I'd reccomend something airy to contrast with the iris leaves...... maybe linum lewessi ...... lychnis blooms alot although its not lacy..... amm majus is nice though annual..... loves cool summers..... cerastium might be nice around the border...... also likes cool summers.... silver foliage and white flowers..... some of the coreopsises have beautiful airy foliage...... I don't know how they feel about cool sunners....... I don't know much about hardpan so don't know how russian sage would do there since I think it likes well drained soil..... but russian sage is drought tolerant and pretty...... blooms in fall... might look nice behind the irises...... sort of lacy foliage...... :)

Thanks flowerandthings, These are great suggestions. I had to look them all up because I am still learning names. I 'm thinking the lychnis and cerastium would look great-- and I see them planted around here a good bit, so they should do well. And russian sage behind--that would be fabulous. I'm surprised I don't see more of that here. (I see it in the nursery, but not in peoples yards.)

Thanks!

My Russian sage got much larger than I thought it would. It grew into a large shrub.

I just planted moonbean coreopsis with my iris. I think they'll look great together with moonbeam's pale yellow flowers and finely cut foliage. I've linked a pic below but you can't see the foliage, unfortunately. I think it's a nice contrast with the sharp iris leaves. Moonbeam has a long bloom time too.

Another plant that I've been using a lot and really love is rue. It's a herb with beautiful silvery blue foliage. The yellow flowers are insignifcant by comparison. The plant looks good all summer and will reseed but not overwhelm.

Here is a link that might be useful: Moonbeam coreopsis

I use Artimisia powis castle with my iris. It has a silvery green foliage that is lacy and grows fairly low. The powis castle has a wonderful clean fragrance when you brush it. It is also drought tolerant.