The answer to 'why is my flower bed brown patches' is that there are several common causes, including drought, disease, pests, or nutrient deficiencies. Brown patches in a flower bed can be a sign of stress on the plants, which can be caused by a variety of factors. It's important to diagnose the underlying issue to determine the best solution.
If the brown patches are due to drought, the solution may be to increase watering. If it's a disease or pest problem, you may need to treat the affected plants with the appropriate fungicide or insecticide. Nutrient deficiencies can be corrected by applying a balanced fertilizer. In some cases, it may be necessary to replace damaged or dead plants to restore the appearance of the flower bed.