This question was just raised on the houseplants forum (click on me to see it) where I think I argued convincingly in favor of terra cotta over plastic and other impermeable materials that allowed no increase in gas exchange at the root zone:

I really like gas permeable terra cotta containers and choose them most of the time for anything I'm growing on & don't really need to have in an especially attractive container - though I do enjoy the look of a nicely patinized clay pot. Terra cotta is especially good in situations where the soil is not drying quickly enough, because it allows water vapor transfer through the container walls & bottom. It can, in some cases, allow you to use a soil that you could never use in a glazed or plastic container and maintain optimum vitality; and even if you are using a soil that allows fundamentally sound irrigation practices, I still feel you'd be pressed hard to so readily find containers made of a material less expensive and/or more conducive to good plant vitality.
Just don't let them freeze.

I thought I was careful enough to be sure it was clear that I was commenting on the benefits of terra cotta from a physiological perspective and the materials affect on plant vitality, but I think that point went largely unnoticed, as every poster that preferred other materials to terra cotta mounted their arguments from a grower's convenience perspective.

In many cases, the good of the plant and grower convenience are mutually exclusive. That a container made of other material might be lighter and easier to move, or that it may extend intervals between waterings, that they may be more durable, or that "plastic works best for me" are all things that speak to the convenience of the grower and not to a more vital plant.

Terra cotta is an excellent choice and perhaps the best one we have readily available to us (durable fiber pots are at least their equal, but suffer in the longevity dept in comparison) when we consider its use strictly from its comparative benefits to o/a plant vitality.

Al

Al, I think you explained it perfectly ... the physiological perspective of plant growth vs the convenience perspective of some gardeners. Thank you so much for your comments and the link to that thread.
Now, I'm off to buy another "real" terra-cotta container.

Randy

How about concrete pots? Do they have any advantages/disadvantages. Do they ever leach any lime? Filix.

Mhhhh ..... advantages or disadvantages, eh? Well, one advantage is that that they are very stable in windy conditions. The bad news is they are so heavy you'd think they were made of cement.

Concrete is less porous than terra cotta, and in most cases is so impermeable we should say there is none of the additional gas exchange terra cotta provides. Also, it does initially leach lots of lime. You can stabilize that tendency it to the point where you can use them w/o much concern by plugging the drain & filling repeatedly with a mix of vinegar and water to neutralize the basic (as in opposite of acidic) nature of the material - or, you can leave them outdoors over the winter, exposed to the elements, which will do the same thing.

I hope that Randy doesn't mind if I tell a little semi-related story here. I frequently wander through the dollar store or places like Big Lots, looking for containers for the plants I propagate & give as gifts to friends & garden visitors. I got soooo excited one day when I was at Big Lots and found serving bowl sets that were beautifully drip-glazed and had a crackle finish. I immediately envisioned beautiful dish gardens in them and bought all they had. They came in sets, but were sold individually. The sizes were approximately 3-1/2 gallon, 2-1/2 gallon, and 1-1/2 gallon and were priced reasonably at $6.99, 4.99, and 3.99, respectively. I think I bought 3 full sets & three containers that were from broken sets. Since they were serving bowls, I set up a table & drilled drainage holes in all of them on a Sat.

Our bonsai club buys assorted dwarf conifers and assorted evergreen & deciduous dwarfs from Iseli Nursery in Oregon. I think we pay about $5 each for them and usually sell them at art fairs, etc., as a fund raiser. Well, I bought a whole assortment of 20 and thought I'd sell them in the bowls as dish gardens, so I planted them up in bonsai soil.

Now, I rarely have trouble keeping plants alive, but every one of the plants were dead within 2 months of planting. Soon after I planted them, I noticed a white residue on the surface that was weeping through from the inside. It gradually got worse as the plants died, until the point where I emptied the bowls of plants & soil. Under the pots, I found gobs of a white reside, so I applied a little vinegar to see how basic it was - it was extremely caustic and was obviously the cause of the plant's demise.

I was actually quite astounded, as these were SERVING bowls & meant to be used for that purpose or for decoration. I have no idea what was in the clay it was made from, but my guess is that there's a good chance it wouldn't benefit anyone to consume it incidentally via food served from them!

They were made in China, btw. I threw them all away, along with the dozen or so plants that died in them - an expensive misfortune. ;o)

Al

Hope it's fine to revive an older post, but I was interested and shocked by Al's experience with those bowl/pots from China.

Kinda scary, if you think about just how many "cheap" and discount ceramic planters out there. They're on pallettes at costcos and ace hardwares and long's drugs for great discount pricing, and I always wonder if there's lead or other heavy metals either in the clay or glaze that might leach into the plants.

I have little kids at home and we've tossed many many toys this last year because of the whole lead exposure issue(s). When I started buying pots this spring for all my citrus and blueberries, I've deliberately steered clear of the "Made in China" label because I have NO idea what they're using and I'm afraid of metals or other chemicals leaching into the food. Call me crazy, but I'm erring on the side of caution.

Anyway, relative to the original post, FWIW I prefer the rich and architectural look of terra cotta and I think they hold up better in the long run. So I was glad to learn that they're also preferable from a plant physiology standpoint... I'll be sure to use that one the next time I beg the hubs for, yes, a-n-o-t-h-e-r terra cotta pot. :-)

And another side note... it used to be there was the "Made in Italy" terra cotta (which I love but they're expensive) and the "Made in China" options at Home Depot. This last time I went to HD, almost all the unglazed terra cotta at my local store is stamped with bit "Made in USA" so I think that the market is responding.

I also noticed that the large plastic planters at my local Orchard Supply store (formally sourced in China) are now stamped "Made in USA"... who knew we even had plastic extruding/manufacturing plants left any more in the USA. Interesting trend.