Obvious con is cost. Big time. That's a huge amount of mass to heat. But I like the idea!

Have you thought about the more passive alternatives? If the wall were in full sun then that in itself would help alot. I had a house, brick on the back and part of it had a slate patio--all full sun. A rosemary plant put right next to the slate patio and brick wall is still alive today--5 feet high! Perhaps you can have microclimates within your courtyard where the heat coming off the wall from being in the sun all day raises it a zone.

Take a look at the R factor for cinderblock. Pretty sad and non-heat retentive. If it were stuccoed and then painted dark brown or black...then it might hold slight heat better.
Water filled massive drums are the one way in our part of the world to retain heat without paying a fortune for the generation of the heat. Just let the sun do it. Adobe bricks are another absorbtive scheme, but they cost.
I'll never forget taking down the very small porch here that surrounded the old cistern, and smelling something 'different' and fourth course down, we found one of the biggest black snakes I've ever seen, coiled up in the voids in several cinderblocks. It knew a protected place with a southern exposure for its hibernation (but not cooking.)

Sounds like a neat idea.
Maybe you could do some sort of solar power heated panels.

Filling the cores with sand would increase the thermal mass and extend the solar heat longer into the night. Concrete cores in 12" block would be better. Even so, I'm not sure there would be much heat left by dawn. Painting the outside of the wall white or pastel would create a slight insulating effect (reducing radiant heat loss). Painting the inside face a dark color would increase solar collection a lot but also make a very hot area in summer. Probably none of this would be significant except on the wall that faces south (north end of enclosure).

The electric heat would be prohibitively expensive-- you'd be trying to heat Virginia.

I don't know how expensive it would be. We have pipe wrapes around our pipes in a crawl space. Just enough so the pipes don't freeze and I didn't notice a big jump in our electric bill. But I think some kind of solar powered heating system would be the way to go.

A solar powered system isn't cheap either- but I do think they are otherwise a great way to go. I think a darker shade brick, coupled with southern exposure, coupled with some sort of method like a wire cage filled with leaves (or some type of covering like a cold frame with row covers) would give your zone level a boost without having to put in the heat. I don't know how much radiant heat the wall would give off with the cables. I think if you priced it out, you might as well make a greenhouse, and have tropicals all winter.

I am the last person to coach against it being a sinner many times for out of zoning it in my rose growing ... but if I recall correctly, the south wall is how the Brits fake it as warmer. You may already have a partial zone when it's built.

But if you want to pursue and want ideas try looking whether they have "vertical" pumped hot water heating of a wall - becoming more common as in-floor heating for new houses in Alberta. Hot water passes through loops of plastic pipe embedded in concrete and covered with tiles / rug. Just don't get a hole in the pipe when driving your climber supports in.

There was a great old BBC series I once watched called the Victorian Garden (or Gardener) and it touched on the benefits of "The Wall" in vegetable gardening. The wall was not really for looks or rose growing but privacy, and to deter precocious pleb poaching by my ancestors or was it wildlife control with a zone busting benefit.

The British "warm wall" is partly the consequence of uninsulated stone and brick dwellings that are transmitting heat out of the interior-- insofar as there is heat in the interior ;) A south-facing retaining wall would be second best because of the enormous thermal mass behind it.

Why not a living wall with a tall hedge? Tall overhanging branches trap a lot of warmth (if there is any to trap). Of course I'm in wimpy Zone 9b, where the lowest we see is the mid-teens. We have evergreen (not coniferous) trees and shrubs that can do a lot of the work of protection for tender plants in the garden.

Presumably this wall is oriented to the north of your rose garden?

Thanks for so many ideas and comments. I really like the idea of solar panels. I wonder if I could get them installed on top of my barn. More to think about.

Robert

Robert,
Solar panels to cover a barn would be a tad expensive.
But, if you were to use that expanse to heat water and ciruculate it, you might heat your house's hot water usage and then recirculate it through the garden.
We've been watching solar panels for quite a while and the prices haven't dropped significantly.
If you can do your own plumbing, and have a well (that gets the water temps up into the 50s even in winter), then further heating on a south facing roof....
Ann

I've read about solar-powered pool heaters. Maybe something like that could be used.
I think you mentioned you are a science teacher, why don't you get your kids to draw up ideas for you for extra credit. It could be fun to see what they come up with.

The pool heater idea might be a viable one. I do know those are out there. Still very expensive at 3K or so. There are cheaper models that pump the water through a black set of pipes that heat up in the sun. probably way cheaper. If you spend 15-20K, you can get a system that will put money back into the grid. Not really cost effective unless you are there a long time, but a great way to get off the coal fired grid of your area.

I believe there are 19th c. examples of brick heated walls in rich "country gentleman's" gardens. Unfortunately, I can't give you a reference. Don't recall the technology, but do recall that cost was not an issue.
Hmm, that's probably not helpful.
Speaking of hot walls, I've a brick wall and had 2 roses planted on the south side of it. They died -- think it warmed up too much during the winter, made them think it was spring, then ha ha -- cold again!? I'm replanting, but worried they'll die again come winter.

Would glass blocks be too ugly? Or too glare reflective causing an annoyance? You could intermingle them with some other construction material.

Also filling clear bottles with water and let the sun heat them, I know, I have some wacky ideas.

Why not just build a greenhouse-type wall? You could use old windows.

I finally dug up on goggle the correct title on the BBC series (3 of them). The one I saw was called the Victorian Kitchen Garden with a synopsis of:

"Behind the red bricked walls of Chilton Foliat a traditional kitchen garden is restored."

That would be interesting to see again as I remember it being a walled in garden - they did it similir to a Year at Kew (each month of the year). The gentleman in charge of transferring the knowledge of how it was done was a second or third generation PG as opposed to PE or aka "professional" head gardener. Amazon.com for 50 pounds sterling

England was full of walled gardens, usually brick. Remember the story, "Secret Garden"? I always loved that.

I think probably except in extreme conditions, just a brick wall could push your zone one notch, and that could be the reason they built them in England, and bricks were probably cheap and plentiful there.

What did you decide to do? I'm interested in passive solar heating but do not have the mind for the technical aspects of it.

I notice that when my hose sits in the sun, I have to run it out so I won't be watering my plants with water that might be too hot, even on a day like today which was chilly but sunny.

What could one do with 100 old hoses?

I think I still might try running a heating wire through the wall (or at least a part of it)...I'm really only trying to protect a few more tender roses/climbers through the very coldest part of winter (maybe 3-4 weeks).

Although the ideas of water bottles and old windows would probably help, I am trying to get a an asthetically pleasing look.

Running the water pipes through the wall seems way too complicated for me...and potentially problematic...especially if the power were to go out (which it has done) and the the pipes should freeze and burst... I don't want to have to have a back up generator for a couple of Marechal Niels and maybe a bougainvillea...

Regarding the 100 old hoses? I would think they would fit in nicely at the dump. When I bought this property over 10 years ago, I found the remnants of old fences in which the previous (and only other) owner of the property had incorporated old rubber hoses into the fencing...it looked like a trash dump...

Robert

I agree about the aesthetics totally. My musings always lead to nothing, there is always something wrong with everything I come up with. I came up with some of my schemes thinking about winter survivalism if the power went out for a prolonged period, line the sunroom with bottles of water (too heavy and would take too many probably wouldn't work anyway), decaying compost/manure generates a lot of heat (also can start a fire), etc., considered other options along those lines that don't depend on fossil fuels. Even corn burners need electricity for part of their cycle for auto loading and forcing the air through the heat ducts. Price of corn is expected to be much higher this year.

I wouldn't want my yard to look junky either unless something would work and I could hide it. That's the only reason I brought it up. I am both surprised and annoyed by how much hot water one hose can store, it wouldn't heat up enough in colder weather anyway.

Wires are probably your best option. People around here who have the latest use them in their driveways and sidewalks to melt the snow and ice.

If it's only a month each winter, why not try shade cloth? I'd experiment this winter before doing a large scale implementation.

I have shade cloth over an arbor. It provided enough winter protection to save tender perennials near it from freezing during our weeks in the teens. In fact, I could see on a single plant the effect of the shade cloth. It was like a shed cover: the part of the plant not covered froze and died, the part nearest the shade cloth survived.

We've mentioned R values, thermal masses as heat reservoirs and there is one mention of plants.
FWIW, of the areas in my garden in the recent freeze unpleasantness, the least damage was where the plants were massive and fully leafed out.
I don't know if it was the increased evapotranspiration or just so many leaves diffusing the cold wind, but even the weeds growing in among the massive roses did better.

Where I'm going with this is a test...I've had Susan Louise out on her own, covered with a box/trash can/whatever just to try to keep her alive. I'm not sure I shouldn't try to grow another one INSIDE of one of my massive HMusks and another inside of R. bracteata...just to see if plant mass has protective capabilities.

Carry on.