Cats can be very independent and roam free where they choose. Unfortunately, whether it's your cat or a neighbor's, they sometimes may roam into your own flower beds. If these flower beds are toxic, that can be a real problem if the cat tries to eat it. Certain methods to deter cats for going into flower beds may work for some and not others, so experiment with a couple and see what works for you.
Mix up your own repellent by combining two parts of cayenne pepper, five parts flour and three parts dry mustard. Keep in mind that for a flower bed that is 7 by 7 feet, use about 1 pound of flour. After mixing it together, sprinkle it around the flower bed area and within the bed as well. You want enough to provide a generous layer of it in and around the flower bed, so that you can see the fine dusting.
Crush up eggshells or pine cones and sprinkle them around the flower bed. The unpleasant texture these will create under the cats' paws will deter it from walking around in the bed. You will need enough so that they create a fine layer wherever you want to prevent cats from walking, so this could take a large amount of egg shells or pine cones. For example, if you have a garden bed that is 5 by 5 feet and you want to keep cats away, you will probably need at least 15 eggs to get enough eggshells.
Place dishes of sliced lemon around the flower bed. Some cats can't stand the smell of fresh citrus, and won't enter an area that smells like it.
Use a commercial product called Shake Away that is scented with the urine of predators to cats, such as coyotes and bobcats. With this product, you sprinkle it (it can come in spray or powder form) around your flower bed's borders, as well as within the flower bed. It will not alter your flowers. You may want to even apply it within a few feet outside of the flower bed borders so cats stay far away.