Answer: Pre-emergent herbicides work by emitting a gas that keeps seeds from germinating. This works on all seeds, whether weed or flower. So, put plants in your bed rather than sowing seeds, then use the Weed Prevent. Or, if you're sowing seeds, do not use a pre-emergent herbicide. Any plants that usually self-seed will not produce new plants, because the pre-emergent herbicide will prevent the seeds from germinating.
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