Please see following post for correction. This correction states the entire root of the dandelion must be pulled to prevent it from resprouting.
A special idea, Mark. Not unlike your wheelbarrow trough ;) How does it look like now btw?
Good color on the "semps" in spring, but the whole affair got weedy during summer, I tried to pull some weeds here and there, but many of the weeds are taprooted dandelions that seeded between the semp rosettes... I plan to extricate the perennial weeds in spring. The area my wheelbarrow planting was also ignored, as was my main Allium garden... this year with this new & crazy job, I had so little time in the garden that parts of the garden became disastrously weedy.
A small paintbrush used to carefully apply roundup to the leaves of weeds is helpful. In a tight spot, like your semps, I would use a razor blade to cut the taproot below the crown. Generally, I believe prevention is the best medicine. I put weed fabric down under my mulch and only cut holes in it where I actually plant. This works well for perennials and shrubs. The easiest way to weed bulbs is to let them go completely dormant then spray the weeds. This worked well until I decide I needed something to cover the bare ground. Snapdragons have seeded into the area where I grow Spring bulbs and now fullfill that need.