Marginal pond plants are the biggest group of plants by far. Marginal plants are also available in both hardy and tropical water varieties. Marginal plants and submerged grasses are used to add dimension and give your water feature a more natural look. They help "soften" up the udge of the pond where the border transitions into your landscape (mulch, beds, stone etc...) A majority of these plants will thrive while kept in 2-6 inches of water. They are also one of the best natural filters for the pond because of the large root systems they produce.