Flagstone Pathways

Has anyone had success planting between flagstones? The pathway we had laid around the gazebo looks OK but I would really love to have some low growing, creeping plants as shown in this landscaping book. These appear to be creeping thymes which will take foot traffic. Yesterday I dug holes, added good potting soil, and sprinkled with expensive, organic, thyme seeds. My fingers are crossed. I feel this is a leap of faith. Will the squirrels dig up the dirt from above, or the chipmunks and voles from below? Will the rains come and wash it all away before the teeny tiny seeds have a chance to grow a root, a stem, a little leaf?

If the thyme grows I may try other low creeping plants and would love lavender and chamomile along the inside edges, perhaps some Irish moss - want the area to look more like a "Secret Garden", a little overgrown and faded by time. Actually some of the flagstones have already started turning a bit green where they remain damp - these pics were taken late last Summer when all was new and perfect!