One of my favorite hard surfaced look is flagstone softened by groundcover planted joints. Growing is the easy part as thyme, lysamachea and even Irish moss are hardy enough and spread quickly enough to survive, thrive and achieve the desired look within two or three years. The problem I have run into however is keeping undulated flagstones clean from soil runoff and puddling during heavy rain or spray washing.

Does anyone have any experience with a flag stone jointing solution for this. My build technique is to construct on a 0-3/4" base and set the flagstone in stonedust then return and hollow out the joints to 4" or so, top up with soil and plant. Even if I leave soil and planting level below top of stone I still run into a messy problem in certain areas.

Thanks for any advice.