Water plants are essential for a healthy balance in ornamental pools and ponds. Knowing what kind of plants to plant is the key to your success. Some plants should be planted in a pot that can then be submerged under the water, such as Japanese iris. Other plants can be floated on the pool surface, such as the water hyacinth. Other plants, such as bladderwort, are submerged plants that help control the water quality by inhibiting algae growth.