What is the earliest species of solidago to bloom in central Maryland? Also, has the botannic name changed for some or all solidagos?
The online publication, "Native Plants for Wildlife Habitation and Conservation Landscaping", which has photos and cultural information, lists 10 native species in Maryland and the Chesapeake Bay Watershed. Of those, the zig-zag, early and dwarf golderods can bloom as early as June. Much would determine the bloom, however, depending upon a plant's immediate situation or micro-climate.
We highly recommend the publication above as a reference for Marylanders. There is more information and many great photos at the Maryland biodiversity website, where you can use the search box for goldenrods.