Great way to kill grass in your flowerbeds is to keep your soil moist. If you aren’t keeping your soil moist, you’ll eventually end up with a very dry soil. This can lead to many problems with your flowerbeds. One of the most common issues that occurs when your soil is too dry is that it will start to break down. This means that it will start to become acidic. When your soil becomes too acidic, it can be harmful to your plants. One of the easiest ways to keep your soil moist is to add a layer of mulch.