Removal of weeds that have already germinated with herbicides requires a postemergent herbicide. Generally there are limitations to what you can spray and not also kill the plants that you are trying to grow. Here is a factsheet that might help you decide what kinds of herbicides you can add to your toolbox for dealing with weeds.
Postemergent Herbicides for Use in Ornamentals (http://edis.ifas.ufl.edu/wg059) is a 5-page fact sheet and is largely comprised of two tables: Table one lists postemergent herbicides that can be safely used over the top of some ornamentals when used according to label directions; table 2 lists postemergent herbicides that are registered for use around ornamental plants when applied as a directed spray. This factsheet was written by Jeffrey G. Norcini and Chris Marble, and published by the UF Department of Environmental Horticulture, November 2014.