Last night I attended a talk about the native bees of the Bay Area and garden flowers that will attract them. The program was one of the San Francisco Natural History Series that take place once a month at the Randall Museum in San Francisco. (It's at www.randallmuseum.org, click on classes, lectures, and Natural History series, but the site is not up to date, so you may want to call for info.) The speaker was supposed to be Gordon Frankie, who is studying native bees at U.C. Berkeley, but he sent a graduate student in his stead, and I am afraid I have forgotten her name.
However I didn't forget what she said about bees and garden flowers. More than once I have had a discussion of this matter and ended up, with others, wondering whether the flowers that attract these pollinators were only California natives, or if they include other flowers. This talk had the answers. So far, they have found that many non-native flowers attract one or more of the approximately 300 species of bees found in the Bay Area, and that many natives do as well. You can see a list at http://nature.berkeley.edu/urbanbeegardens/ as well as a wealth of information on the bees and ways to make their life easier so they can thrive and help domestic bees pollinate our crops.
So what is the photo? This is an Eryngium, or sea holly, in bloom I know, it looks unnatural. But this is the right color, vibrant blue flower heads, bracts, and stems. It is a non-native garden flower, a perennial, that attracts many kinds of bees, from tiny ones to larger. Surprisingly, Eryngium is in the same plant family as celery and carrot, though it isn't edible. It is a sturdy, moderately drought tolerant flower that doesn't require rich soil, making it ideal for Bay Area gardens.
Besides eryngium and cosmos, other common nonnative attractants are Gaillardia, Bidens, Rudbeckia, Echinacea, sunflowers, and all sorts of mint family herbs like sage and rosemary. Among natives, there are coyote brush, ceanothus, several native buckwheats, California poppy, gumplant, and matilija poppy.
A final tip is that you should try to leave at least half of your soil unmulched, since most of these bees are solitary, putting their eggs with a store of pollen underground. (They are not aggressive, since they don't have a group nest to defend.) They can't dig under organic mulch, and can't get through plastic mulch either.
I have seen some of the bees shown on the website, and look forward to seeing more. Has anyone else watched a leafcutter bee cover her underground nest with the circle of leaf she has removed from a rose? It is a nest roof!