Question is: what can be used to fill bare ground between roses, which later will be covered by rose branches? One that will not interfere with roses' roots.

I tried: wooly thyme, Elfin thyme, dianthus, armeria maritima, arenaria verna, aegopodium podagraria, and (out of line, big, but very early folliage, z2) - oriental poppy. Spring bulbs also, of course, but squirrels deadheaded not only tulips, but daffofils also... Right next to the Fritillaria Imperialis.

Not much success yet with low-growing groungcovers - they grow very-very slowly, thymes have dead bare branches in the center (3rd yr of growing). I was cautioned that watering and fertilizing of the roses could interfere with grouncover development.

Any ideas about grouncover compatible with groundcover roses, that visible already in April-May (days warm, but night temperatures are slightly above freezing)?

Thanks!