Last night was the 2nd frost here in as many weeks. I was pleasently surprised after the first one that not only did my mimosas survive, but they didn't even drop they're leaves. In fact that day the leaves opened with frost still on the ground.
Last weeks cold snap was the earliest first frost I can remember.

Our first frost usually occurs in mid December. I debated covering my mimosas, but since they seem to be well established and since I have one growing in my greenhouse I decided to see how they deal with freezing temps. 

So if you want cold hardy mimosas, grow them from seed. What I did was I got 50 seeds, planted them in a peet-pot tray and left them outside, in mid February. After most had sprouted, one night it got down to just below 40 degrees F. The cold killed the little sprouts, but that night six more sprouted in the cold, I gave 3 away and the 3 I have now are the other 3. My trees are well acclimated to my climate since they've lived they're entire lives here, as well as starting they're lives in very cold temps (relatively).

Just thought I should add to our knowledge of growing mimosa tenuiflora.

On a side note, I also have 2 hbwr vines growing in the ground, I cut one down just before the first frost and left the other, the one I cut is already growing back and the other suffered no damage. I also have one heavenly blue who still has a few leaves since he's protected from the north wind, all of my ipomoeas are still blooming, even the ones with fried leaves, and my brugmansia looks as healthy as she did during summer. I built a greenhouse around my largest hbwr and put most of my potted plants in there so they're all fine. I even have 2 heavenly blues that I just started for next year, some tomatoes and bell peppers, a melliton vine and my potted reed canary grass going in the greenhouse.

Beautiful! I've suspected that they can be raised and trained to survive colder climates. Once they're well established and woody like that I'd think they could survive as much as any tree. Mine have been babied indoors but I still have some seeds I could get started in the cold. But it gets much colder here -- that cold snap was 4 inches of snow for me and ground has been frozen for 3 weeks. Thanks for sharing your experience thus far! Looking forward to updates.

very interesting. If you don't mind me asking, what plant hardiness zone do you live in? I would love to give this a try, as I live in a zone 8b/9a area and it doesn't normally freeze over during the winter. Maybe a few small frosts, but nothing too cold.

I'm in zone Zone 9b. I've only seen snow here 3 times in my 35 years. It snows about once per decade. The roads iced once and no one can drive on ice here. Pretty wild. I live on the gulf coast, just south of a large tidally effected lake which keeps my area much warmer than it should be.

I think mimosa can become sufficiently established in one growing season. If one plants enough seeds, surely a few will have the right genetics to survive. I don't see why a cold hardy cultivar couldn't be developed similar to bananas and other tropicals that I see growing further north that where I live.

If the climate scientists are right, the earth can experience abrupt climate shifts, every 100,000 years or so, this means that it's happened several times in the history of the species. Could mimosas native habitat experience freezing conditions during such a period? They grow in Mexico, it gets pretty cold their as it is. So if that's the case, then some seeds have to be able to cope or the species could go extinct. Perhaps?

So Christmas morning there was a fairly heavy frost but my backyard was spared. Leaves only opened half way that day but now they're back to normal still shooting out new growth. We had some rain as well and they've turned a little darker green.

Thanks for the updates and pics BFP. M. hostilis is typically listed as being hardy to zone 9a or b (I forget which), so 8 should be well within reach given an appropriate microclimate. Plus I think you are right on about the plant having enough genetic variability to find some strains that are more cold hardy.

My intuition told me some would def survive. Just looking at all the naturalized and invasive species around here which are native to the amazon, tropical Africa and Asia.

http://is.cbr.tulane.edu/

It seems to me that none of the invasives have much use other than being ornamental. Perhaps mimosa, caapi, acacias could out compete the current pests and also be usefull. Just a thought anyway.
What would be awsome is if caapi vines could out compete the japonese honeysuckle which completely overtakes edge habitats, this spring I'll also be experimenting with growing caapi on Chinese tallow trees. Tallow is out of control and none of the native vines seem to like growing on it.

Okay so tonight it's supposed to get down to around 27 F. I covered one tree but I don't have enough supplies to cover the other one. Let y'all know how it goes.

If you cover a mimosa, make shore you wrap him up tight cause if he can blow around under plastic the thorns will get caught and mangle the branches.

Edit: I found an old think blanket and covered the other tree. Didn't want to take the change and cause the tree to suffer.

Update:

It got very cold (25F) that night from my last post in this thread. That was the coldest I've ever seen here. It was already below 30F when I covered the second tree with 30 mph north winds blowing. I thought they both died, as they're leaves died and were brown by the next day.

Yesterday I noticed that my small tree which I only covered after it had dropped to ~30 has begun to grow again, timed perfectly with my japonese magnolia, I was so happy. It's just one new leaf growing near the base of its trunk but it's alive. I'm attaching a pic. The larger one hasn't showed any signs of life yet but it's trunk still looks to be alive to me.

Hopefully they'll bloom and make some seeds this year, when they do I'll be giving them away on STS so I'll keep you all up to date.