Terracotta pots will dry out faster because they are porous, but that's all.

Therefore i suppose plastic pots "retain" moisture better

well I would say terracotta because they actually retain a certain amount of moisture within the pot itself and, because they tend to keep the compost cooler, there's less evaporation.
On the other hand, a terracotta pot that has warmed up will retain heat longer.
Plastic pots also tend to have far more drainage holes, across the whole of the base, while clay pots tend to only have one hole.

On the whole though it is the compost that determines the moisture retention as far as your plants are concerned. Fill a plastic pot with claggy clay and it will hold water; fill a terracotta pot with sand and water will drain away.

I'd go with terracotta or glazed clay over plastic for appearance and stability.

Terracotta lose more water than plastic pots because they're porous, as Badfish says. Which is one of the reasons why they've usually only got one hole in the base - the water evaporates from the walls of the pot as well.

That is so useful and fascinating - many thanks Badfish, Urbanite and Bamboo for your insights.

My OH is adamant that my young trees (I grow bonsai) should be in terracotta, whereas I've kept them in plastic until they are ready for a proper bonsai pot . . . whichever they are in, I water them copiously. I now have 4 baby Jacaranda trees, so 2 will go in plastic and 2 in terracotta and we'll see how they compare!

Thank you very much :))

Ah well, most bonsai pots are glazed on the outside, meaning they're shiny - if they're glazed, then they don't evaporate water from the surface of the pot - its no longer porous because of the high shine glaze.

By the way, 'argument' and 'discussion' are synonymous with each other - on the other hand, where strong feelings are displayed, 'row' and 'quarrel' and 'ruck' might cover a disagreement;-)))

I think Bonsai are grown in terracotta as a mature tree purely for tradition and aesthetics....there wasn't plastic pots hundreds of years ago and with Bonsai, the pot can be almost as important as the tree.

I grew many many trees for Bonsai, usually all in plastic, but their final pot was always ceramic or terracotta (both glazed and unglazed are used)

Do terracotta pots retain water better if they are glazed? Also isn't air as important as water for the roots?

Yes, Bathgate, glazed terracotta pots do retain more moisture than unglazed ones and, again yes, air is just as impotant as water. Plastic pots do not need watering as often but can easily be overwatered with the compost becoming waterlogged, much to the plants detriment. We keep all our flowering sized plants in unglazed terracotta and just use plastic for propagation purposes.

I may have confused you a bit . . . my MATURE bonsai are all in glazed terracotta pots, but the 'baby' ones are the ones I was asking about . . . so I'm more or less doing what Badfish did.

The roots are in very gritty compost Bathgate, which helps.

My indoor pots are all glazed terracotta but that's just for artistic expression and to match the decor.

The answer has been given - bonsai has been around for hundreds of years - plastic has been around for tens of years. If you want to carry out a traditional 'art' then use traditional materials.

The same chemistry that makes clay pots porous so that some people think they dry out, means that they also absorb water. It is the compost that matters NOT the pot when questioning water retention.

Blimey Urbanite, keep yer 'air on. We already know you don't agree with what's been said, difference of opinion duly noted!

Bad day at the coal face!

Hope its a better day today, its hard to remain equable on difficult days, as I know from personal experience;-)

"All's Well That Ends Well" and thanks for everyone's contributions :)

No students around today, head of dept said we could go home at 3:30, England having another great day against the Aussies and I've just been sitting next to Ashley Giles one of my cricket heroes.
And it's the weekend!

And the U.S. Women's World Cup champions were saluted with a ticker tape parade in New York City.

☺☺