Well it's April 8th and my 3 nesting blocks are up and ready with fresh lined tubes.
I also put up a big can filled with some dried Japanese knotweed reeds i harvested last Fall- those are in all different diameters so it will be interesting to see anyone come to those.

But my cocoons are still in the fridge. Even though we will have more than 3 days in a row this week of over 50F, there is truly almost nothing blooming yet, no willows or maples or dandelions, not my crab apple tree yet...nothing. Even the honeybees are just barely bringing in any pollen, and they forage several miles out, unlike masons. I strongly feel my bees will not find enough in their forage radius to live on yet, so I'm keeping them chilled a while longer. Another good indication to wait is that there is no activity yet at the nesting blocks from any wild neighborhood mason bees, so I don't think any have emerged yet in the wild. Last night was around 25F.

I have about 50 tubes of cocoons, but I figure each tube may only have an average of 3 viable bees emerge successfully. I estimate low.
They are split between eastern blue orchards (Osmia lignaria) and the little brown Osmia taurus, an import from Asia which is now locally abundant.
I also have 10 cocoons of horn-faced bee from Dave at CrownBees.com.
Lastly, there is one lonely filled tube from the 'mystery' bee that got filled in a smaller diameter tube later last summer, and plugged with chewed green stuff- I suspect a leaf cutter bee of some sort. I can't wait to see if that one in particular emerges!

I am using 'emergence boxes' that are the boxes that bank checks arrive in, with a small cut out hole in one end for the bees to get out. I will tie these to the nesting blocks. This is so the bees will emerge and then find the fresh tubes available right there, and not likely be able to find their way back into the check-box to re-nest in the old dirty tubes.

Now I just need to wait for a few trees or flowers to start blooming so I can set the cocoons out...