The answer to 'why is my flower bed invasive plants' is that your flower bed has become overrun with aggressive, fast-growing plants that are crowding out your desired flowers. Common causes include not properly preparing the bed, planting invasive species, or allowing weeds to take over.
Symptoms of an invasive plant problem include rapid spreading, difficult-to-control growth, and the inability of your desired flowers to thrive. Solutions include carefully removing the invasive plants, amending the soil, and replanting with more appropriate, non-invasive species. For serious infestations, it's best to call in a professional landscaper who can properly diagnose and treat the issue.