Use the herbicide sethoxydim for effective weed management in flowerbeds, as recommended by the University of Massachusetts Extension. The chemical is sold under different trade names.
A product containing sethoxydim works as a selective, postemergence control of annual and perennial grass weeds. The chemical is sold in the form of emulsifiable concentrate, and is also used indoors. Besides flowerbeds, sethoxydim is used to control weeds in broadleaved vegetables and fruit, as well as in ornamental crops.
Apply the herbicide over the top of the flowers to the target weeds. Use on actively growing weeds and avoid use on drought-stressed weeds. If the weeds are under 6 inches tall, use a lower rate, but use higher rates on taller weeds. Perennial weeds require higher rates of herbicide. Products containing sethoxydim have a low toxicity to birds and wildlife and are non-toxic to bees, as cited by the Cornell Cooperative Extension. Use sethoxydim safely on a number of flowers -- including chrysanthemums, carnations, dahlias, the gladiolus, marigolds, aster, lavender, coleus and zinnia.