New fired pots out of the kiln today
I bought 25 pounds of "earthen-ware" clay (you might see the similarity to Terra-cotta), heres a couple recent pots.
for me the appeal of "earthenware" clay is the texture of the claybody. Earthenware is not vitrified, which means that it has some porosity.
Smaller pots (mame and shohin) especially for non-temperate or tropical trees would probably do just fine. In an environment like a zone 9 and maybe zone 8, I bet it would be fine outside unprotected. Earthenware pots used in northern Alberta's winters (zone 2 or 3) would not be a good choice.
Keep in mind that earthenware/terracotta flowerpots tend to last for a long time. I've seen some clay flowerpots that are 30 years old. In some places in the world, terracotta tiles are used for roofing.
These pots will be fired to bisque temperatures, and then will be "pit fired". A group of potters in my area have dug a large hole in the ground and then add a bunch of fire-wood, and bisque pots. Its an ancient technique.