Terracotta isn't as cheap as it once was and adapting flower pots for use as wet pots requires a talent to get
the glueing just right.
However, there may be an option: Italian made terracotta wine cylinders. Some come with a saucer base which will serve as a lid. Unlike flower pots these items turn up frequently in Op Shops so they are worth looking out for. They are deeper than many flower pots and you don';t have to seal any draiinage hole.
I bought one today at St Vinnies for $3.00...
Tip: drink the wine first.
Porous terracotta pots buried under the soil slowly seep out water under the pressure of gravity, keeping the soil moist and providing ongoing local irrigation. These buried terracotta chambers are called Ollas or 'wetpots'.
I've never heard of this, thankyou for posting :) I don't have a garden at the moment but will definitely keep it in mind.