Mine dont crack because I bring them inside set them on shelves on window sills of garages sheds where ever it can be found in cold storage areas with southern exposed lighting. Think about ground planting your cold hardy cati or hypertufa containers if you lack cold storage space.

No, not only will they likely crack, but you'll also likely lose the plants, too. CHC are cold-hardy when in the ground, not in a pot outside, IME.

I guess it all depends where you live. I keep cold hardy cactus in pots out doors and they are alright but I am 8b. Some pots crack in the coldest of cold fronts. Only one in 10 years. I think it was a very low fired porous earthenware pot. It flaked a bit. I am not in Idaho or Inland BC.

Mara,

8b isn't exactly a concern for most cold-hardy plants, no? I have region envy sometimes.

What I meant about cracking, I meant cracking well...anyway, if a plant here has soil / plant in it and the soil thaws during the day then freezes that night - it's not good for the plant, IME, and the pot might crack, too, especially those recurved-inwardly ones which I now avoid using (they're fun to throw towards the shard pile).

I did not know where Beaniebeagle lived so I thought I would give another thought from a person who lives in the warmer cold effected area. I am not the perfect 9b of Cali and arizona. I am somewhat effected at times by cold. It sure ain't San Diego NOR where you are. I am betwix and between.

beaniebeagle - I have many different terracottas (w/ soil, plants) left outside in winter and they do not crack. But, it hardly rains in Las Vegas and humidity levels usually below 15%, so very little moisture in my pots for freeze-thaw cycle to affect it. And it usually nevers gets below 30F here at night, then temps and sun always comes up during the day. Only occasional days when it may dip down to 20's. However, even if you keep them out of rain/snow, if the humidity is very high, I think the TC pots will still absorb the moisture around it and you can still go through freeze-thaw cycle which may contribute to some cracking.

Any pot that I have had that was terra cotta and outside for the winter has spalled. I've never had one totally crack, though. I think it is the humidity like alex said. Where I am cold hardy things need to be in the ground.

Z4 ,,, SD I bet that ain't San Diego. .......South dakota....BRRRRRRRRRRR

DH got a degree jointly from UCSD and SDSU. We were in San Diego for five years. Here SDSU is totally different university in a very different place. Each place has its charm, though very different.

Mara,

But you're a perfect 8B, surely! I often listen to 'Bewitched, Bothered and Bewildered', usually by Ella, when repotting Gasterias. It also puts me in a betwixt and between space, which helps a lot when you're dealing with northern top dressing.

aseedi,

That's a good way to describe it - rather than crack in cold-but-not-as-cold-as-us weather, it spalls (full disclosure - gears, as in wind turbine generator gearboxes, also spall, but only when they're bad). Calling it flaking is too imprecise.

From Wikipedia -

Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball bearing). Spalling and spallation both describe the process of surface failure in which spall is shed.

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And I love the observation 'Each place has its charm, though very different.' - ain't that the facts! I was in SanD for 20 years until I came to the Southern Interior of BC almost 6 years ago - even in August, you can feel Ol' Man Winter get near.

Mike , my place sits right on the brder of everything. We are on the border of Z8a/8b, the county border and the shop is literally built on a watershed border between to major stream systems. The property is drained by three m stream watersheds. and this ecological zone is the FRACTURE zone of the Edward's Plateau where it drops off into the Blackland Prairie.
And we are not far from the Balcones fault (very inactive) little fault line.

A thicker Terra Clay might have a chance for your zone