I was recently looking through plant lists and lamenting all of the great trees that won't survive in my USDA zone. :_(
Being an engineer, I came up with a little idea for a planter which should allow the growing of less hardy warmer-climate trees and shrubs in a colder climate.
Specifically, this design focuses on:
A) Multiplying the solar gains through collection angle/surface area
B) Concentrating heat near the trunk and root stock
C) Retaining heat for overnight storage
A) Does not account for frost damage to leaves, blossoms, or fruit, except through heat transfer within the tree.
(Which may or may not be adequate.)
B) Does not address potential damage caused by snow/ice on accumulation on the leaves.
Anyway, the construction diagram is shown below. The labeled components are:
1) Raised, insulated container back-filled on the North* side. This could be as simple as a straw-covered mound.
2) Heat-retaining wall (optional) on North* side.
3) Sealed reservoir acts as heat exchange for roots and also as overnight heat storage.
4) Thick insulating, yet water-permeable, layer such as straw.
5) Thermal siphon loop of tubing wrapped to trunk with insulating layer.
6) Since planter is both small and raised above grade, heavy, cold air flows around.
7) Passive solarwater heater panel on South* side and angled toward winter sun.
* Assuming Northern hemisphere. If Southern hemi, reverse this.
I hope it stirs up some ideas and helps someone expand their options!
I'm told that the first step is to admit that you have a problem, so that's good ;)
I really like what you've come up with and I'd very much like to see you prototype it. I think that it has a good chance of working, but I'm not a tree-guy.
I don't want to be negative at all, but I've done a fair bit of product development over the years and I can't help but look at ideas without considering where something would fit in the marketplace. If it works, I think your market would be people who'd like to grow only a few trees, maybe with the ability to expand. I'm sure there are markets I haven't thought of, and you could probably make a nice business out of it.
I could be totally wrong, but I think your market would be limited to small-scale applications, which may still make for a viable product and market. My feeling is that, if you want more than a few trees, it's probably a better bet to put in a greenhouse, especially one with thermal storage, like the guy in Nebraska who grows oranges. That may be a much smaller market than the market for your solution; I didn't look at what's out there at all. The greenhouse is proven technology to some degree and it will take time to build up a track record and a history of success, but it's doable, for sure.
One of the things I hate most about the net is how many people shit on others who want to do something. If people are already doing it, you'll hear a lot about how unbelievably hard it is to do and, if it's something new, you'll hear how it'll never work. It's no different than talking to people in person about stuff, it's just that the internet lets everybody on that forum take a whack at you. So please don't take my words as anything other than stuff to think about as you pursue this. Permies is a great site to get constructive ideas from and it seems to be a hotbed of entrepreneurship with many different products getting developed by people here.
A piece of land is worth as much as the person farming it.
-Le Livre du Colon, 1902
The concept is good, and for marginal-but-almost-hardy trees I think it will help a lot and open possibilities for regular good fruit rather than occaisonal fruit. One observation I have made might help. I can grow bananas here, but they are very marginal. Banana plants are essentially a rhizome with an aerial pseudostem, so I wanted to see if warming the rhizome would help the fruit quality. I heated the soil to different degrees, mild soil heating helped a lot, but as the differential increased the growth results became dramatic. At 20C soil temperature in mid winter (when soil would be around 10C normally) the banana plants collapsed dramatically on one cold night (air temp around 4C), but at a temperature where unheated bananas alongside suffered no damage at all. It looked like the plants had been hit with a flame thrower. What I take from this is that in an extreme cold event if the plant is 'unnaturally' kept in active growth when it would normally be (semi-)dormant the damage will likely be significantly increased.
A few questions / comments.
Does the container have to be closed on the bottom? I would think you would want to connect back to the ambient earth and maybe insulate down the sides a bit to reduce lost heat. Also i prefer to have natural drainage / somewhere for the roots to go...trees tend to have large root systems. Are you saying that the raised / insulated container could be straw or that the back filled north side would be straw?
I really like the idea of the passive solar water heater panel providing additional solar gain and radiating into the area to create micro-climate...I think that would work wonderfully. I worry about the trunk being wrapped with a heat exchanger. For a single tree where someone has a lot of time to mess with it, I don't see a problem, however I worry about it being left on too late and damaging the trunk of the tree (just like all those "trunk protectors"). Honestly I think if you kept the heat under the mulch and prevented the roots from freezing that you could easily extend your USDA Hardiness zone by 1-2 zones.
Instead of wrapping the trunk, your north wall (insulated) that is heat retaining is going to provide enough microclimate to protect the top of the tree. It's not like your putting a banana in Montana (or at least i hope that's not the plan).
Also how does one allow for natural break down of materials on top of your sealed water reservoir? Or does that have to be removed from the system every year...since it is making things warmer stuff will break down on it and you want that stuff in your soil.
My opinion of some modifications:
1. Don't elevate the structure as much
2. Heat wall becomes required (redirects the cold around the tree, reflects heat into the micro climate)
3. Use pipes in the ground that can stay there forever...compost goes on top and moves around your pipes. (reservoir is created via lots of bends and turns)
4. Insulate down and away from your tree (into the ground)
5. Keep the passive solar panel system.
That's my two cents...and they probably aren't worth two cents...so maybe that's my cent and a half. Anyways great idea...really like the creativity and it's something I've been pondering about for some time so thanks for sparking my imagination.
Also an engineer and don't have very much experience with trees, but here is my 2 cents!
I would think that if you could use varieties that lend themselves to espalier -controlled growth, such as against walls or fences- you could drastically reduce wind-chill and better fit the trees to your designs. If you knew a bad storm was coming, it would make covering the tree with a concrete blanket or such very easy.
Are you thinking fruit or nut trees or trees for aesthetics? I think the biggest trick would be finding just the right amount of help to give because trees have some capacity to adapt to their environment.
Run a search on fruit walls on this forum. One of the topics will be be about fruit walls and urban gardening in the 1600's. Click on the link provided in one of the replies. According to the article I'd say they did a lot with much less engineering and expense. If the walls worked for them I'd think your idea would pamper the trees much more.