lavender? some short version of penstemon? I don't know much either but that has worked for me and the blooming times are right, though lavender's blooming time is shorter. Deadhead the black eyed susan, as it can get out of control reseeding itself :)

Do they have to be perennials????? Of course there's lots of annuals...... purple speedwells..... veronicas....... mallows..... and though they're a little later blooming..... scabiosas and coneflowers...... :) alliums too but they won't bloom through august...... I think short campanulas would work...... :) .... lik creeping bellflower ...... :)

I put in some salvias - don't remember which type - but they are dark blue/purple.

{{gwi:588734}}

oh how pretty!

I grow Bee Balm with mine. It's about 36 inches tall with magenta blooms.