Plants that like poor dry earth like Rose campion come to mind. How much sun is there? Lavender and Rosemary do fine if in sun.

Heathers would like the ericaceous soil and would be OK until the conifers are big enough to make the ground too dry.

Are we talking dwarf conifers? yes agree with Steragram a tapestry of spring/winter flowering heathers would suffice.

Hi, i cant remember the variety now, ones variegated green and yellow, all three are about fifteen feet now. Gets sun in the morning but quite shady most of the time

15ft is not dwarf and there does not seem to be many dwarf conifers as those with 1960's rockeries and 30ft trees will attest.

True - for Dwarf read Slow Growing! Anyway heathers would still be OK. Perhaps azaleas would be worth a try with plenty of acidic mulch. Or lots of rockery plants would tolerate dry conditions and be cheerful.

I didnt say they were dwarf? Thanks for the suggestions

Depends on the care you are willing to spend under or around trees; if they are the main event (as they are in one of mine), you probably will want color? Azaleas for spring, foxgloves, anemones for the fall, and of course, ferns. I have found that the roots do suck up quite a bit of the water so you really do need to mulch everywhere.