Shasta Daisy plants reseed consistently, and over time, what once was a small crop will turn into a large stand. Over time the stand will become bare in the center, and the side stems will become leggy and fall over. The best way to prevent this from happening is to divide the stand once every three years. You can replant the pieces of the plant in new locations you are basically propagating here. If you prune at this time, confine it to shortening the stems for ease of handling and nothing else.