Can I apply composted manure to flower garden in Fall?

Hi- yes, it's fine to apply composted manure in the fall. Pull back any mulch prior to applying so that the compost is in contact with the soil, then rake the mulch back in place. A 1-inch layer of compost should be sufficient. Consider testing your soil this fall if this area has never been tested. You will get baseline information on soil pH, nutrient levels, and organic matter content:
https://extension.umd.edu/hgic/topics/soil-testing

Also, check the nutrient requirements for your perennials as some natives prefer less-fertile soil.
Jon

Great, thank you!