Grub worms are usually more of an issue in lawns. I have not had any issues with them in flower beds that I have planted. What you are seeing is the immature stage of the the May or June beetles. To confirm whether you need to treat for grubs, examine several soil sections at least 3 to 4 inches across and 4 inches deep (sample sandy soils to greater depths). A good rule of thumb is to examine several soil plugs from widely scattered parts of the bed. Finding more than five white grubs per square foot justifies treatment, although some beds with even higher numbers of grubs may show no damage.

Here's some additional information. https://insects.tamu.edu/extension/publications/html/e211.html 

Thanks for the question