Best flowers for bees?
I suggest you take a look at a relatively new book called The Beekeeper's Bible by Richard Jones. Some of the plants that are mentioned for early spring are malus species (particularly wild crab and pears), clovers, dandelion, hollies (Ilex aquifolium, I. opaca, I. glabra), maples, rosemary, thyme and tupelo (Nyssa sylvatica). Late spring flowering: blueberries, borage, hawthorn, lavender, alfalfa and buckwheat. Late blooming; Fuchsia, goldenrod, heather, ivy and sunflower. Many others are mentioned but these would work in your particular planting zone.
The Beekeeper's Bible is available for borrowing in PHS's McLean Library. Click on link below for details about the book. If you'd like to borrow it, email firstname.lastname@example.org