Is this a shady garden - or does it enjoy plenty of sun? If it's on the shadier side you'll have a smaller choice of annuals, unfortunately, though some are very useful (Impatiens, for example).

I've found the following are pretty good at masking the Last of the Bluebells - Hosta, Vinca (perennial), Ajuga, Polygonatum, Cyrtomium, Dicentra, Omphalodes, Heuchera and Tiarella, Lamium, Astrantia, Pulmonaria, Liriope, Arisaema, Fragaria and Duchesnea, Epimedium - and a few thugs of equal vigour, which I won't mention.

For a formal effect - probably the Hosta. The others can be a bit 'cottage-y' in effect.

Good luck with thinning the clumps. :-))

thanks for the suggestions!

Also how long before the foliage withers

Hard to say because of the zone and climate differences. I'd expect them to be withering away by the end of this month.

Mine are dying down now. vetivert8, is using the plants I use in my shade area, the sunny area I have Daylilies, coral bells, and Black Berry Lilies.

In one bed I have the coral bells and fairy rose that seems to be doing a good job of covering the foilage.