Your instincts are correct - it is difficult for smaller plants to survive in the shade and dry soil under any evergreen and the acid soil in your area makes it even more difficult for flowering plants. I suggest more adaptable groundcover plants that also bloom. Try ajuga, vinca minor and lamiums for evergreen foliage as well as spring blooms. If you take the time to add plenty of organic matter (this holds moisture) and fertilize each spring with a slow release plant food like Osmocote you may als0 be able to grow saxifrage, brunnera and hosta. If you really want annual flowers with lots of color than place large pots under the tree and grow shade tolerant lobelia, begonia and impatiens in containers so they won't have to compete with the tree roots. Thanks for reading the column and Keep Growing, Marianne Binetti