Mason bees use mud/clay when packing in tubes to build their cocoons and will not nest without a nearby clayey mud source. If your soil not sticking together when squeezed, it is not a good clay source. Adding a clay mix can ensure there is an ideal source of mortar material for your mason bees! You can dig out a hole near your nesting site and add this mix for bees to use when nesting.  Approximately weight ½ lb.