Mason bees prefer reeds over cardboard tubes or wood nesting blocks. The slight variation in size between individual reeds allows the female to pick a size of her choice, and it also encourages other native pollinators to nest.
Our natural Phragmite reeds are hand harvested, and cut to 6" length which is an optimal nesting length for mason bees. The reed hole sizes are about 8mm and approximately 6" long. At the back of the reed is a natural node that seals the reed and so prevents parasitic wasp access.