After cleaning your mason bee cocoons, there are a couple options for storage over the winter months. A homemade container is possible, as are commercially produced ones.
Storage Containers
Store the cocoons in a plastic or styrofoam container with air holes for a cold period of 90-150 days in the fridge or in the garage, at 2-4 degrees centigrade with 60% humidity. They need a cold period (colder than 4 degrees C) of at least 30 days to complete their development into adult bees.
Typically the cocoons are supposed to have 60% humidity, which may seem high but it is best not to let them dry out, although they will survive and do fine. Just think of the winter conditions they would be in if they were to be in nature – damp and cold, right?
For moisture, a damp paper towel/cloth/felt pad in the container works well. Or you can use one of those pads that you typically find lining trays of meat that you buy at the supermarket (a friend refers to these as meat diapers) but make sure to use new ones that have not been used for meat. Check regularly for mold on the cocoons, if you get mold, rewash them in the bleach mixture and dry again. Within the container, add a thin layer of water at the bottom, put the paper towel/cloth/pad on top and put your cocoons on top of that.
Storage Locations
You can keep the box of cocoons in the refrigerator or the garage. If you are keeping the cocoons in the garage or shed, put them in their smaller container within a metal container if there is a chance of rodents getting into it. Christmas cookie tins are perfect for this and offer a couple inches on either side for some air movement along with air holes in the lid.
If you plan to store the cocoons in the garage over winter, be sure to put them in the fridge by the end of January and leave them there until you are ready to put them out for emergence. With the warming weather, there is a chance they will emerge too early before there is food available for them.
Spring Emergence
When daytime high temperatures reach 14 degrees Centigrade or more and flowers (a food source) are in bloom within 100m, it’s time to put out your cocoons.
Put the cocoons in a little paper box (small jewellery boxes work well) or an old pill bottle with a pencil sized hole in the side or top. You can create a hole by using a paper hole punch. Tuck the box in the eave of the house and leave it there until all the bees have emerged. Be sure no water enters the box or bottle, as it will inhibit the bees from emerging.
You can tell if they have come out successfully by counting the empty cocoons. Give up to three weeks for their emergence although if conditions are right, they will emerge within a couple of days.
Make sure your bee house is facing east or south east in the garden and is firmly in place, not blowing around in the wind. If the house is facing directly south, ensure it is getting afternoon shade to cool it down as the intense heat can kill or damage the developing larvae.
Out of interest, watch them come back to the nests with their pollen and nectar loads for the nests, these gentle bees will charm you!
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