no frost warnings because it was cloudy and breezy. It's my understanding that the cloudy breezy nights don't allow the moisture to settle on the plants. I did cover that night too just to be sure.

Is there a possibility I covered the plants too early and the sun warmed inside the buckets causing condensation which then froze causing extra damage?

The main point I took from the conversation above was that buckets are not the best covers. What I don't get is I see people covering things with thin sheets that have very little insulating properties and they seem to have no problems. I guess next time I'll break out some old sheets.

I looked again last night and the potatoes look like they will make it. They definately lost a out 75% of their foliage though. Peas look fine now. The broc/caul/cabb weren't a total loss but pretty close. I'm not too worried about that as I will probably grow a fall crop. What I will do in the future is start those crops indoors so they can get bigger and then be hardened off. Maybe that will give them a better chance.

Thanks all!

cynthia_h
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Re: I'm Confused (Frost Damage)

Freezes aren't that common in the part of the Bay Area where I live, so the garden advice is always repeated: "Do not cover your plants with plastic sheeting because any part of the plant that touches the plastic can freeze." Then they go on to recommend cloth, or plastic sheeting up on sticks away from the plants, etc.

Even in one's own yard, whether a large property, a "standard" suburban quarter-acre lot, the 50'x100' lot DH and I have now, or the 25'x80' (I think 80', might have been 100' from the street) lot we had in Berkeley, there are microclimates (sometimes referred to as micro-zones) where the temps can vary by as much as 5 degrees F (approx. 3 deg C). In December 1990 or 1991, whenever The Big Freeze that destroyed the California citrus crop hit, DH and I kept our cymbidiums and a few other plants alive on the patio in Berkeley in 28 deg F weather for several days, including one night at 25 or 26 deg, by:

1) clustering all the cymbidium pots under the avocado tree,
2) watering them with warm water right before going to bed (the planting medium only, not the leaves or plants proper),
3) propping old sheets over the orchids and other container plants using sticks so we could get "just a couple more" plants :wink: under shelter, and
4) running a heavy-duty extension cord and attached household heater (meant for use under a desk or table) under the sheet covering the plants while we were asleep. We later added a string of twinkling Xmas lights so that more plants would have something in the way of warmth.

It was quite a bed-time ritual for that week or so: first, lugging warm water out to the plants in watering cans over multiple trips (that house had only a shower, not a tub, so the kitchen was called into service; the kitchen was farther from the back door than the bathroom was--of course); second, setting up the sticks-and-sheet "superstructure," once we'd figured out just how many of our plants we could fit under it, and third, turning the heater on and plugging the lights in.

We saved all but one of the plants, and all of the cymbidiums. :) Nothing in the front yard died, though, so I think the front yard must have been 30 or 31 degrees with very little humidity. Certainly not nearly as cold as the back yard, a postage-stamp sized thing surrounded by fence, house, etc. with almost no air circulation.

Maybe some of these tips will help when the temps are threatening again.

And, believe it or not, I had to do Snail Patrol each of those freezing nights! The little beggars were trying to sneak onto the patio for the heat, no doubt, or to eat the other plants. Just made them more visible to me.... :twisted:

Cynthia H.
Sunset Zone 17, USDA Zone 9

SOB
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Re: I'm Confused (Frost Damage)

UPDATE: I replanted most of the tomatoes that got killed in the frost. Everything else snapped back. I have a total of 10 tomatoes and since then I planted my 6 bell peppers, 2 hot peppers, 2 eggplant and various herbs. Also, some of my beans and cucumbers came up.

Then...Friday night I knew it was going to get on the cold side (they were calling for 38) but there were no frost/freeze warning so I figured I was OK. Boy was I wrong! I walked out to the garden Saturday morning and EVERYTHING I had just planted was dead! I felt like puking.

I spoke with my neighbor (her garden is probably a good 1000 feet from mine, roughly the same elevation and just as open meaning no trees or structures) and she had ZERO damage to her veggies?! She didn't cover them or anything.

Sunday I bought a couple tomatoes so we have SOMETHING this year and I still had one eggplant left over that survived under the patio. I'm not buying anything else! I guess next year I have to wait until Memorial Day to plant!

JayPoc
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Re: I'm Confused (Frost Damage)

Did you cover yours? This is so odd. Maybe something in the cover itself? Low of 38 and the neighbor is 100% fine, but you're all dead again? You got a mortal enemy with a Round-Up fetish?

SOB
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Re: I'm Confused (Frost Damage)

No, I did not cover mine. I think it got colder than 38 actually. In fact, I know it did but I don't know exactly how cold it got. That morning my thermometer read 36. I have since moved it out to the garden to get a more accurate reading out there.

Funny you ask about the enemy...my other neighbor and I did get into a spat just before all these frosts hit :shock: From my experience though round-up makes the vegetation turn yellow and die. Everything turned almost black and wilted before dying.

It also dawned on me that I did use my round-up sprayer (which I clean after each use) to spray Dipel for controlling cutworms. But, again, things didn't yellow. Also, I sprayed all my onions and they are still growing just fine. I will, however, buy a new sprayer that is just for garden spraying and will never have round-up in it.

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