5 years or so, with varying degrees of success... which is to say, I only have a few right now, and I think they've lost their tags.
the Pacific ones didn't do well for me, most others made it through their first winter. I think Teiderheid is the one in a pot in the rock garden now, and it has survived despite weeds. I'm hoping to provide plants in teh little rock garden "island" with extra attention, but you know what they say about good intentions. I was thinking bigger ones wouldn't get overwhelmed between weeding sessions?