We have sago palms near our pool, but it isn't enclosed. Almost every living plant drops something. It's their nature to be reproductive which usually means some kind of seeds. We have society garlic which is very neat and colorful also. You also need to be concerned about roots.

Suzi

Some possibilities are:

Bird of Paradise
Small palm or palm-like plants (such as aforementioned sago; find one that works with the light conditions.)
Croton
Ti
Dwf. oyster (var. or regular ...as a groundcover.)
Various heliconia
Various gingers
Copperleaf

Thanks - these are some good ones to start! :-)

most of those plants are good for no mess, no fuss, but won't handle occasional freezes. Also, expecting plants in pots to handle both drought and torrential rains is not very realistic. You'll have to hand water as necessary. Of the plants listed so far, not all stay below 8 feet tall. If you don't drop much below 29ðF, Phoenix roebelenii, Strelitzia reginae, Chamaerops humilis v. cerifera, Chamaedorea radicalis, Cycas revoluta are all possible choices, not messy, and fairly tough growing plants.