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Raised beds and frost

Posted by aliweed 5 (Ely, IA) (My Page) on
Tue, Apr 28, 09 at 14:34

I am assuming that my raised 12" raised beds have higher soils temps than the ground that I planted in last year (same located, new beds). I was wondering if the height of the beds makes them less susceptible to frost as well. Is it likely that the grass near my beds could be covered in frost while the plants in the raised beds are not? My raised beds are also located on a hill that gets a fair amount of wind which might make frosts less likely too.

I guess I am asking if it is reasonable to assume that the micro-climate of my garden might allow me to plant a week or two earlier than the May 15 last frost date. I plan on testing this out, but want to know if any one has any thoughts or experience.

I will post a link to a blog with some pictures.

Here is a link that might be useful: garden blog (with pictures)


Follow-Up Postings:

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RE: Raised beds and frost

I was wondering if the height of the beds makes them less susceptible to frost as well.

Not more than a few inches above the surface.

You will certainly have a different microclimate and the beds will heat up sooner than flat ground. The issue is whether this additional heat will translate up, say, 6 - 12" from the soil surface to ward off frost sufficiently to prevent damage.

My large raised veggie bed against the house (much larger than most) does not allow me to plant without protection. I have walls o' water and hoops out now, and we had ~4" of snow two days ago. It allows me to start earlier, however, as the soil temps are warmer. But I still must protect.

HTH.

Dan


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RE: Raised beds and frost

I agree with Dan, and would like to add a few things.

The location of your beds only allow your soil to become warmer - not the air that the foliage of your plants are exposed to.

Speaking from a psychrometrics standpoint, air always contains grains of moisture within it - and this is where frost actually comes from. When the correct combination of dewpoint, grains of moisture, and ambient temperature come together - frost forms on the foliage of plants, which in turn - freezes the water that's in the plant's cells.

EG


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RE: Raised beds and frost ii

The location of your beds only allow your soil to become warmer - not the air that the foliage of your plants are exposed to.

OK, I have the geek self-limiter switch turned on.

This is true in free air. I trap the radiating heat with hoops holding plastic or/and row cover, which raises the temps under the hoops.

The additional heat of the beds allows me to efficiently trap heat this way, and when I'm really frisky I put water jugs filled with colored water under the hoops for more heat. This year I've been traveling so I haven't done the jug thing due to the schedule.

[/geek self-limiter switch]

Dan


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RE: Raised beds and frost

Thanks so much for the insight. You have given me a few things to think about. I will probably try and be patient and keep everything in the cold frame for a bit longer.

Thanks again


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RE: Raised beds and frost

Dan, that was funny....I only get geeky once in a while, the rest of the time I'm all redneck! Ha!

aliweed - you're welcome.

EG


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RE: Raised beds and frost

  • Posted by peel z6 CT (My Page) on
    Tue, Apr 28, 09 at 20:16

Dan, I'm probably just dense, but why colored water?


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RE: Raised beds and frost

I used Dan's dark water idea and it raised the temps under the plastic hoop cover by about 10 degrees or so most nights compared to the temps with plastic alone.

Here is a link that might be useful: Tales of a Transplanted Gardener


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RE: Raised beds and frost

Dark colors absorb more solar heat than lighter colors, peel, and in this instance, clear water. Look around and get a good price on cheap food dye and fill up a couple of gallon milk jugs (or more expensive but more space-efficient are those 2.5 gal flat rectangle water containers you put in your refrig).

I did this in my cold frame here in Denver last year and had cool season veggies all winter (but it is sunny here most days - IA might be a different story). Still doing garden trials for a solar soil heater using this principle.

10 is pretty good, greenbean. I'll do that this fall with a max-min thermometer and see what I get.

Dan


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RE: Raised beds and frost

I also have some dark stones in there but I think I had the stones in for a while before I added the water and didn't notice much difference. I had a string of lights in there for a while but only plugged them in 2 or 3 nights when it got REALLY cold (10 or 15 deg I think).

I have one of the remotes for the wireless thermometer hanging from one of the hoops so I can check it from my living room and compare it to the one by the back door.


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RE: Raised beds and frost

My cold frame is too far away from a plug for lights. I used two candles in the coldframe last winter for several nights when the temps plunged below zero F (likely the same nights you had). In the mornings, I can tell the water jugs are still radiating heat, but the bricks I had in there for a while were played out and at ambient temp.

Which brings me back to the OP - my very large raised bed did not freeze appreciably last winter and when it did briefly it heated up quickly and thawed (I'm at a sunny 5700 ft, tho).

Dan


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RE: Raised beds and frost

How many milk jugs would you put in an 8x4 wooden (with plexiglass) coldframe to keep things nice and cozy? I have had plants in there for a month and things look great, but I would love to really extend the season in the fall if I could. Pictures of my coldframe can be found on my blog.

Here is a link that might be useful: Blog (coldframe pictures)


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RE: Raised beds and frost

Only one layer of transparent material? You want two for the dead air space, adding that gave me 8-10. I have a 4x6 that had 4 gallon jugs in it, & I'd cover if it went below, say, 20F during Jan-Feb.

Dan


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RE: Raised beds and frost

Wow Dan that is a great idea!! Colored water, that would never have occurred to me.


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