I saw Ian (Desert Northwest) at the NHS sale today, he confirmed that he supplied the plants for the new zoo exhibit. Anyone interested in hardy exotics should go have a look. Other parts of the zoo also have neat plantings, I especially like the extensive outdoor jungle effects around the rainforest and tropical animals.

Guilty as charged. I haven't actually seen the planting since it was installed. Thanks for trying to make it sound exciting. I'll be thrilled if any of those Trichocereus spp. make it through the winter. I think T. pasacana might have what it takes to grow here in the right spot... but a northeast facing slope isn't ideal.

Spaced out tombstone planting looking artificial at the moment but some roughness will develop over time. And desert plants are often spaced out like that in nature, pale mulch and heat coming from pavement in front may warm things up for them enough for it to work. Being in shade during sharp frost might assist hardiness, as it does with broad-leaved evergreen shrubs - unless the situation with succulents is different.

I think it's just the opposite with succulents. I guess we'll find out!

A guy in the English midlands has a Trichocereus pasacana in his garden; it survived 12F last winter without injury.