Hornwort (Ceratophyllum demersum) is a submerged aquatic plant, that grows in still or very slow-moving water in ponds and its slender stems are clothed with whorls of fine, forked leaves that gives an overall feathery appearance to the plant. This plant is a useful oxygenator for your pond. It produces few roots but the stems sometimes root into the mud at the bottom of the pond. Propagation of this plant is very simple, just pull away some stem and let it float in the water. It grows well in water of 60-90 cm deep.
Water hyacinth (Eichhornia crassipes) is a free-floating perennial aquatic plant, with broad, thick, glossy, ovate leaves that float above the water surface. They have freely hanging, purplish black roots and attractive, lavender to pinkish flowers with six petals. As this is an exotic plant you have to lift and overwinter it on trays of moist, soilless compost at minimum temperatures of 13 Celsius degrees (55 F). It can be propagate by runners, stolons, or seeds. The Water hyacinth is a vigorous grower that is able to double its population in two weeks so it can easily become a weed.
Water violet (Hottonia palustris) is a good oxygenating, perennial aquatic plant with long stems that bears deeply divided foliage above and below water and having a spreading habit. In spring are borne stems of pale pinkish-lilac flowers. It prefers still, slightly acidic, shallow water, to 45 cm deep. Plant them in the muddy bottom of the pond. You can propagate it by stem cuttings in spring and summer.
Frogbit (Hydrocharis morsus-ranae) is a fast growing, small, floating plant with kidney-shaped leaves that grow in rosettes on the water surface. It bears small, papery, white flowers with yellow centers that appear in summer. The plants are mostly free-floating, but will root into shallow mud. They sink to overwinter as buds. You can propagate this plant by cutting away plantlets from the parent plant. It needs a water depth up to 30 cm.
Parrot’s feather or Diamond milfoil (Myriophyllum aquaticum) is a perennial freshwater plant that has both submersed and emergent feather-like leaves, which are arranged around the stem in whorls of four to six. Submerged leaves are longer than emergent ones. Tiny, unnoticeable flowers appear in summer. It does well in good light and a slightly alkaline environment. Grow them in baskets of loamy soil in water 15-90 cm deep. It can be propagate by cuttings.
Water lily (Nymphaea Froebelii) is the ideal plant for smaller ponds but their 10-13 cm diameter flowers are still a good choice for any pond. The flowers are pinkish-red with central stamens of orange-red. The leaves are having an attractive bronze color as they unfurl in spring. Plant them in still water with a depth of 15-30 cm. You can propagate them by division of rhizomes in spring, separate offsets or remove plantlets.
Pygmy water lily (Nymphaea Pygmaea Helvola) is a miniature water lily perfect for restricted areas or moderate ponds where only on lily is to be grown. It has attractive, dark-green, rounded leaves, heavily mottled with purple and fragrant, cup-shaped, clear yellow flowers that appear in summer. Plant in depths of 15-23 cm. Propagate them by lifting, dividing and replanting into baskets for aquatics.
Fringed water lily (Nymphoides peltata) is suitable for a wildlife pond. Their leaves resemble small lily pads and grow from long runners, covering quickly the water surface. In summer it bears bright yellow flowers with fringed petals that are held above the water by stout stalks. Grow them in water with a depth of 15-60 cm. Propagation can be done by division in spring or by separating the runners in summer.
Water soldier (Stratiotes aloides) is a free-floating plant with a rosette of spiky, sword-like leaves that are hanging half in and half out of the water. In autumn the rosettes sink to the warmer depths of the pond and they rise again next spring. Sometimes it bears white flowers in summer. Grow them in water with a depth of 30-90 cm. Propagation can be done by separating new plants that form from spreading stems.