Greenhouse tricks

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The double thick skin 16mm Clear Polycarbonate Sheet with 5 Walls and UV protection - ePlastUSA is better but here is normal sheeting

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Undersoil fans are a must for geothermal like these Geothermal Greenhouse and Undersoil Ventilation Systems

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Thanks for these. Greenhouses are a black hole when it comes to forums, and advice. I think there just aren’t enough hobby greenhouse owners to support such a thing. When I first set mine up I tried very hard to find something, anything to help. In the end I turned to books. Was like the old days before the Internet!

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You know, since I saw the post from Bernie yesterday, it made me stare to think about making geothermal heat loops for a greenhouse. In the long run it would make sense to run a tiny fan to circulate cold/warm air (relative to the season) and in a smaller structure you wouldn’t need a huge loop, especially if you were just trying to mitigate extremes.


I think you may be right about a simple geothermal loop. But if you are placing much credence on Bernie’s post I’d pump the brakes. An 8 inch hole in the ground isn’t going to supply enough heat to warm anything. I’m sorry I’m not buying that. Any heat advantage in his system is coming from elsewhere.

In terms of greenhouse coverings I think woven coverings are a real competitor to the multiwall polycarbonate. I’m talking Solarig and Palring: Greenhouse covers and ground covers (

For me double inflated Solarig has lasted 3x as long as the normal 6 mil GH poly and it’s a fraction of the price of multiwall polycarb. It’s heat holding ability compared to polycarb sheets is enhanced by having no seams. So it’s more air tight.

The most impressive GHs I’ve seen for cold climates didn’t have an air circulating geothermal system. Instead they were underground or had thick earth berm walls. Just doing that with a Solarig roof would gain 2-3 zones in hardiness. Instead of an 8 inch hole down to the frost line have the whole GH below frost line.

If I built another GH here it would be below ground with the only covering being a double inflated Solarig roof and south wall. North, east, and west walls would all be soil or insulated panels.


If you see this post from 2015 Oranges in Zone 5 you know what my inspiration is. @fruitnut has more experience than anyone on greenhouses The green is back in the greenhouse. Then you saw this thread Geothermal orange grove! Heavy yields! years ago which is sorta what Bernie is talking about now. Threads like this were great attempts Cattle Panel Hoophouse Greenhouse . We use simple tricks all the time Anyone avoiding the store by growing indoors, covered beds, or a greenhouse? . @fruitnut demonstrating some great greenhouse tricks Greenhouse inside a greenhouse and more A few greenhouse pictures and @Barkslip The Very Best Smaller Greenhouses Home Heater . We have done lots of zone stretching Cold hardy figs . The same ideas keep come up which is geothermal because it can buy you 20 to 30 degrees at least Pit greenhouse ideas . Imagine combining what we know with a few new tricks. What i like is as an example @Barkslip could still add geothermal to his current setup by adding some buried lines and bringing that air from the ground in Pear Dormancy in my Greenhouse: 14 cultivars 2 Rootstock . Remember below the frost line its not that cold and in the summer its not that hot. Plants wont cook or freeze if it’s done right. Here is another great greenhouse Building a Greenhouse and more discussion Greenhouse in Zone 7 and more ideas Is a small greenhouse worth the effort? . Here are more tips Greenhouse project planning . This is my all time favorite post by fruitnut Greenhouse fruit update . Temperatures are the enemy in the summer which makes simple geothermal appealing How to reduce greenhouse temperatures?

More from fruitnut

My current thoughts are to use my small cattle panel greenhouse again, geothermal, solar power. Here are a few techniques we talked about in 2018. If the green house is in close proximity to my barn and it is i add gutters and reuse rain water to stabilize the temperature inside and for plants ofcourse. Heat the barrels inside the greenhouse by painting them black or by using a solar hot water heater.


This guy in Nebraska combines a few methods Geothermal orange grove! Heavy yields! . Had good luck with a dwarf citrumelo here which came from a local nursery. Here is a video on cold hardy citrus. Wanting to try satsuma. Yuzu is very hardy and im thinking about trying it. Have grown trifoliata but they are not something i care for. They can always be grafted over if someone is growing trifoliata

“An 8 inch hole in the ground isn’t going to supply enough heat to warm anything. I’m sorry I’m not buying that. Any heat advantage in his system is coming from elsewhere.”

My data shows differently. Specifically a double wrapped insulated tarp increases the heat inside the teepee by 3C or 4C. This heat is coming up from the ground, through the snow inside the teepee (to protect the roots) and is captured inside the teepee. So at -40C it is only about -36C or -37C inside the teepee. However with a geothermal hole (9 ft. deep and 8 inches wide) in addition, I have been recording about 12C warmer inside the teepee due to heat at +5C coming up into the teepee via the stack effect.

A friend is doing this exact same test with apricots near Sundre, Alberta. He has a power auger on his skid steer and drilled a 10 foot deep hole one foot across. At -34C in the last week he reported the temperature inside the teepee was only -17C, so a 17C increase in warmth. It will be interesting to see how the data comes back in the second half of winter as the ground freezes deeper.


Hi Bernie:

17C that’s 37F for those metrically challenged. Can you tell me the approx R value of the wrapping and the dimensions of the covering? With those data I can calculate the approximate BTU coming out of your hole.

I have to input about 100,000 BTU per hour to hold my greenhouse 37F above outside with an average R value of ~ 1.8 to 2.

If your hole really works that well then put the whole orchard 8 ft underground and put an 8ft hole about every meter in all directions. Cover in winter with my woven poly. That should give you +17C all winter long, maybe more. I think it probably would.

Could you patent the hole in the ground idea for geothermal heating? It would be pretty easy to do. Dig the hole, put in a casing, and a screen on top, no fan needed.

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@fruitnut @Bernie

They have been doing this for years but the hole in the ground is usually a longer run. The guy in Nebraska did this years ago. Another gentleman named Bob Duncan in Canada began doing this about 13 years ago Geothermal orange grove! Heavy yields!

Hi Fruitnut,

A rough calculation gave 360 BTU per hour coming up the geothermal bore hole of 9 ft. deep and 8 inches wide. A 100 watt incandescent bulb gives off 341 BTU per hour. My friend with the 12 inch wide and 10 ft. deep hole should of course gather even more heat inside his teepee.

I plan to put a thin 8" wide pvc sewer pipe into the hole with about 18" of the pipe sticking above ground so the snow or dirt won’t fall back down into the hole this spring. I didn’t for this test (as I wasn’t sure it would work) and instead cut the bottom out of a 2 gallon pot and use this as a “chimney” so snow won’t fall into the hole.

But to answer your question, The teepee base is roughly 4 ft. by 4 ft, and the teepee is 8 ft. tall. The insulated tarps have 1/4" of foam insulation in them, so a double wrap would be 1/2 inch of foam or R2 insulation value. The “plug” of insulation near the top of the teepee is about 18" by 18" and is R20 pink insulation.

A chart and a formula a buddy provided for me is below. The chart doesn’t copy well, but his formula and his predicted temperatures are below. So far his predictions are pretty accurate as to the temperatures I am seeing inside the teepee with the geothermal bore hole.

y = 0.001936x2 + 0.767536x - 0.008287
R² = 0.999665
Ambient Measured Calculated
0 to -38.0 °C Temp(°C) Teepee Teepee
Ambient Air Temperature : -40 °C -22 -16 -15.9
Predicted Teepee Temp’ : -27.6 °C -31 -22 -21.9
-35.5 -24.5 -24.8
-38 -26.6 -26.4

Predicted (i.e. outside of data range)
-40.0 — -27.6
-45.0 — -30.6
(n.b., still an excellent R-squared correlation coefficient)
The data so far suggest that if it gets down to -40 C the temperature in the teepee, with the geothermal heating, will be about 12.5 C warmer, i.e., -27.6 C (the highlighted yellow values above).
Hopefully it won’t get to -45 C for you to see if the teepee is at -30.6 C (blue highlighted cells above)!


I was going to suggest for your buddy with the 12" boring capacity- 5 gallon buckets with the bottoms cut out and stack opposite ends to each other should be pretty cheap to come by as well as relatively easy to deploy, especially if he has forks or something to keep a stack and just build down the “well”. Most certainly cheaper than actual 12" pipe these days… :roll_eyes:

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It might not be legal im not sure but i suspect some tires concreted in place would be really good about 10 foot underground. Dig a trench just wide enough for the tires and stack them and stake them and dump concrete on them. Dont want anyone to just do that , check if its legal wherever you are first. There are better ways like a hollow tree cast in concrete.

Some of the well casings I’ve seen were much less involved than what you just mentioned. I don’t know that concrete would be necessary for this kind of project, however if it was me I’d absolutely find some kind of grating to place on top to limit critters (and children) falling in the holes.

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Not a trick currently available but a good one to plan for.


my concerns this year now are the heat, I’ve got my hoophouse over winter doing perfectly with the things that need to be above frost/freeze over winter but it gets up to 110F in summer here- I’ll probably pull all the siding off and throw shade cloth just to keep things from burning.

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I used a 30 inch ABS culvert to line a dug well which was about 15 feet deep. Very strong but light enough for two people to carry it to the site. I had to buy a 20 foot length, so I used the leftover section laid horizontally at the bottom to act as a reservoir for water (the aquifer would slow down filling quite a bit as the summer wore on). The pipe is large enough that I can hang a ladder inside the well to do plumbing. Because of the deep ribs in the pipe I can also climb out if I need to. A little bit of peace of mind for any claustrophobia.

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