I don't know what the official position is but if you don't have a huge amount of them you could probably find someone through freecycle or jumbletown.ie who'd take them (lots of people use them for growing potatoes in).
I had to get a new tyre recently and Kwikfit (or whatever they're called now, the one opposite the Goat near Stillorgan) charge €2 per tyre to cover the cost of proper disposal.