I was in St Paul today and saw Catalpa trees in full bloom. Usually the blooming of Catalpa trees coincide with the start of the nectar flow. Beekeepers should put honey supers on now.
Honey supers go on two at a time. If there is foundation to draw out on new supers they should be place directly above the brood nest.
I use queen excluders under my supers. When I have new foundation in the supers, I hold off on putting on queen excluders until there is new wax and some nectar in the cells of the super. Then I put the queen excluder in.