Answer: Since you're digging the area to remove the weeds anyway, I'd suggest putting down some weed barrier after you've removed the weeds. First, rake out all the red rocks. Then dig or pull the weeds, roots and all. When you've removed the weeds, lay down weed barrier (available in garden centers), or several thicknesses of newspaper. The idea is to cover the bare earth with a light-blocking material. Once you've put down your weed barrier, replace the red rocks. This should keep weeds from popping out in the rock. Sedum Autumn Joy will eventually grow large enough to cover most of the rocks, or you could add a groundcover such as Vinca, Ajuga, Wintercreeper, Cornus canadensis (Bunch Berry), Bergenia, or Lamium maculatum. If you decide to include a groundcover, you'll need simply to push the rocks out of the way and punch a planting hole through the weed barrier, then replace the rocks.
Best wishes with your flower bed!
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