Second layer of plastic and frost cover? - Page 2

FourOaks · February 8, 2018

Well.. yeah.

Didnt think about the condensation factor.

bower · February 8, 2018

For night covering only, I would get the cheapest and heaviest row cover available. Our Dollar Stores regularly carry the stuff I described. Not useful outdoors but fine in the greenhouse. The nominal value of a 2 oz Agribon ("50") is something like 10 degrees of protection iirc. Just put the cover on before temperatures drop to a critical point after sunset, they'll hold the warmth nicely.

I have used the painter drop sheets as well. And I've combined plastic drop sheet with row cover - this didn't work well for me. Condensation on the plastic, then the fabric touching it gets wet.

Cole, I'm surprised you've never tried the ag fabrics. They are not only for use on the ground, and the professional grade fabrics can have higher thermicity than poly. The Agryl site is pretty cool, check out the 'micro tunnels' for tomatoes.

http://www.agrylnovagryl.com/applica...o-tunnels.html

FourOaks · February 8, 2018

Quote:

Originally Posted by bower

For night covering only, I would get the cheapest and heaviest row cover available. Our Dollar Stores regularly carry the stuff I described. Not useful outdoors but fine in the greenhouse. The nominal value of a 2 oz Agribon ("50") is something like 10 degrees of protection iirc. Just put the cover on before temperatures drop to a critical point after sunset, they'll hold the warmth nicely.

I have used the painter drop sheets as well. And I've combined plastic drop sheet with row cover - this didn't work well for me. Condensation on the plastic, then the fabric touching it gets wet.

Cole, I'm surprised you've never tried the ag fabrics. They are not only for use on the ground, and the professional grade fabrics can have higher thermicity than poly. The Agryl site is pretty cool, check out the 'micro tunnels' for tomatoes.

http://www.agrylnovagryl.com/applica...o-tunnels.html

Good point. Introducing the plastic would/could easily encourage humidity. Which at those potential temps could be dangerous.

Im now really thinking that the covers would be the way to go on seedlings that could tolerate cooler temps. Other seedlings though will have to have some kind of heat. Thats ok, as I can reduce the size of bench area that will be heated.

Interesting link.

Cole_Robbie · February 8, 2018

It's neat stuff, Bower, but I don't see any pics of greenhouse benches being covered with it. It looks like the product of choice for almost any other use, though. The earth is constantly giving off small amounts of heat, at least when unfrozen, and that is the difference between the ground and a bench of containers.

I don't think a fabric that can 'breathe,' so to speak, can have an r-value, or much of one, but yet that breathing trait makes it superior to poly as a plant cover outside or in a high/low tunnel. The earth gives off humidity, too, as do plants, and that moisture needs to go somewhere.

FourOaks · February 8, 2018

So then I wonder, would I be better off to put those flats, on the ground? Both High Tunnels have black ground cover, which should help the ground to absorb some heat during the day.

I might just have to order some cover, set it up, on the ground and on the bench, and take some measurements. To see which is better.

Hmm... the tangled web we weave.

bower · February 8, 2018

Hmmm... I don't understand the notion that the ground is the source of heat and the fabric can't work without it. Solar heat warms the air in the greenhouse and the soil or other media your seedlings are growing in, whether they're on a bench or on the ground. Row cover keeps the warmth from escaping at night.. We use it over seedlings on benches at the farm as well as on the ground. I saw no sign it wasn't working when they were raised off the ground.

One thing I do in my own greenhouse is to use water buckets (tightly sealed) for heat mass. I also have used a couple of planks laid over several sealed 5 gallon buckets as a bench for the seedlings. So that is one way to add heat storage mass and minimize heat loss under cover.

Why the seedlings are up off the ground, I have checked it with my thermometer and it gets a lot colder on the ground at night than it does up on a bench. Cold air sinks. And in spring, there's really no heat left in the storage mass of the floor.. nor much in the earth if it comes to that.

Here's a link to the selection at Harris Seeds - I notice they have a 4 oz and a couple of others on sale at the moment - also they have a good variety of shapes and sizes. I wouldn't mind getting a wider piece for my "top" instead of joining 2 pieces.
https://www.harrisseeds.com/collections/row-covers

FourOaks, there are good prices on Dupont row covers at Walker Plants in NC. They're in your area and would know your conditions well.
https://www.walkerplants.com/accesso...row-covers.htm

bower · February 8, 2018

Quote:

Originally Posted by Cole_Robbie

I don't think a fabric that can 'breathe,' so to speak, can have an r-value, or much of one, but yet that breathing trait makes it superior to poly as a plant cover outside or in a high/low tunnel. The earth gives off humidity, too, as do plants, and that moisture needs to go somewhere.

Aha

You need a piece of the stuff to play with Cole. It does breathe - but not as much as you think. Humidity and heat are trapped inside pretty well in spite of the (very small) pores in the fabric that breathe. It makes amazing seedbed cover - perfect conditions for germination. The 'breathing' is only enough that it doesn't collect condensation or turn into a cooker. Warm and moist but not drippy. The thickness of the fabric and fineness of the fibers seems to tune the flow of heat and moisture pretty perfectly...

Different weights work differently too, I have to say, and quality varies a lot. I have a bunch of cover which I got from the farm when they replaced theirs and were throwing it away. Yes the pieces were torn in places and dirty but lots of good stuff for a garden of my size. And the quality is really nice compared to the Dollar Store stuff. I washed a bunch of it and it was perfectly good for my needs, still using after 3 years or more... (no, tatters don't bother me

)

FourOaks · February 8, 2018

Bower, your benches, are they solid? Or are they more like mine, with lattice on top?

Might have to order from Harris. Thanks for that...

bower · February 8, 2018

My benches are planks and buckets or whatever small tables etc mostly solid. At the farm we had seedlings in 1020 trays on top of some kind of screen thing laid up on sawhorses, another one was across some cinder blocks iirc. The row cover was over the top and tucked underneath around the sides.

bower · February 8, 2018

Here is some interesting data, from a field trial overwintering low tunnels in Massechussetts with different covers and combinations. The best figures are a combination of greenhouse plastic and row cover. I'm not sure if the row cover is inside or outside.

From this pdf:
https://ag.umass.edu/.../extending_v...shey_final.pdf
sorry that link doesn't work, the title is: Extending Vegetable Harvest and Sales Using Tunnels, Row Covers and Winter Storage
UMass 2014

clkeiper · February 8, 2018

Quote:

Originally Posted by FourOaks

So then I wonder, would I be better off to put those flats, on the ground? ....

Hmm... the tangled web we weave.

I have lost a lot of plants to pill bugs by putting flats on the ground...even with ground cover inside the greenhouse. they have nothing else to eat and will devour anything they can reach.

FourOaks · February 8, 2018

Quote:

Originally Posted by bower

Here is some interesting data, from a field trial overwintering low tunnels in Massechussetts with different covers and combinations. The best figures are a combination of greenhouse plastic and row cover. I'm not sure if the row cover is inside or outside.

From this pdf:
https://ag.umass.edu/.../extending_v...shey_final.pdf
sorry that link doesn't work, the title is: Extending Vegetable Harvest and Sales Using Tunnels, Row Covers and Winter Storage
UMass 2014

I googled that and found the PDF. Looks like to get those results, they used 1.25 oz cover. Page 13.

Im guessing, they put the cover on top of the plants, then covered the hoops with plastic.

Quote:

Originally Posted by clkeiper

I have lost a lot of plants to pill bugs by putting flats on the ground...even with ground cover inside the greenhouse. they have nothing else to eat and will devour anything they can reach.

Touche'

Dont need critters eating my potential profit. Have enough problems with ground hogs eating my beans.

FourOaks · February 8, 2018

Quote:

Originally Posted by Cole_Robbie

..but I don't see any pics of greenhouse benches being covered with it.

Something just occured to me. I recall seeing the outdoor plants have been covered with Row Cover/Frost Blanket at the Big Box Store.

They have metal ventilated benches, with pvc hoops.

Grant it, they have all that concrete too.

But I dont imagine all that concrete does that much for the plants, because of the windchill factor. My guess would be that any blowing wind would counter heat that radiates from within.

Cole_Robbie · February 8, 2018

Bower is cheating with all those water buckets!

LOL - just kidding. I do the same thing with horse troughs full of water, or at least am much as I can. I have never seen mass used under benches on a commercial scale. It might be difficult to do in a cost-effective manner. And it's the same with anything that costs more, it might work better on a smaller scale, but not translate well to a larger scale.

FourOaks · February 9, 2018

Well, heres an interesting observation.

I got up this morning at 6:45. Temp in the "Seedling House" was a balmy 27 degrees, with 90% RH. This is according to a wireless Accu Rite Thermometer. I placed the transmitter on the bench where the seedlings were.

At 7:50 the temp creeped up to 31 degrees, and still holding at 90% RH.

On a whim, and I wish I had thought about it sooner, I went out and moved the transmitter to the ground.

I came back in the House and noticed on the receiver that it indicated the temp was now 32 degrees.

That could just be from touching the unit.

But then just a few minutes later, it went up a couple more degrees. And the RH went down 1%

Now, it has been 23 minutes, and the temp is 40 degrees, with an RH of 88%

A couple points to keep in mind. The sun is shining, but there is a heavy frost on the plastic, blocking the sun.

I just looked and now its 41 degrees.

I think this is going to need some repeated tests.

February 8, 2018	#21
bower Tomatovillian™ Join Date: Feb 2012 Location: Newfoundland, Canada Posts: 6,794	Hmmm... I don't understand the notion that the ground is the source of heat and the fabric can't work without it. Solar heat warms the air in the greenhouse and the soil or other media your seedlings are growing in, whether they're on a bench or on the ground. Row cover keeps the warmth from escaping at night.. We use it over seedlings on benches at the farm as well as on the ground. I saw no sign it wasn't working when they were raised off the ground. One thing I do in my own greenhouse is to use water buckets (tightly sealed) for heat mass. I also have used a couple of planks laid over several sealed 5 gallon buckets as a bench for the seedlings. So that is one way to add heat storage mass and minimize heat loss under cover. Why the seedlings are up off the ground, I have checked it with my thermometer and it gets a lot colder on the ground at night than it does up on a bench. Cold air sinks. And in spring, there's really no heat left in the storage mass of the floor.. nor much in the earth if it comes to that. Here's a link to the selection at Harris Seeds - I notice they have a 4 oz and a couple of others on sale at the moment - also they have a good variety of shapes and sizes. I wouldn't mind getting a wider piece for my "top" instead of joining 2 pieces. https://www.harrisseeds.com/collections/row-covers FourOaks, there are good prices on Dupont row covers at Walker Plants in NC. They're in your area and would know your conditions well. https://www.walkerplants.com/accesso...row-covers.htm Last edited by bower; February 8, 2018 at 06:53 PM. Reason: add

February 8, 2018	#16
FourOaks Tomatovillian™ Join Date: Mar 2016 Location: NC Posts: 511	Well.. yeah. Didnt think about the condensation factor.

February 8, 2018	#19
Cole_Robbie Tomatovillian™ Join Date: Jun 2012 Location: Illinois, zone 6 Posts: 8,407	It's neat stuff, Bower, but I don't see any pics of greenhouse benches being covered with it. It looks like the product of choice for almost any other use, though. The earth is constantly giving off small amounts of heat, at least when unfrozen, and that is the difference between the ground and a bench of containers. I don't think a fabric that can 'breathe,' so to speak, can have an r-value, or much of one, but yet that breathing trait makes it superior to poly as a plant cover outside or in a high/low tunnel. The earth gives off humidity, too, as do plants, and that moisture needs to go somewhere.

February 9, 2018	#30
FourOaks Tomatovillian™ Join Date: Mar 2016 Location: NC Posts: 511	Well, heres an interesting observation. I got up this morning at 6:45. Temp in the "Seedling House" was a balmy 27 degrees, with 90% RH. This is according to a wireless Accu Rite Thermometer. I placed the transmitter on the bench where the seedlings were. At 7:50 the temp creeped up to 31 degrees, and still holding at 90% RH. On a whim, and I wish I had thought about it sooner, I went out and moved the transmitter to the ground. I came back in the House and noticed on the receiver that it indicated the temp was now 32 degrees. That could just be from touching the unit. But then just a few minutes later, it went up a couple more degrees. And the RH went down 1% Now, it has been 23 minutes, and the temp is 40 degrees, with an RH of 88% A couple points to keep in mind. The sun is shining, but there is a heavy frost on the plastic, blocking the sun. I just looked and now its 41 degrees. I think this is going to need some repeated tests.