weeds/grass among flowers
You did not mention the weeds that you are trying to control and there is no magic bullet.
In ornamental beds among the iris you will have to hand pull or use a weeding tool. Or you can carefully paint glyphosate , a non selective, weed killer on the foliage of the weeds that you are trying to control. You will have to protect all desirable plants.
Some pre emergents such as Preen, active ingredient, trifluralin control grassy weeds and some broadleaf weeds. This product does not kill existing weeds.
You would have to read the label for the weeds that you are trying to control and follow label directions.