# Pit Greenhouse anyone?



## adamtheha (Mar 14, 2007)

I live in Southern Alberta, zone 3(b) and our growing season is about 3 months, if all goes well, of course. I've been looking at greenhousing to not only extend the season, but make some money as well, and I think that pit greenhouses hold the title for most efficient in a cold climate.
Does anyone here use a pit greenhouse in a cold climate? I don't mean a two foot hole, I mean an honest to god 5-6 foot pit with a cover, even if it's a small one.
I'm just wondering how cold it can get outside before the inside of the pit would freeze. It can get down to -30 C/F (same thing) here, but it usually doesn't get much colder than -15 in March, and warmer from there. I'd probably take a winter vacation in Jan/Feb from gardening.

My thoughts are this: multiple long trenches, about 7 feet deep and 12-15 feet wide, maybe 50 feet long, giving me around 500 sqft of growing space per pit (You can't grow in the shadow part). If I could extend the season to 7, 8 months, I could more than double my production per area, and get better prices for out of season food.

Google "Walipini" for more information, apparently they are doing this very sucessfully in Bolivia, but I don't know what Bolivia's climate is.
I'm actually really excited, this sounds like an awesome way to garden!

Side note: I just polished off a PAIL of garden peas, from only about 100 plants, and that was just two days worth of growth!

Anyone try this yet, or know someone doing it?


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## Windy in Kansas (Jun 16, 2002)

http://faqsolarpower.com/home-solar-power/zomeworks-beadwall-styrofoam-between-glass-3694.html

That site may be of benefit for you to read.


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## bluefish (Jan 27, 2006)

I can't help you yet, but I'm in the process of building something like that. Mine will be 12- 15 feet wide and 20 feet long and roughly 8' deep. I did talk to a guy in Bozeman, MT once, just in passing, that had something like this. His was smaller, but he said with triple wall glazing, his was in the mid 30's F while it was -20 F to -30 F outside. If I get mine done by winter, I'll let you know how it goes.


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## HappyFarmer (Jun 17, 2006)

Just posting for comparison info you might find helpful.

Mine is not quite a pit, but the whole back wall & part of the sides is into a hill, concrete mafia blocks all the way around. I do think it helps with the temps quite a bit. It is 15x33, with three 55 gallon water barrels filled with water for heat retention.

Last winter (our first with the greenhouse) the inside temps remained above freezing until the outside temps hit 0 or below. Even so, my broccoli, beets, and celery survived through the winter with no heat. Much wilting but they survived to give me veggies in Feb/March.

HF


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## pancho (Oct 23, 2006)

What stops the pit greenhouses from becoming a pond greenhouse?


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## adamtheha (Mar 14, 2007)

You have to build this at least 5 feet above the water table, but Southern Alberta is quite dry, so I'm not concerned about high water table. All of the rainwater must be channeled away from the pit, and the cover prevents infiltration from above.

-20, and still roughly above freezing? That's what I like to hear! I bet with a deeper hole, and a proper angle to collect the direct sunlight at the solstice, you could do even better, maybe 45 degrees or so.

If you are thinking of building one, you should see this link:
www.bensoninstitute.org/Publication/Manuals/Walipini.pdf

These guys have got this technology DOWN! I can only think of one thing I'm going to add, a cold sink in the front, where the sunlight doesn't reach. Two layers of railroad ties, backfilled with the topsoil pulled from the site should accomplish that. The cold air should spill down into the trench, be warmed by the earth (at 8 feet down), and rise back up again. We shall see. I am more determined than ever to build a smallish one, especially since I'm already renting a backhoe to bury some water tanks!


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## bluefish (Jan 27, 2006)

You should also read Solar Greenhouses Underground by Daniel Geery. It's by a guy in Utah who built one in the 70's. Was a good read. Lots of technical info and things he did and what he'd do different. Between that and the Walipini paper, you can get some great ideas!


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## ronbre (Apr 26, 2009)

no, my greenhouse got moved last weekend to a spot over the pex from my outdoor wood furnace for "bottom heat"..it is only 4" deep..so it isn't a pit..it has 4" of compost over several feet of gravel that the pex is buried in.

this will be the first year over the pex ..we'll see how it works..but cold air settles..so my concern would be the pit getting too cold???? heat rises..cold settles


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## adamtheha (Mar 14, 2007)

I think as long as you exclude cold air from the outside, the air at the bottom of the pit will stabilize at ground temps.
The most valuable factor in a pit greenhouse is the large amount of thermal mass, also known as the soil. As long as you angle the cover to be perpendicular to the sun at solstice, and stop any heat from escaping, it should stay above freezing. You can also put black colored barrels of water inside to retain more heat, and connect them to the drainage.


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## babysteps (Sep 11, 2005)

Google "laramie, wyoming" pit greenhouse.


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## nataquas (Sep 30, 2010)

adam..... - Digging for my pit greenhouse (20 X 100) should begin next week. The Walipini design first got me interested about a year ago. However well that design may work for the La Paz climate-- http://www.bbc.co.uk/weather/world/...]http://www.sunnyjohn.com/indexpages/shcs.htm
and here:
http://mb-soft.com/public3/globalzc.html
and here:
http://74.125.155.132/scholar?q=cache:vxtOHzlGvboJ:scholar.google.com/&hl=en&as_sdt=400000

Given the La Paz climate, ventilation is probably required daily. Introducing new air on a daily basis should not be a problem there. It will be for me in zone 5a, even more so for you. The often forgotten element in this equation is providing sufficient CO2
for photosynthesis and, it follows, plant growth. The dirt from my pit has to go somewhere. It will make a berm on the north side. Within that berm will be several hundred feet of 4 inch PVC pipe. Air will enter into the piping system at the top of the berm and exit into the pit delivering constant fresh air (and CO2) to the greenhouse.
That idea was a modification of this idea:
http://mb-soft.com/public3/water502.html
(The mb-soft site is brutal to navigate but the guy has some very good ideas)

Finally, the Benson Institute has been mum on the Walipini project since 2002. It would be nice if they would do a follow up. The silence makes me wonder about the success of the project.


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## nataquas (Sep 30, 2010)

Oh, I forgot to mention the walk ways between the raised beds will also act as a cold sink.


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## seagullplayer (Nov 6, 2008)

I saw this yesterday, it might be of interest:

[ame]http://www.youtube.com/watch?v=xfJrbXkWaCk[/ame]

The old tires filled with dirt would help you hold heat.


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## Wintergrower_OH (Sep 21, 2010)

Their is a you tube video on solar pit green house .


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## nataquas (Sep 30, 2010)

Thanx, sea. I hadn't thought of using tires but it makes perfect sense.


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## nataquas (Sep 30, 2010)

winter--I've seen several operations on you tube. Good stuff. Thanx.


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## Wintergrower_OH (Sep 21, 2010)

You will need a "curtain" for night fall to keep the greenhouse warm at night .Walipini design is on youtube . volume is not very good . For the walk way . You will need to have the ground underneath (walkway ) lower than the rest of the green house to take care of the cold air that sinks . i.e walkway platform . Also a way for air to come in and come out. I've seen pictures of use a wind chimney turbine (not sure if this term is correct) . This allow the wind to suck the bad air out . Solar window that open when the heat gets too hot for the plants .


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## Wintergrower_OH (Sep 21, 2010)

This where i got a lot my stuff. 

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm


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## nataquas (Sep 30, 2010)

I've spent countless hours on the builditsolar site.
The 4" pipe in the berm will deliver 52 degree air to the pit year round. Be interesting to see if that will negate the need for the curtain.


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## Wintergrower_OH (Sep 21, 2010)

me too . who want to have to pull a curtain close every night .


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## adamtheha (Mar 14, 2007)

UPDATE
The enormous amount of water that we've had this spring has pretty much melted the walls of my pit...the thing looks like a dirty, nasty swimming pool.
So, change of plans. I'm going to fill in some of the dirt, put some plastic on top, lay some 4 inch drain tubing, and fill another 12 inches of gravel over it. Then, a partially buried greenhouse will emerge from the ashes, like the Phoenix, with the added technology of subterranean heating and cooling. Basically, blowing sun-heated air during the day under the gravel = stored heat. At night, reverse flow = released heat. Plants grown in raised beds, or containers. Very cool! And no groundwater infiltration worries...


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## Paquebot (May 10, 2002)

As you've discovered, they work great as "walk in" rather than "step down". Same principle as digging a root cellar into the side of a hill. Ambient temperature right at the opening ground level but constant earth temperatures the deeper one goes into the hill. Combine that with what is gained by your glass or plastic enclosure and you should be able to gain at least 6 more weeks of growth. Length/size of greenhouse would dictate how many potential 120-day things may be grown while using solar and earth heat. 

Martin


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