Answer: Crabgrass is really difficult to control in flower beds (as you've discovered). The first plan of attack is to pull the weeds, including the roots; the second is to lay a thick mulch over the bed to prevent sunlight from penetrating (weed barrier or several thicknesses of newspapers plus decorative bark or rock); the third option is to use a herbicide and spot treat the pesky weeds. You can use something like Round-Up near your flowers if you're careful not to allow over-spray to drift onto them. Once you have the weeds out you can use a pre-emergent such as Preen. It is safe to use in flower beds and will stop crabgrass seeds from germinating.
Best wishes with your project!
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