Ask Mr. Smarty Plants

Yes, that's unfortunately the cycle of life for our lovely annuals: grow, set seed and then die back. Mr Smarty Plants helps this along in his garden a bit by deadheading and generally light cleanup.  Nature has a different approach, the one you indicate.  In the wild, the plants are fully interplanted naturally and in sucession a new flower will arise as the earlier ones are dying back.   What I’ll do in this answer is steer you towards some possible species that bloom later and likely grow higher, while noting that what really cleans up your garden is you in some gardening gloves removing the wilting ones and deadheading those that have finished their glory!

For suggested flowers, we can use the recommended species collection for DC.  I think it’s also fair to check out either the Maryland or the Virginia collections if you like. We can sort these suggested lists for later and/or taller flowers using the sorting capability for size and/or bloom time.

Guessing at your ephemerals:  Camassia scilloides (Atlantic camas) is listed as growing to 1-3’ high and blooming in Mar. to June.  Mertensia virginica (Virginia bluebells) grow to 1-2’ high and are listed to bloom in Mar.-June.

For my example, I narrowed the search in the DC collection for flowers that bloom just a little bit later. I selected "June" bloomers, "1-3" and "3-6" feet tall;  this returned 23 species.  Some attractive flowers from this group include:   Symphoricarpos orbiculatus (Coralberry), Rudbeckia hirta (Black-eyed susan), Oenothera fruticosa (Narrowleaf evening-primrose), Monarda fistulosa (Wild bergamot), Lobelia cardinalis (Cardinal flower), Asclepias incarnata (Swamp milkweed), and Echinacea purpurea (Eastern purple coneflower).  

You can, of course, do your own sort and selection and you should be able to find a nice interplanting that will have a good sucession of flowers into the summer [but you will still need to clean up at some time!]