Underground Tree greenhouse

Hello has anyone had any success with doing tropical trees for subzero climates? I am in northern BC and would like to do some year round tropicals thinking about digging 10 feet into the ground and then using a standard green house on top?
http://www.treehugger.com/green-architecture/build-underground-greenhouse-garden-year-round.html
Unless theres althready a thread like this please link me!

Go to the greenhouse forum and search around for "walipini" threads. I think you'll find that's what you're looking for.

I recall reading something about Nebraskan farmer who grows citrus trees; quick web search came beck with this.

Jason Silberschneider wrote:Go to the greenhouse forum and search around for "walipini" threads. I think you'll find that's what you're looking for.

At that latitude? Nah, Walipini's going to be shaded all winter.

An Oehler style underground greenhouse [on a south facing slope or at least bermed up on the north side] is the answer here. Probably going to require a certain amount of supplemental heat, but that can be optimized.

David, I hope to have success with tropicals in a somewhat frigid climate in the next year or two. I've done some research on my own but I'm nowhere near fully informed. That being said, some things I'd think about are:

- 10' into the ground is great but you need decent light to get to the plants. If you're on a South facing slope that will help. If the glazing diffuses the light that will help. If the trees are tall enough to get to the light that will help. But all of that may not help enough for you to have trees on the South side of the greenhouse. Plus your morning and afternoon sun would be blocked as well for a while. Imagine taking the roof off of your house and then think about how much light would get over the 8' walls and hit the floor in late December. I'm guessing a lot of your house's flooring would be shadowed all day.

- The portion of your foundation/wall that is above the frost line will be very cold. Warmer than your exterior temps but still below freezing. So you'll probably want to insulate on the outside of your foundation.

- Tropicals need to be above 40F and they prefer to be 60+. So the ground heat will help keep their roots in the 50s and will help keep the air warm. But you will certainly need some supplemental heat to get the greenhouse air warm enough.

- Your glazing will be the biggest heat loss. Insulating the North roof and having the best glazing on the rest of it will help. Some folks have used blankets strung across guy wires at night to keep heat from escaping. That requires twice daily maintenance though.

- I think bigger is better. The temperature fluctuations will be reduced if you have more area under roof.

- Don't forget about having enough vents and cooling options for the summer when it's awfully sunny.

These are just some ideas, I wish you the best of luck!

I will be implementing a RMH into the ground to keep the roots warm. Perhaps I can setup some rails on the north side and have a pulley system to pull a reflective blanket up at night and down in the day time to maximise sunlight. For the actual above ground level I could just have two french door sliders on each side to get venting it needed. The area I am planning on doing this is in merritt BC which is semi-arid climate.
Thanks for the tips!

Would the RMH be the primary heat for the greenhouse? I am imagining that the roots would be tolerably warm enough if they're in soil that is that deep in the ground. But every extra bit will certainly help.

One thing I heard with curtains is that you need to have a decent seal around the perimeter to keep warm greenhouse air from circulating to the cold side of the curtain. You can accidentally create a cooling air circulation pattern that defeats your intended purpose.

I looked up Merritt, BC and it looks to be fairly close to the southern end of BC. If I have the right "Merritt" then the sun angle won't be nearly as bad in the dead of winter as if you were in northern BC. I'm at 45 degrees in northern Wisconsin, the Merritt I looked up was at 50 degrees. Lovely Fort Nelson is at 58.5 degrees. If I'm doing the math right, my winter solstice sun angle is about 26 degrees and yours would be 21 degrees. Fort Nelson would be 12.5 degrees.

I hope your greenhouse works out. How big will it be? How tall can the trees get before they hit the roof? When will you build it? I'm selfishly hoping to learn from your efforts

My plan is for a 19' by 40' gothic greenhouse that is at grade with the long dimension running E/W. I'll insulate the North half of the roof to R20 and use double greenhouse film and a blower on the South half. I'll insulate down 2' and out 2' to combat the 4' frost depth here. I'm not sure if I want to dig the growing floor down very deep because I hit pure sand after 18". I could dig out the topsoil and set it aside, remove some sand and then put the good stuff back on top. I'm also hoping to avoid a foundation wall and trying to come up with an expandable design in case I want to make it longer in the future. So digging may or may not work with that. But it would give more room for trees. I hope for bananas, citrus, avocado, mango, etc. A little jungle to hide in during the cold of winter.

I will have a few hundred acres to play with so if this works out I have no problems greenhousing a whole damned acre at a time if needed.
My main concern would be tree roots. I would like to use a wicking bed style setup maybe without a liner and just compacted rammed earth, similar to the way they sepp holzer does his liner free ponds.
The problem will be deciding how to run the water vs the heat. With the tubes laid down for watering I think they will work better on the perimeter while the RMH heat tubing would be run through the middle.
Will the tree roots go toward the water or toward the heat when it gets cold will be the question and I wonder for exposure for whatever comfrey or nitrogen feeding of the trees... if i would be better off making the floor a \_/ shape maybe a 10-20 degree slope rather than flat.
The Depth I will go will depend on which trees for which green house, but I have no problems renting a excavator for a month and making a few different height troughs.
This will more likely be for next summer before I break ground tho, want to do the best research possible

Sorry for my lack of RMH knowledge, but how does it heat the ground? Do you heat water and circulate it or would the exhaust pipes go through the ground? I think your bigger heat issue is keeping the air in the greenhouse warm enough. My guess is that if you develop enough heat to keep the air above 50F, the ground would be at least 50 since the earth below should be 50-55F. But maybe I'm all wet and don't understand tropical tree roots or the subsurface ground temps in BC

I haven't worried about watering with my design. I've been planning on putting in a sand point well and pumping water or filling a water tank to water with.

Are you going to be there EVERY day in the winter to tend to the RMH and curtains and other critical heat infrastructure? If not, you may want to think about if you can automate them. I contacted a tropical greenhouse person in the Rockies and they started with a RMH and gave up on it due to the frequent fires they had to maintain.

I'll have to do some research on wicking beds, I'm currently uninformed on the subject...

I can use either method so far i'm leaning against using water because of what i've seen from tree roots going inside and breaking plumbing pipes over time. I believe it's the water that attracts the roots not the heat hopefully....
This is just tree roots in general nothing to do with tropical. There is the possibility of using wood pellets to automate the RMH.
Wicking beds are just one of the components of an aquaponics system which is also interesting but I dont like tilapia
The weak link of an aquaponics system is running out of food to feed the fish however with healthy soils/compost there should be no shortage of worms.
Unless I find some way to dig and capture worms however it could be too time consuming but I know it will be a possibility with technology in the future.

If you're just circulating heating water in a closed loop (PEX, solid irrigation line) the roots shouldn't be able to get into it at all. I think they just get into pipes that have holes in them (drip lines, sewer lines with bad joints, leach field pipes, etc). If you're heating with exhaust, I wonder what the temperature trend will be as you get farther from the heater. Will it be too hot for the first 10' and then good for the next 40' and then too cool for the last 40'? I guess it depends how big an area you plan to heat.

I like the wood pellet automation idea. And if you have circulating water lines for heat, your "going back to the drawing board" option if you get sick of the RMH could be to put in a pellet boiler to just heat the water.

I know nothing about aquaponics and I don't like tilapia either so you're on your own for that

I'd be tempted to design in lots of thermal mass in the form of water and then add fish later if everything is working out. But maybe I'm too tentative...