A friend first told me about this Boojum Tree (Fouquieria columnaris) in someone’s frontyard in Saratoga, California. I went for a revisit recently and took some pictures of this weirdly wonderful plant. It is native to the Sonoran Desert in Baja California, more than 500 miles to the south of Bay Area.
The success of this specimen seems to indicate that this plant is reasonably hardy, maybe to 25F. The most important aspect of cultivation is preparing a very fast draining soil mix using mostly inorganic material. Our winter and spring rain coupled with cold soil temperature tend to make the roots of succulents rot away very easily. It is not obvious from the photo above, but this whole area is raised by about one foot over the surrounding area. The same idea is helpful for other borderline tropical plants such as Hibiscus rosa-sinensis, except that extra irrigation is needed in summer to compensate for the fast drainage.
There are some other interesting succulents in this garden, including this very blue, very rounded Opuntia and a very nice, vividly marked Agave ferdinandi-regis.