I got a pot of alstroemeria back in 2006, and they've been blooming happily every year in a big fiberglass urn, from November through April. This year I decided that I needed to repot them (and I needed that urn). I've never seen the tubers before -- they're fleshy and come in crowns, like dahlias. They seemed evenly distributed throughout the pot, and didn't seem to be oriented in any particular direction, so I just tossed them back into some nursery pots full of potting mix. If they don't come back next year, I'll just buy some new tubers.