<< Will polyurethane finishes/stains work for beehives? >> Polyurethane finishes/stains are fine if you want a nice looking hive. Definitely use spar varnish or some other type of exterior poly. However, the poly will not last and will continually need to be recoated. I use linseed oil as it is easier to put on (lazy me) and also preserves the wood just fine, although it darkens it considerably. I try not to use poly outside because of the maintenance involved.