These photos are from a couple of weeks ago. I've been observing the bee oasis and I find that the terra cotta doesn't hold water for very long, which is good for preventing mosquitoes, but demanding for the gardener to keep refilling on sunny days. Maybe glazed terra cotta would be better.
I also used a terra cotta base to hold my mud cake purchased from Brian Campbell (for sale at West Coast Seeds). This is made from muddy clay which you moisten so the mason bees can use it to plug their nests. Less energy spent foraging for clay means more energy for pollinating and laying eggs.
I am happy to say that all the cocoons I bought hatched, and I even held one in my hand while the bee was emerging. It's intelligent eye peering up at me from a hole in the cocoon was very touching. However, the weather has been so cool and wet that I despair as to the fate of those bees and I haven't seen many around since the males hatched. Their doesn't seem to be any activity in my condo.
Meanwhile, in my father-in-law's garden the trillium were blooming and his mason bees were emerging from a neat cocoon container made from a scotch tube. You can see the bee droppings on the outside of the container.
Doug is the perfect person for keeping mason bees being 1) retired, 2) a master gardener and 3) an accomplished woodworker. He started out with rustic homes and has now gone on to make homes with removable tubes. This version is made from hand-rolled paper tubes inserted in foam fitted into a modified scotch canister. (Yes, our family likes double malt.)
They hang on the south face of the garage behind an espaliered fruit tree. It's a shame that his crab apple tree was blooming during that freak hailstorm and the blossoms were shattered.
Here is a wooden home he made with the paper tubes inserted in the holes. I'll have to visit and see if he's got females in his condos.