We always talk about picking the right plants. However, I like Noel's idea about installing some good soil to make a fertile bed for the plants.

Look at the soil surrounding the houses in new home construction projects, it almost always looks like crap in areas with clay subsoils. They either use stockpiled topsoil or truck in topsoil before planting the grass.

Looking at the pictures on the forum, most of the newly built ponds also have low-fertility soils along the littoral area immediately following construction. If you are going to expend a lot of effort to improve the plant population at your pond, I think improving the plant environment is an excellent idea!