The classic plants for very shallow soil in sun are groundcover thymes and sedums. Sempervivums (hens and chicks) would also work. If the area is so small that low growing plants would get lost, then simply replace the surrounding plants with others that would bush out enough to cover the shallow soil areas. Classic bushing out plants include peonies and daylilies.

A 5 ft diameter bed is a very small bed.

What about something that doesn't need to be planted very deeply into the soil? I'm thinking irises?

I was going to say iris too. I have a large boulder by my shed with only a few inches of soil over it and the iris that I planted there several years ago are doing fine.

laceyvail,
The bed is about 20 x 40 feet. The area I was referring to that's 5 feet in diameter is the area with the rock under it that has nothing growing due to shallow soil. All the other perennials are tall , so thought a ground cover wouldn't work well in the midst of that, although sedum might work. Christie and Frizzle - thanks for the Iris idea. I do have some, but didn't think of them for shallow soil. Your boulder by the shed sounds like the same set up. Did you plant the iris directly into the shallow soil? I will pick up some the next time I'm out at the nursery (maybe tomorrow :) ) Any varieties you'd recommend?
Tricia

My iris are just old fashioned varieties that are from my grandmother's yard. I may have done a little soil amending at the time. It's been too many years ago and I don't remember. I don't think they're terribly picky about soil as long as water doesn't pool there. I leave the top of the rhizome showing when planting. You might want to check the iris forum for more info.

Heuchera are a great option for shallow soil.

I'd suggest sedums.

How about monarda? It's shallow rooted.

monarda was going to be my suggestion too. Also pearly everlasting - grows a lot like monarda.

I read an article not long ago where a family brought in some topsoil and mounded it up a bit where boulders met and there was a natural divit leading to a small pocket where bushes could be added. Otherwised they used xeriscape type plants.

High Country Gardens has a lot naturally adept to rocky soil - may give you some more ideas.

I have a natural rock garden on top of boulders, in full sun. The taller perennials that do well are tall sedums (Autumn Joy and some unnamed other), veronica (Goodness Grows), an unnamed geranium, and yarrows. All of these made it through last summer's severe drought, with minimal watering, in spite of the thin soil.

There is an area in the front garden that has a huge stump underneath the soil. It is from a 50 year old Oak tree that the previous owner had cut down and the stump was ground down about 3-4 inches below the surface.

I dug up the area to check out the stump, and it might have as well been a boulder. Oak roots are very hard and take forever to rot. This is the middle of a mixed border with shrubs and mostly tall perennials and annuals. I wasn't going to be able to plant anything like that there, so I spread some aged wood chips and "planted" a bird bath right on top, and made a pathway. It looks nice.

I like the idea of making a nice hardscape feature, or setting up a planter or bird bath, etc. if you end up not being able to grow anything successfully over the boulder.

Thanks everyone for all the great ideas. I'm going to think about the birdbath idea. I have one under the dogwood at the edge of this garden. Maybe I could move it... Will also check High Country for some ideas. Lots of great thoughts. I have several of the plants mentioned, but didn't realize they would work in shallow soil. Maybe some transplanting is also in order.
Tricia