We intentionally keep a bunch of decaying logs and sticks in our yard for this purpose. I also accidentally left out a 2x4s we pulled out of an old wall (thus

We intentionally keep a bunch of decaying logs and sticks in our yard for this purpose. I also accidentally left out a 2x4s we pulled out of an old wall (thus full of nail holes). Almost every hole, big or small, now has some kind of cap from solitary bees laying their eggs in it.