Hornwort

Simply drop weighted bunches into the pond in spring or summer. Hornwort has no roots and floats freely in the water column, absorbing nutrients directly through its foliage. It thrives in still or slow-moving water at almost any depth, from shallow container ponds to deeper garden ponds. Plant roughly five bunches per square metre of pond surface for effective oxygenation and algae suppression. Hornwort tolerates a wide range of water conditions, from full sun to shade, and from acid to alkaline water. It grows vigorously in summer, helping to keep pond water clear by outcompeting blanketweed for dissolved nutrients. In autumn, it sinks to the bottom and produces overwintering buds called turions, which regenerate the following spring. No feeding, soil, or compost is needed.

Thin out excess growth in summer by removing handfuls of the plant from the water. This prevents it from choking the pond. Compost the removed material or add it to the garden as a nutrient-rich green mulch.