Thinking as a landscaper, my first suggestion would be to change your choice of plants.

How many nights a year are you going to have to heat the wall? What are the record cold temps in your area - you have to build for the maximum.

You need something to hold the heat next to the plant, or else you will be trying to heat the whole back yard and your heating bills would be horrendous.

That means building a greenhouse sort of structure that covers the wall and plant. It might be easier to make a temporary greenhouse with a frost-cloth cover and lean it on the plant for the expected cold snaps. A 60-watt bulb at the base or a string of tiny Christmas lights is all you need to keep these things warmish.

Hi, lazygardens:

Thanks for the time to put some thought into this. It has me somewhat stumped, but I know there's a sensible way to do it.

The plant I'm growing is relatively cold-tolerant, and can handle temps down to 20 degrees with little problem.

I happen to be in Maryland, in the suburbs of D.C. (don't hold that against me); we're zone 7 here, so our lowest Winter temps CAN range from 0 to 10 degrees F, although I must say that with climate change we don't have many winter days in that range these days.

Our really cold winter weather comes in December, January, and February. If my heated wall were on a thermostat, I wold guess that it would go below 20 degrees F possibly 10 to 12 days a month for those 3 months. So I'm really only talking about 30-45 days where the wall would require heating, when the temperature dropped below 20 degrees.

I realize that it sounds like I'm trying to heat the great outdoors, but the vine will be ON the wall, and it is my contention that a heated wall will keep it alive if it falls below 20 degrees.

As far as covering with any sort of plastic or greenhouse type material, this is not tenable, because the plant will be dormant, and any daytime temps above 40-45 degrees or so will cause it to break dormancy. Then a cold(er) spell will kill the new growth achieved by breaking dormancy, and cause a greater problem which may kill the plant.

What do you think about mounting spot or flood lights on the ground in front of the 6-foot wall, and placing them on a thermostat so that they will shine on the wall when the temps fall below 20 degrees F? Of course these lights will have to be covered or protected in some way so snow or freezing rain does not ruin them.

I took your idea of a string of lights along the wall a step further, because I would have to cover the whole wall to protect the string of lights from breaking if any moisture fell on them and froze.

This proves that two heads are better than one. I would not have thought of the flood/spot lights if you did not suggest the string of lights.

Do you know of any particular flood lights intended to give off heat, or are they basically the same (depending on equal wattage?) I know I can't use a heat lamp, as they consume beaucoups electricity.

Thanks for the thoughts. It is a help.

I am not sure there is a way to do what you are trying to do.

However:

Paint to wall black to absorb solar heat in the day time will help.

Have some kind of hooks and when the temperature prediction is going to be low, throw a tarp over the whole thing.

dcarch

What type of vine? Reason I ask is normally you would protect the root ball during the winter....not the vine on the wall.

That aside heating 180 cubic feet of mass 20 degrees above zero is going to take a lot of heat. Lights and paint aren't gonna do it unless you can significantly heat it during the day so it can release the heat back at night. Even then, the wall is going to lose heat from all sides and may actually work against you.

Maybe..a big maybe, you could bury some thin wall (goofy) pipe with heat tape inside it, close to the roots of the plant. Cover the ground (around the roots) with about 12" of straw. It will probably survive.

Just a thought....

I protect the roots with thick mulch, and they're deep enough that they won't die 'til the temps are below zero. It's the above ground vine that can't tolerate the cold and will die back to its roots. Wall is already painted a dark color to absorb daytime heat.

Just wondered how they're building cement slabs these days with heat inside--either electric or piped hot water, I guess--heated floors, in a nutshell. Trying to take that same principle of a horizontal floor with heat and go vertical with it--as in my vertical wall.

So trying to stand up a heated horizontal cement slab and have it go vertical to be my heated vertical wall. Seems so simple if I could understand and duplicate the "heating" mechanism inside the slab.

If the wall is part of your house, and you don't insulate it to the MAX, and assuming you heat your house... that may be your best bet.

Stringing 'christmas' lights along the vine and turning them on at night will also help. As this must be a deciduous vine you can cover it with burlap instead, but not both - fire hazard.

Which direction will this wall face? If it will be generally south-facing and in the path of prevailing winds, it will absorb and then radiate back the sun's heat as well as protecting the vine from the harshest winds.

A stone wall or bed can usually create a micro-climate raising the growing zone by one half to a full zone.

Is this the type of vine that will cling to the wall or a trellis, or is it something you could lower to the ground each winter and cover with mulch or some other protective covering?

Christmas lights can be surprisingly effective in providing just that extra bit of warmth. Just be sure to use exterior grade lights!

A frost-protection weight floating row cover might be better for your vine than a tarp or sheet of plastic. It admits sunlight and "breathes", but does help retain the heat and impedes the wind (and attendant dessication).

One Christmas light is about 7 watts. = 7 x 3.4 BTU = 27 BTUs.

IMHO, There is no way it can keep anything warm in an outside environment with a little wind going.

An electric heater will give you 5,000 BTUs, even that is not enough.

dcarch