Having grown up in Minnesota, I'm surprised that your bamboo -- any bamboo -- survived one of those winters. Decora is supposed to be hardy only to -5F, so it is relatively hardy among bamboo, but not compared to the temps you would be seeing. I guess it's possible that it's Decora, but Decora is one of the many bamboo that all look pretty similar, so I can't positively identify it from the photos. I'm curious: did you do anything to protect it last winter?

Kudzu - no, but we had a lot of snow - it got down to at least -16 deg. F, but anything under the snow stayed green, which leads me to think that it's not the temp as such, but the desiccating effect of the very dry cold wind that does for more tender plants. I guess the real test will be a really cold winter without much snow. The exposed tops of last year's growth were brown and crunchy by the end of winter. I thought I might spray part of it with Wilt-prufe in the late fall or early winter and see what that does, compared with what had not been sprayed. Judging by the way it came back, though, I don't think I have any worries about the whole thing dying off. I am curious about the ID, though. I hope there is someone out there who might help with that. Thanks for your reply - Tucker.

Tucker,
I'm in Fort Collins, CO zone 5B, but here it is very extraordinarily dry in the winter, with occasional very warm very sunny dry days, followed by bone chilling cold a few days later, frequently alternating warm and cold, but always dry. I planted my decora about 5 or maybe 6 years ago. At the same time I planted yellow groove and ..... hmmmm.... it slips my mind at the moment. Oh yeah, Nuda. 2 years ago, I added Vivax. Of all these, so far, the decora has done by far the best.
By the way, the leaves on decora, do not take on that pretty, shiny, dark green appearance until their 2nd year. The individual leaf, must be in its second year. First year leaves are much lighter in color and the shine of all my other bamboos. It's shoots, just look like shoots to me. Nothin special about them.
Like you, after a couple years, I found that the portions of my decora which were under the snow, or flattened near to the ground and covered with plastic, survived the winter with green leaves and stems, but anything sticking out in the sun became desicated and died. Like you, I suspected that the main issue was not the cold, but instead was the dryness and sun. Each spring for about 4 or 5 years in a row, all mine were dead to the ground, but came up from root. Growth seemed to be maxed out. Then one winter I covered one with plastic and that got flattened by snow down near to the ground, and wow, it made a huge difference in how much growth I got the following spring. I was convinced it must be more the dryness killing the boo, not the cold.
However, last winter changed my mind. My Decora had grown to be a nice patch about 5 feet in diameter, and about 8 foot tall. Last winter I covered the whole thing in plastic and weighted down the plastic on all sides. It kind of looked like a plastic bubble or mushroom or something, about 7 foot tall. Inside of there, the bamboo did great. Occasionally I'd crawl under there and it would be like another little world inside. It was all moist inside and the water would condense on the sides and run down. We'd had a number of days well below zero, and it had no affect on the bamboo inside the plastic. 3rd week of January I went in there and all was well. Then during the last week of January, we had 48 hours in which the temp never got above -10. That did it. Even with all the moisture in there, the decora was trashed. There were a few half alive leaves about half way or 2/3 of the way down afterwards, but for the most part, the boo was dead down to the ground once again.
If we hadn't had those two really frigid days in a row, I'm confident the boo would have made it through the winter completely unscathed. All the moisture in there made no difference. It was the temp that wiped it out. I guess I had earlier just underestimated how much insulating affect the snow has, and how much warmth is coming up from the ground through the snow.

Well, on the sunny side, my yellow groove, which was MUCH smaller, was pretty much squashed down near to the ground under plastic I had also put on it. So, even though its plastic had a couple holes poked into it, the closeness to the ground, or perhaps the proportion of ground to enclosed space, was good enough that it was only modestly affected by those 2 cold days, losing about 25 to 35% of it's leaves. (It was the first time I'd covered it with plastic.) Well, even though it had been much smaller, it shot up about 8 or 9 feet in June. So, now it hasn't filled out as much as the decora, but at present it is just as tall or a bit taller.

I need to find a way to add just a bit of artificial heat under the plastic for my boo on those coldest days. I now know that the varieties I have will do fine down to -5 or even -10 if it's not for very long. They just can't handle extended periods of cold such that inside the plastic the temp really drops down low. Maybe I could just put something like a 40 watt flood light or something in there and just turn it on when I know the temp is expected to drop below zero. Something low power, which would have negligible fire risk, but put out just enough to keep things going.

Bruce

Bruce - Thanks a lot for your reply - not sure what I'm going to do this winter. I may lay the shorter growths down so the snow will cover them, and as I said above, spray the taller ones with Wilt-prufe (sp?). I don't want to go with plastic or adding artificial heat - the goal here is to see to what extent this plant will thrive, more or less on its own, here in MN. Winters here are so unpredictable, both in extremes of temp and snow cover and in seasonal duration of really cold weather, that anything not native is a gamble. Still, I'll probably keep gambling.

Tucker

Tucker - Let me know what happens to the one with Wilt-prufe on it. If that works, it would be a lot easier than my methods.

Bruce

Here are a couple of pictures of my back yard bamboo on March 24, 2012. I sprayed it with Wilt-Pruf about the second week of November, and the leaves were green until some time in February. They have since turned brown, and I'm sure they will all be lost, but the stems are still nice and green, so I have high hopes for their putting out new leaves. The winter was very mild (by Minnesota standards); the lowest temp that I saw here was -12 deg F, and there were not a lot of below 0 days in total. It was, however, very dry, with very little snow cover; actually none for a lot of the winter. This month has been the warmest March on record in the Twin Cities, with a lot of temps in the 70's and even a few into the 80's. Now to watch and wait to see what happens with new leaves & shoots.

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Always fun to experiment!

Tucker