Which perennial plants could be grown in a container of only 2.5 inches depth?

I'd think of something along the lines of the alpines, those succulents (hens and chicks?) would be ideal. Herbs - maybe thyme?

Why not look at the Campanula family, they are sooooo pretty. Slow growing, which will be fine in a pot, and has really pretty trailing stems. Don't forget to add stones at the bottom of the pot for drainage! Lindsey

Cooking Thyme.. Lemon Thyme and Thymus herba barona (Carroway Thyme) which grows flat on the ground has purple flowers and lovely scented foliage.. as Madmum says Sempervivums, Sedums ( The hardy Succulents ) are ideally suited , Pennyroyal and Calamint are the two other possible small herbs with scent. You wont have room for all that lot!

use it as a viola pan. these are often scented and being smaller than pansies are really pretty.

Ooops, sorry! I've had a quick look at the campanula's to see if I can give you the right name, but all I can find are the tall varieties, sorry!!! But still don't forget to put stones at the bottom of the bowl, it sounds lovely!

I would suggest sedums, sempervivums and saxifrages although all are low growing plants.

Bonsai trees don't need much depth of soil. A bit pricey though.

Remember that the c ompost in a shallow pan has very little capacity to store water so the pan will need regular watering or should be used for plants that don't need much.