Re: Bay Area Garden Tour de Force.
The tree I think is Camphor. He's in Santa Clara here in the bay area..warmest part in summer,and then coldest in winter as he told me its a 9b. Still,with protection of the tree,he's not limited all that much. I saw a Huperzia squarrosa high up,some Flat leafed Rhipsalis houlletiana..so he's keeping most of the deep cold off them.
You can ask him on YouTube about the how does he do it. I like the combos..I had considered Donkey tails Sedum myself. He's able to do that in his backyard. My sunny front yard is not so safe and the tree I have- Ash- is denser shade. But,I still have room.