Hornwort This submerged aquatic perennial is an invaluable oxygenator. Ceratophyllum demersum is capable of growing at great depth which makes it particularly useful for oxygenating deep ponds and lakes. The long stems of feathery foliage float freely in the water unless anchored with weights to keep it in the desired location. Commonly known as Hornwort, a British native perennial that has the ability to take up nutrients quickly, making it an excellent competitor with algae. Allow Ceratophyllum demersum to grow until you have 30% of your pond volume filled then remove some by hand - take out the yellow coloured stems in summer months, it will sink to the bottom of the pond during the winter months. Sold by the bunch. Position: Full sun to part shadePlanting depth: In water from 30cm (12’’) to 350cm (11.5ft)Growth rate: SlowFlowering Period: May to JulyHardiness: Hardy