Author Topic: Unconventional super-insulated Cold Frame idea  (Read 3098 times)

nereo

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Unconventional super-insulated Cold Frame idea
« on: February 04, 2022, 09:27:53 AM »
Synopsis:  I'm toying with building a highly unconventional "insulated cold-frame" with off-cuts I've collected.  I'm soliciting feedback on whether this is a good or terrible idea, and problems I might not have considered.

I live in northern New England and have long thought about making a few 'cold-frame' boxes to extend the growing season by ~6 weeks on each side. Recently my workplace has undergone a very large renovation project, and I've been collecting the 'leftovers', including some very large insulated panels and a bunch of polycarbonate greenhouse sheets  Now I *think* I have the materials to make a truly epic cold-frame, but since no one builds cold-frames this way, I can't find much info.

To be clear one would never build a cold-frame this way if they had to pay for these materials - the insulated panels are prohibitively expensive (each full-sized panel costs >$1,000... even the offcuts represent a few hundred each in material)- but these are just off-cuts destined for the landfill. It sickens me how wasteful the construction industry is.

Materials:
Walls - (sunk at least 24" into the soil... maybe deeper): 6" thick insulated panel off-cuts from our walk-in freezer.  Both sides are stainless and food-grade. I've got 4' x 4' offcuts, as well as some 4' x 6' offcuts. Should give the walls an R-23 with no thermal bridging (which I know is insane for an insulated cold frame.  Most seem to use an inch or two of XPS foam at most).

Roof: Triple-wall polycarbonate greenhouse panels (10mm), sloped ~15 degrees and hinged on one side.  Again, these are offcuts and way, way overkill, but it's way I've got.

Design:
Largely the classic cold-frame shape with a sloped roof and southern facing, but with insulated walls. The footprint would be either ~4' x 6' or (if I decide to do more cutting) 3' x 4').  I like the 3' wide for accessibility (with the 'roof' it's very hard to the back wall of a 4' deep bed) but it involves more work (cutting) and I might benefit from the volume-to-perimeter of the larger frame.  Dunno.  Cutting these panels is a bear, as they have metal on both sides).  I have a spot in my yard that should get 6+ hrs of direct sunlight on March 1st and October 1st. My hope is I can keep the soil temp warm enough to have frost-tolerant greens in March-May and again in Sept - mid November. The personal-value of having fresh-picked greens in the extreme shoulder season is the entire reason for this project. FWIW our "frost-free date is May 16th and we typically get our first snows in early October. Also, I've accepted that this frame will likely not be used during June-Aug as it'll probably get too hot (even with the roof off).  That's ok as we'll have lots of other beds.

With such large and well insulated panels I could bury the panels 24" (or should they be 36"?) into the soil to form the box, and then have a foot (or more) of good soil above ground. Having the panels so deeply buried and so well insulated should (i think) allow the soil to not freeze during even hard frost events and night-time temperatures into the upper teens (~-10ºC). 

Questions:
I'm worried about frost depth and whether this will "upheave" the cold-frame each year.  On one hand our frost depth is ~52" here (can't go that deep!) but OTOH with the cold frame in place I think the frost won't ever reach more than 12" inside the frame (probably less) in the coldest months.  I'm not sure how it works around the exterior.  I guess I can just try and see.  I might be able to mitigate this by mulching heavily around the edges...

drainage - I know I want ground-contact.  Right now I think I might add a layer of coarse sand directly on the earth, and then fill with my soil to a depth of 8-12". I guess drainage isn't a big problem since I will completely control the watering schedule.

venting - simplist solution is just to lift the lid on hot days and prop it open with a stick.  But I know me, and know I'll either forget or be out of town. So I might try one of the auto-vents common on greenhouses that rely on the expansion of wax to open/close.  Looks like I could get one for about $35, so worth a try?

air-exchange. With these panels and a too-tight fitting roof I run the risk of having too little air exchange. Not sure if this will be important on a practical level or not.

herbgeek

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Re: Unconventional super-insulated Cold Frame idea
« Reply #1 on: February 04, 2022, 09:54:39 AM »
Sounds like a lot of work, and a high risk of frying anything in side.   Definitely get the automatic arm.

I get a couple of months of growing on either side of the season (I'm in MA) with much less work and expense.  I put up low tunnels- PVC conduit covered with uv stabilized plastic sheeting (important to use uv stabilized if you want to use the plastic more than one season), and attached with clips.  The conduit is held to the ground with 1 foot sections of rebar (got at Home Depot for a dollar each).  The conduit cost $25 for 100 feet,  the clips were maybe 50 cents or a dollar a piece (you could also use sandbags on the side instead) and I forgot how much the plastic was but I've reused it for like 10 years now.   

The conduit is cut to 5 foot lengths and the ends are spaced maybe 3 foot across.   I space the conduit  hoops about 18" apart to handle any snow load (but if there is a lot of snow, I do clear any excess off).

 I put up the hoops in the fall without the plastic.  Around March 1 I attach the plastic and let the soil warm for the month of March.  At the end of March or beginning of April, I put in lettuce starts.  In the fall I've been able to keep plants alive until Christmas.   Very low tech, very effective, fairly inexpensive.
« Last Edit: February 04, 2022, 10:03:40 AM by herbgeek »

Frugal Lizard

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Re: Unconventional super-insulated Cold Frame idea
« Reply #2 on: February 04, 2022, 10:07:51 AM »
I am totally jealous of the riches you have.

Not an expert on frost penetration. But in my experience, the biggest problem with frost is when the material doing the moving can't withstand the movement and cracks at a weak point.  If your method of construction has give points to absorb the stress, the whole system can move around as needed - and stretch and compress. Some flexible material at the corners that can take low temperatures?
The heat of the inside will reduce frost - as will a bale of straw around the perimeter - or gasp - extra rigid insulation laid horizontally around the exterior at a depth just below a "mulch" path around the cold frame.  You could google the angle that the frost will slide around the insulation - but offhand I think it is 1:1

You may want to paint the interior a dark colour to have some sort of heat absorbtion.
Venting is essential - and automatic ones from the greenhouse trade are excellent - I did pay 95$ Canadian for the four I bought for my neighbours greenhouse.
Some air change is good particularly when you can have heavy condensation inside and develop ripe mold conditions.  A little movement also strengthens up the plant stems and gives an overall sturdier plant.

Drainage: remove any compaction in the soil bed and ensure that the planting bed isn't a tea cup.  Top dress with lots of organic material as all the no-dig gardeners recommend.

Nikki Jabbor has a great book:  Growing Under Cover that may cover questions better than I.

Dicey

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Re: Unconventional super-insulated Cold Frame idea
« Reply #3 on: February 04, 2022, 10:18:38 AM »
Nothing of value to add, just want to come along for the ride. Go, nereo!

nereo

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Re: Unconventional super-insulated Cold Frame idea
« Reply #4 on: February 04, 2022, 10:46:07 AM »
Sounds like a lot of work, and a high risk of frying anything in side.   Definitely get the automatic arm.

I get a couple of months of growing on either side of the season (I'm in MA) with much less work and expense.  I put up low tunnels- PVC conduit covered with uv stabilized plastic sheeting (important to use uv stabilized if you want to use the plastic more than one season), and attached with clips.  The conduit is held to the ground with 1 foot sections of rebar (got at Home Depot for a dollar each).  The conduit cost $25 for 100 feet,  the clips were maybe 50 cents or a dollar a piece (you could also use sandbags on the side instead) and I forgot how much the plastic was but I've reused it for like 10 years now.   

The conduit is cut to 5 foot lengths and the ends are spaced maybe 3 foot across.   I space the conduit  hoops about 18" apart to handle any snow load (but if there is a lot of snow, I do clear any excess off).

 I put up the hoops in the fall without the plastic.  Around March 1 I attach the plastic and let the soil warm for the month of March.  At the end of March or beginning of April, I put in lettuce starts.  In the fall I've been able to keep plants alive until Christmas.   Very low tech, very effective, fairly inexpensive.

I’m not sure I agree/understand your assessments of it being more work and cost. It certainly would be extraordinarily expensive if I were to buy these materials, but I already have them.  In effect it’s “use them or toss them”. If I didn’t have these things I might try something closer to what you have done, but I’m trying to be resourceful with what I have and not buy a bunch of plastic sheeting (conduit I have).

As for work - the brilliant things about these panels is they are designed to slot together. I can build the actual ‘frame’ in a fraction of the time that it would take me to build out of timber.

It’s great to hear you’ve been able to keep plants alive until Christmas. My dream is a thanksgiving meal which includes stuff from our garden - being a fair bit further north than you I think that’s still a not unreasonable goal.



Not an expert on frost penetration. But in my experience, the biggest problem with frost is when the material doing the moving can't withstand the movement and cracks at a weak point.  If your method of construction has give points to absorb the stress, the whole system can move around as needed - and stretch and compress. Some flexible material at the corners that can take low temperatures?

The heat of the inside will reduce frost - as will a bale of straw around the perimeter - or gasp - extra rigid insulation laid horizontally around the exterior at a depth just below a "mulch" path around the cold frame.  You could google the angle that the frost will slide around the insulation - but offhand I think it is 1:1

You may want to paint the interior a dark colour to have some sort of heat absorbtion.
Venting is essential - and automatic ones from the greenhouse trade are excellent - I did pay 95$ Canadian for the four I bought for my neighbours greenhouse.
Some air change is good particularly when you can have heavy condensation inside and develop ripe mold conditions.  A little movement also strengthens up the plant stems and gives an overall sturdier plant.

Drainage: remove any compaction in the soil bed and ensure that the planting bed isn't a tea cup.  Top dress with lots of organic material as all the no-dig gardeners recommend.

Nikki Jabbor has a great book:  Growing Under Cover that may cover questions better than I.


I’ll see if I can get the book and check it out.

One nice thing about the panels is the adhesion remains flexible at normal freezer temps (-20ºC) so it should be able to move nad flex as you described. I’m feeling better about that. And the foam around the parameter isn’t a bad idea either.  ARound here a lot of people build their decks this way, with shallow pre-cast footers sitting above compacted gravel and foam. It’s not strictly code but it’s so common most just shrug and accept it, because when done right (appropriate depth and horizontal coverage) it works just fine.

Hmm… heavy condensation leading to mold is one thing I’ll need to be watchful of. Venting will be key.  Nice to know so many have had positive experiences with auto vents

Tom Bri

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Re: Unconventional super-insulated Cold Frame idea
« Reply #5 on: February 04, 2022, 11:36:53 AM »
Sounds like a fun project. Your area is a bit colder than mine, in N Illinois, but I can tell you that the simplest 'cold frame' extends my greens into December. Last year was a normal winter and we got greens into the first week, this year was much warmer than normal and greens survived almost to Christmas.

I used nothing but a clear plastic painter's drop cloth to cover a bed 5' wide by 15' long, with the edges held down with earth along the back edge and chunks of wood along the front and sides. It is about 2' high in the center and slopes down to both edges.

Thinking about frost heaving, maybe you could pack a layer of straw or similar material around the bottom and edges to allow space for the ground to move.

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Re: Unconventional super-insulated Cold Frame idea
« Reply #6 on: February 04, 2022, 12:45:24 PM »
I like to think some 6 mil plastic or similar on the exterior side would allow some soil movement separate from the panels you are burying. Maybe tape it on the outside of the panels then backfill the exterior.

Digging 24" deep sucks.  I dig in the nicest sand you can imagine and it still is a lot of work.  I wouldn't go deeper.  If I thought I was going to 3 feet, I am positive I would change plans once I got to 2 feet (I'd say "this actually looks good").  Unless you are going to 4 feet it doesn't make a difference.

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Re: Unconventional super-insulated Cold Frame idea
« Reply #7 on: February 04, 2022, 01:58:35 PM »
Nikki Jabbor is eating out of her garden year round in Nova Scotia.....

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Re: Unconventional super-insulated Cold Frame idea
« Reply #8 on: February 04, 2022, 08:36:28 PM »
If you want ideas of what vegetables and varieties will do well in Maine winters check out Eliot Coleman. His Winter Harvest Handbook is great. He seems to experiment continually but in that book he uses high tunnels plus row covers. If you do a solar greenhouse plus row covers you should be able to grow even more than he does.

I think it's in his book that really what he's doing to harvest year round is starting growing late in season and delaying harvest/ keeping things alive until needed in winter.

RetiredAt63

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Re: Unconventional super-insulated Cold Frame idea
« Reply #9 on: February 05, 2022, 06:28:13 AM »
I think it's in his book that really what he's doing to harvest year round is starting growing late in season and delaying harvest/ keeping things alive until needed in winter.

There isn't enough light (days are too short and sun is too low on the horizon) to have things really grow in winter.  So yes, basically get them to harvest-able size by late fall and just keep them going after that.

nereo

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Re: Unconventional super-insulated Cold Frame idea
« Reply #10 on: February 05, 2022, 06:36:20 AM »
I think it's in his book that really what he's doing to harvest year round is starting growing late in season and delaying harvest/ keeping things alive until needed in winter.

There isn't enough light (days are too short and sun is too low on the horizon) to have things really grow in winter.  So yes, basically get them to harvest-able size by late fall and just keep them going after that.

This is what I’m worried about going past November. I can get 6 hours of direct sun in October, but around the winter solstice it’s going to be closer to 3 (partly because the days are so short and partly because the sun angle puts it behind some trees for most of the day.  We only get 8 hours total of daylight around the holidays.


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Re: Unconventional super-insulated Cold Frame idea
« Reply #11 on: February 05, 2022, 08:56:45 AM »
I think it's in his book that really what he's doing to harvest year round is starting growing late in season and delaying harvest/ keeping things alive until needed in winter.

There isn't enough light (days are too short and sun is too low on the horizon) to have things really grow in winter.  So yes, basically get them to harvest-able size by late fall and just keep them going after that.

This is what I’m worried about going past November. I can get 6 hours of direct sun in October, but around the winter solstice it’s going to be closer to 3 (partly because the days are so short and partly because the sun angle puts it behind some trees for most of the day.  We only get 8 hours total of daylight around the holidays.

It isn't a problem, really you just plan around it.  Expect everything to just sort of hibernate from say mid-November to mid-February.   I've never done it, but the recommended books will be full of advice on what to grow and how to maintain and harvest it.

Light is always the issue anyway.  What plants will do well in the light available for a garden.  Where is there enough light for vegetables and ornamentals that need full sun.  Houseplants need to be in the appropriate window or have supplemental lighting.  Commercial greenhouses that grow all winter have supplemental lighting.

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Re: Unconventional super-insulated Cold Frame idea
« Reply #12 on: February 06, 2022, 07:54:12 PM »
I guess I wonder how deep the walls need to go to keep the ground warm enough for growing. If Coleman can do it with hoop houses, and a bit of solar gain, I wonder.

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Re: Unconventional super-insulated Cold Frame idea
« Reply #13 on: February 06, 2022, 11:08:53 PM »
When I was in Iceland I saw all their greenhouses. So many! They grow bananas. They have no trouble with heat, because there is so much thermal energy, and I think it was 80% of houses have hot water pumped in so they don’t need their own water heaters.

There are quite a few vegetables that are shade tolerant - mainly leafy greens (non heading lettuce, endive, Chinese cabbage and other Chinese greens). You wouldn’t want to be growing plants that require pollination anyway, unless you’re doing starts.

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Re: Unconventional super-insulated Cold Frame idea
« Reply #14 on: February 07, 2022, 12:34:17 AM »
How will you solve heat loss through the roof, especially during nighttime?

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Re: Unconventional super-insulated Cold Frame idea
« Reply #15 on: February 07, 2022, 06:40:50 AM »
I know this doesn’t apply directly to your situation, but on talking about frost heave, take a look at frost protected shallow foundations. 

I’m this application, you can raise the “frost line” around your structure without getting down the 36-42” likely needed in your location.


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Re: Unconventional super-insulated Cold Frame idea
« Reply #16 on: February 07, 2022, 07:09:03 AM »
@gaja - some extra insulation for the night time can be an insulated tarp on top or snow or straw / floating row covers inside the cold frame.




nereo

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Re: Unconventional super-insulated Cold Frame idea
« Reply #17 on: February 07, 2022, 09:15:52 AM »
How will you solve heat loss through the roof, especially during nighttime?

The short version is you don't avoid heat loss, but inside the cold frame stays warm due to 1) thermal mass and 2) a lack of convection.  The lid also has some insulation (I think it's like an R~2).

The dirt inside heats up during the day time.  Depending on your crops you want it to be somewhere between 50-75ºF, though many frost-tolerant varieties will do just find until just above freezing.  Even at moderate temperatures that dirt (several hundred pounds of it in a 3x8' frame) holds a ton of thermal energy, which it slowly releases at night. 

The other thing that massively helps is the lid which [nearly] stops convection (air currents).  Without those convection sells heat loss is a fraction of what it otherwise would be. 

Some people will extend cold-frame growing into very very cold temperatures by tossing blankets or hay over the top at night. 

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Re: Unconventional super-insulated Cold Frame idea
« Reply #18 on: February 07, 2022, 05:35:58 PM »
Quote
How will you solve heat loss through the roof, especially during nighttime?
Some folks use Christmas tree lights, the old incandescent ones.  The newer LED ones are too efficient and don't heat up.  In the past I've used a soil cable for heating.

nereo

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Re: Unconventional super-insulated Cold Frame idea
« Reply #19 on: February 07, 2022, 06:00:15 PM »
Quote
How will you solve heat loss through the roof, especially during nighttime?
Some folks use Christmas tree lights, the old incandescent ones.  The newer LED ones are too efficient and don't heat up.  In the past I've used a soil cable for heating.

I’ve always heard of cold-frames as being passive, and those with supplemental heating (either using the old christmas-lights or more modern soil cables) as “hotbeds”.

Cold frames (sans external heat) can still grow veggies even when there is snow on the ground. 

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Re: Unconventional super-insulated Cold Frame idea
« Reply #20 on: March 19, 2022, 02:02:15 PM »
Eliot Coleman who grows year round on Penobscot Bay has a great website with lots of stuff on cold frames: www.fourseasonfarm.com.

nereo

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Re: Unconventional super-insulated Cold Frame idea
« Reply #21 on: March 19, 2022, 02:30:59 PM »
Thanks for the link, definitely worth me exploring more as it’s the same region as where I am

Not much of an update to give as the ground has just begun to un-freeze. I’ve got the materials and my plan is to have the cold frame operational by September for a fall seeding of greens which hopefully will carry into December. Then we will see how it’s going

Tom Bri

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Re: Unconventional super-insulated Cold Frame idea
« Reply #22 on: March 20, 2022, 03:17:21 PM »
Pulled off the plastic tarp a few days ago. Several greens actually survived and are growing. Arugula and other related greens.
So the simplest cold frame not only gives you late fall greens, but also early spring. I stopped picking in mid December and can start picking now.

 

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