Approximately 30% of native bees nest in cavities. Cavities can include holes in standing dead trees, downed logs or other wood, cavities in rocks and cavities in plant stems.
For the bees that choose to nest in plant stems, they are seeking out stems that are dry/dead and from the previous season. In nature, opportunistic openings in the stems would be made when the winter’s snow load breaks the stems or perhaps from browsing by deer.
Most cavity-nesting bees need an accessible hole or opening in a hollow plant stem.
There are a few bee genera including the small carpenter bee, Ceratina sp., that have strong-enough mandibles designed to chew out the soft, pithy center of a stem if the stem is not hollow.
It’s No Trouble To Leave Some Stubble
One of the easiest ways to provide cavity-nesting sites in plant stems in your landscape is to cut down your perennial stems from the previous season (the following spring), leaving 12 – 18″ of stubble. The new seasonal growth from the perennials will soften the appearance of the stubble and you will be providing many potential nesting sites.
The advantages of this method compared to building elaborate bee hotels or supplemental bee boards is one of hygiene. By mimicking a naturally-occurring phenomena, you are helping to limit the number of bees nesting in close proximity and therefore reducing potential transmission of pathogens or disease.
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