dilbert, perhaps the styrofoam didn't do it's job? I would think that any kind of banana could survive a cold winter as long as it's kept cool (not frozen) and dry.

Further to gardenguy's post.

In a zone 5, to keep anything cool, not frozen, a heat souce would be required. Styrofoam does not have enough "R" value on its own. Depending on what kind is used, that white stuff has only, maybe an "R 3 to R5" value. So, you'd have to put several layers of it in order to get any real protection.

However, even if it is R 50, without a heat source, the freezing will penetrate. No way around it. But, with a high R value, the heat source could probably be as simple as a 100 watt to 150 watt light bulb or a heating cable, which would be easier to control the heat produced.

And dry sure is the key, as I've been noticing.

Also, to me, logic also dictates that any kind of mulching or protection would have to extend some distance from the stem as cold/freezing can enter from the edges.

When I overwintered my Basjoo, I used 2 old tires stacked on one another, with the stem of the banana wrapped with an old bath towel and some mulch between the towel and the tires. I then covered this all with a blanket and then topped it off with a plastic sheet to keep out the moisture.

If it isn't the insulation it could be the strain of M.sikkimensis. From reports on the UK oasis, and from German growers there seems to be great differences in the hardiess of M.sikkimensis.
It is wideranging in northeastern India, and in surrounding areas at many elevations.
Was yours from a nursery or was it from seed(or both)? Most of the TC'd ones are from Agri-starts, and it would be interesing to find out if the one from there is one of the more hardy ones, but then again in your climate, I'm wondering if any would go toe to toe with basjoo.

Conjecture, shmecture.

Name one person who successfully overwintered any variety Sikkimensis outdoors in zone 5.

Hi dilbert, if you go on this site "hardy palms and more for the northeast" you will see sikkimensis in zone 4 ontario, third year in the ground with pictures. the thread is called "the view from here" by marc. Maybe theres hope for the rest of us.

"Maybe theres hope for the rest of us."

Thank you. He planted next to the south side of his house where it receives heat from the foundation or basement. I don't have that opportunity. The best I can do is plant it next to the south wall of an unheated garage.

I note that his seed came from the same source as mine.

Tropicalvr is right. The species varies alot. Never know what you get from seeds, as they could come from Himalayas or tropics.
From my experience, (comparing to basjoo): Sikkimensis grows faster and larger, especially at lower temperatures than what is normal for bananas. Usually handles a few degrees of frost for a short while, and leaves remain green. For this reason, and since they do not need much heat to start growing, overwintering in coolish, mild areas with occasional frost can be difficult. My basement is too warm (constant 13 degrees C) and the outside is too rainy and wet. Sometimes we also get warm in January (10-15 degrees C), and it may want to grow. Basjoo seems much easier.

Erlend

How fast do they grow from seed... Must you grow it in the ground? You could always bury a big platic tub and remove it late in the year... Maybe i'll try keeping on outside here in WI next winter and see what happens? I think snowcover might also be a big factor. Do you know around the snowbelts of the greatlakes, the ground under the snow doesn't even freeze because the snow insulates so well? Around here we get below 0F with no snowcover!

"How fast do they grow from seed"

Expect it to fill a 4"-6" pot in the first season.

"Must you grow it in the ground?"

Of course, not.

"Must you grow it in the ground? You could always bury a big platic tub and remove it late in the year..."

You can do that with any tropical plant that doesn't require high humidity.

"Maybe i'll try keeping on outside here in WI next winter and see what happens?"

That is what the rest of us are talking about.

"Maybe i'll try keeping on outside here in WI next winter and see what happens? I think snowcover might also be a big factor. Do you know around the snowbelts of the greatlakes, the ground under the snow doesn't even freeze because the snow insulates so well? Around here we get below 0F with no snowcover!"

By any chance, have you ever been to Lac Du Flambeau?