I'm either getting more comfortable with using my greenhouse, stupider, or have the contempt of familiarity - anyway, last winter despite it being really cold, I only ran my heater about 4-5 nights. It is a plastic hoophouse, double layer with air blowing in between. In the sun it will rise 30-40 degrees F' above outdoor actual temps. At night in a short time frame the temp diff is more like 5 degrees F. Still, the most freeze I saw on my pots were a very thin layer on the top that quickly thawed the next day. No problem with new shoots, so even when the interior of the hoophouse was in the teens no problem.

Outdoors, I layed down about 25 pots of Yellow Groove on their sides and covered them with 1 layer of greenhouse, clear plastic. I did this in November and uncovered them in March. To my surprise they were perfectly fine and had initiated new leaf growth. Most, but not all, have put up multiple new shoots larger than the existing culms. These guys had to have frozen to some extent at some point but I think the pots heated up quickly in the daytime and likely did not freeze very deep in the pots. Unintentionally, when I covered them I also covered a couple of small in-ground Heteroclada culms - they were perfectly fine when uncovered but all other culms in the patch are all but top killed, serious culm damage.

I think that it may not take much to protect the pots, out of the wind and if insulated they may be just fine. Surprised to hear that you cold frame did not work well David, do you think voles may have gotten in and feasted?

Exposed pots in zone 6, not likely to do well, I walk past a restaurant everyday that left Yellow Groove in pots out front all winter - the flowers they planted in the same pots look nice next to the totally dead bamboo...

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Brad Salmon, zone 5b/6 Southern Indiana
Winters -20 to -25C. Summers 30 to 35C , humid. 115 cm annual precipitation, frost free from May through early October. 259.3 meters elevation. Growing 150+ species. http://www.needmorebamboo.com/

Brad- I probably did not make myself clear. The plants in the cold frame were fine. It was the unprotected pots beside the cold frame that took the big hit. I think keeping the dry cold wind off, and the daily thaw is all most hardy bamboo need to survive here. I don't heat the cold frame until spring when I start my garden sets, and then not much just several 100w light bulbs.

I might try your idea next year and see how it works here. One difference between our sites could be lack of snow cover here. Just wondering if the plants might overheat at times?

David

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David Arnold
Middle Tennessee Bamboo Farm
USDA zone 6b/7a

Not much snow cover in these parts either and it generally is gone pretty quickly. I thought the heat up on those warmer winter days might cook it as well but no signs last year anyway. One time does not give enough data but I'll try it again. I think I'll also wrap my in-ground Kwangsiensis and some other small guys next year to help them through!

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Brad Salmon, zone 5b/6 Southern Indiana
Winters -20 to -25C. Summers 30 to 35C , humid. 115 cm annual precipitation, frost free from May through early October. 259.3 meters elevation. Growing 150+ species. http://www.needmorebamboo.com/

Live and learn. We will never know new bamboo survival techniques unless we try new ideas. I wonder too if the plastic is increasing the humidity, and decreasing the need for water from the rootball? Were your pots on bare ground or some sort of ground cover?

BTW, what do you think of Kwangsiensis and its potential to live in our hot dry summers?

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David Arnold
Middle Tennessee Bamboo Farm
USDA zone 6b/7a

The pots were laying right on the ground. I 'generally' do not have the dry issues that you do, although the last few years from mid July to early September the rain stops except for gulf hurricanes that drift up. I think we just transitioned out of a long La Nina so I expect this pattern to change this year and to have more regular rainfall here - perhaps you as well. Geez, is that statement the kiss of death or what? Last year I do not recall watering the Kwang although I may have, it was its first year in-ground and I usually water new plantings. It looked fine until top killed last winter, new culms leafed out again and it is perhaps 4-5 feet tall. I think a winter of protection may give it a boost.

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Brad Salmon, zone 5b/6 Southern Indiana
Winters -20 to -25C. Summers 30 to 35C , humid. 115 cm annual precipitation, frost free from May through early October. 259.3 meters elevation. Growing 150+ species. http://www.needmorebamboo.com/

That is a lot more than I expected, but I'm guessing it doesn't work that way on cloudy days. I've also noticed it always takes a few days to freeze a bucket of water placed outside so if there is 8 hours of sunlight on any given winter day, it won't allow enough time to freeze anything in there too badly. The cooling which happens from 5pm until 7am could also be slowed down if the side of the greenhouse is lined up with 5 gallon buckets of water.

I'm planning on getting a cheap green house just enough to fit about 100 plants. I might have to stack the pots on shelves if I can fit everything in 72 square feet.

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http://www.flickr.com/photos/31489820@N02/

http://stevespeonygarden.blogspot.com/

As for potted boos in the ground getting good drainage; my brother has many large potted bamboos buried in the ground. They do a lot better that way, as the rhizomes stay a lot warmer in winter, and they do not get as hot in summer. Dual purpose. He has silty soil, so water does not pool in the pots. They rhizomes also stay put, which is why he does not just plant them. I use wood chips here to stick my potted boos into, so drainage is not an issue. However, the rhizomes are constantly trying to escape out the drain holes. Rhizomes grow pretty much year round when they are warm enough.

Also note that even though a boo may be tolerant of cold weather, that does not mean it will be happier being exposed to it. Compared to say, Douglas fir trees that require cold for setting dormancy. Fargesias here take a beating even at 12-15 degree temps. The only bamboo that I have grown that is truely cold immune in our climate is Phyllostachys nuda. That is seemingly impervious to the cold here. No leaf burn at all. No top damage, no slow-down, first to shoot in spring. Tolerates as cold a temp as any bamboo out there that I am aware of. Read: bullet-proof.

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Happy trails...

It sounds like a full days work to dig enough for over 100 plants, setting up the hoop greenhouse, putting in 10-20 5 gallon buckets of water for temperature regulation, and putting all my solar lights in the greenhouse, but It will be well worth it if all my potted bamboos make it without any cold damage. My 25gal Nuda is definitely going to take some work especially to move it.

I'm estimating on very cold nights even with my waterbuckets, solar lights, extra insulation, ect it will still drop down to 15-20F so I will also keep a thermometer in the greenhouse so I know if I need a heater.

Given plants are in the ground I've figured that moso starts taking leaf damage at 7-8F, nuda at around 5F, rufa(hasn't been tested), vivax 12F, Bissetii(well under 0F), giant rhubarb 25F, mosquito plant 32F, I will turn on some heat with an extension cord to the house. I'm planning on using up every square foot of the green house with potted plants, and might stack them if theres not enough room.

Now that leads me wondering what species will take a winter night in a pot grown inside a greenhouse.

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http://www.flickr.com/photos/31489820@N02/

http://stevespeonygarden.blogspot.com/

sounds like i may need to get started towards a cold frame at least, or if one knows where he wants the plants permanently, I'm guessing it's better to put them in the ground in November (before a freeze) no matter how small the seedling is ... DOES THAT SOUND CORRECT ... or will truly small seedlings / plants benefit from an extra year in the pot with regular watering

I would not plant a small seedling myself. I do not plant gallons, or even 2 gallon bamboos in the ground for that matter. I size them up into at least 3 or 4 gallon pots before they go into the ground here, and more typically 5 gallon. Better survival rates. More for summer water than winter protection. I like to plant bamboos in the fall as well. I get faster growth that way.

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Happy trails...

Thanks for your comments and yes fall has an edge over spring for tree seedlings too according to the forestry folks.

Jeez! All this talk about overwintering potted hardy bamboo has gotten me a little worried. Would someone living in the PNW ~ zone 8 have to worry about some potted phyllostachys sitting on the porch ?

Do your bamboos grow faster when they are filling up their pots as opposed to being planted straight in the ground? I'm guessing since black plastic pots might heat up faster than the ground during the day, or have an extended growing season if put in a greenhouse. On top of my moso and heteroclada seedlings, I have a few potted bamboos too, but haven't had them long enough to observe them.
By the way I'm starting to think a higher soil temperature 65F+ is pretty important as far as the rate of growth because my Dulcis shoot that I'm measuring for growth data puts on more inches on warmer sunnier days, and the same thing applies to leaf output.
I'll have to try using my needle thermometer on a sunny day to see if there is a measurable difference in soil temperature and place the pots in locations it heats up the most, likely on black pavement.

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http://www.flickr.com/photos/31489820@N02/

http://stevespeonygarden.blogspot.com/

I probalby would really reconsider that one.

Hmmmm, I have to add to my last post that growing in pots is not always better for all bamboos. For example, Moso hates being potted up for long, and does not divide down to small one gallon pot sizes very well. It does better in the ground.

You have to avoid cooking boos in pots as well, and growing them on blacktop is probably risky, even in winter. Blacktop will absorb huge amounts of light and radiate huge amounts of heat and do it very rapidly. Black surfaces will also freeze at higher ambient temperatures, like around 35 or so. They give off more heat and will freeze above freezing air temps (black body radiation is weird science). While the radiant heat is good for the area above ground, the pots and thus the rhizomes would be exposed to lower than ambient temperatures. I find that it is better to have gallons of water around my potted plants, and when the temps go below freezing, water has to give off heat energy in order to freeze. I have used old plastic gallon milk jugs filled with water for many years in my greenhouses now.

As for growing/shooting temps, we stalled out here in the PNW again this year, and shotting was late (again). I finally have almost all my boos shooting here after an 80+ degree heat spell during the last 2 weeks. I used to think that bamboo would track with turf grass heat summation for peak fertilizer applications, but I am thinking that bamboo is probably more like 60 degrees than 50. 50 degree heat summation is what is used for turf and pasture management (heat degree days), as well as vineyard management.

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Happy trails...