Rick, I don't think the roots are what needs to be warmer. Once the ground freezes for the winter, it actually stays a pretty constant (and not-super-cold) temperature. The issue is the damage that occurs from the cold winds in winter, which can kill next year's buds. Keep researching, but I think you may find out that a warming cable on the roots will not have the effect you hope for.

Thanks. I know that the temperature stays in the mid-50's below a certain level--maybe 6"down. My thought is that with mulch above, and the cables below, it might be possible to grow certain tropical or tender plants that are typically unable to survive winters in my zone. I'm thinking of bananas first, and then figs. Figs will generally fruit off of new wood, I've had them so damaged that there was not enough biomass left for the plant to fruit, so the idea is to preserve as much of that biomass as possible. As for bananas, these grow from a corm, which can often be rather shallow rooted. If the corm and a good piece of the 'trunk'--it's actually a pseudostem made up of leaf petioles rolled together--it might be possible to grow these in the ground up here. I'm not really interested in the ornamental/winter - hardy varieties like 'basjoo'.

I think here on the coast of CT we're now zone 7a. I guess the best way to answer my question is to indulge my inner Mad Scientist, and plant a banana out there. If I do, I'll post the results here. Nothing ventured, nothing learned! Thanks,

Rick in CT

rredbbeard, did you have any luck? I don't have heat cables but we have an outdoor wood boiler and lines going underground to our house. I noticed that every winter the ground above these was considerably warmer than the surrounding area so we built a raised bed over them. I have managed to grow some plants here in my frozen zone 2 that are zone 4, two zones, for me, is wonderful.

I find that the plant choice must be ones that die back or produce on new wood. I do not mulch ( I tried it and it failed ) as that encourages the plants to begin growth too early in the spring and then when they grow above the mulch the spring weather freezes them off. They do not start much earlier than my other plants but the roots survive in this bed when they would not in our -40 winter weather.

One spring I built a row cover over the bed and it kept it incredibly warm at night. Maybe that would be an option for you?

Hi Ubro,

I experimented a little last fall, planting a fig as deep as I could, which.means 1 foot here. I trimmed the top growth a little. then wrapped the top growth, ~2' wide, in a tarp, which was filled with dry peat moss mixed with crushed red pepper to keep out the vermin thar would like a cozy place with bark to strip. the top of this setup was closed to keep snow and rain from getting in.

After our few snow storms, I shoveled snow on top for added insulation. The mummy was unwrapped about a week ago, and the fig was as good as when it was planted. All the peat was dry, except for a few inches right on the ground.. This past winter was MUCH warmer than last year, going as low as 10°F, whereas the previous year we had 2 consecutive nights of -10°F, and we usually get at least a night or two of -5° to zero°.

I found a source for an inexpensive underground heating cable, so I'll put this underground, and see how a banana does growing above it. I'll report back with any news, good or bad.

--Rick in CT

Such a good idea, I never thought of wrapping with a tarp and filling with peat. I wonder if blueberries would like that treatment? They would at least be a small enough shrub to wrap.

I find it amazing what can survive if covered well in the winter, grapes come to mind. If you don't mind laying them down and piling on the peat some zone 4 ones that fruit early can live up here.

I believe the science when they zone plants, but sometimes you just need to experiment for yourself.

Where's 'up here'?

You might be able to grow your grapes on a trellis that can be detached and laid closer to the ground, but I'm speculating here. Once a grape vine gets established the base may not be flexible enough to take that bending? An alternative might be to espalier it on a south-facing wall, then it might be easier to insulate?

I have all kinds of schemes for experimentation, but if I'm at all successful with figs, I may postpone the banana going outdoors. I'm hoping that if I use warming cables, that the temperature inside any wrapping will be moderated. In the case of bananas, I've considered building a plastic-wrapped frame to fit just the pseudostem to keep it alive.

One suggestion from another banana site is to cut the pseudostem shorter when a bud starts to develop, of course avoiding the bud itself. The overall height of the plant can be substantially reduced without affecting fruit production.

Maybe I have too much time on my hands? <g>

--Rr

up here in zone 2b Canada