There are thousands of aquatic plant species that live in freshwater. Common types include lilies, floating heart, cattails and arrow leaf. Most aquatic plants are low maintenance once they are planted. Koi may nibble on them or cause some uprooting, but besides that, they need little attention. The most important part of aquatic plant treatment is fertilization.
Use fertilizer specifically designed for aquatic plants. The ratio of nitrogen, phosphorus and potassium should be 10-26-10. Nitrogen encourages foliage growth, phosphorus promotes blooming and potassium is good for overall health.
Fertilize lilies once a month after they are planted in the water. Lilies are heavy feeders. Make sure the fertilizer does not touch the roots or it will burn them.
Handle lotus tubers carefully so you don't break the growing tips. The plant produces tubers instead of bulbs or rhizomes and they require special care.
Push a small hole in the soil around lotus plants during the growing season. Use a stick or gloved finger to make the hole near the outside of the pot. Put two or three pond plant fertilizer tablets in the hole and cover with soil.
Pry apart the roots of some aquatic plants, such as the water hyacinth. This promotes plant growth.