The frog and I eyeball each other for a bit, then I catch a newt wiggling its arse at me, annoyed perhaps that I have woken it up. I know they’re here only because I have parted the waterweed to see what’s going on. I need to rescue the waterlilies from a forest of floating waterweed, but it’s a happy place if these two are present.
Oxygen equals life, and life in the right balance means a low-maintenance pond. Too little oxygen results in a stagnant puddle. One way of adding oxygen is a pump, but life is short and oil is scarce, even if we can’t quite believe it.
The other choice is to use plants. Waterlilies release oxygen through their roots into the pond’s soil. Submerged plants, aka oxygenators, float just below the surface and usually only their flowers emerge above the water. They also help to keep the water clear of algae and provide wildlife with shelter.
The classic examples are spiked milfoil (Myriophyllum spicatum), which turns a lovely bronze colour as summer progresses. Whorled milfoil (M. verticillatum) has more fern-like foliage but is equally delightful. Or our native hornwort (Ceratophyllum demersum) floats in summer and sinks in winter, where it takes root, thus doing a good job in both places.
Water solider (Stratiotes aloides) is a lovely addition if you have space. Each plant spans around 20cm and looks like a pineapple head. Like hornwort, it floats around during summer and sinks in winter. In a smaller pond marestail (Hippuris vulgaris) is ideal as it prefers shallow water, tolerates shade and is evergreen. The leaves are edible, too.
Another good one for spawning wildlife, particularly newts, is willow moss (Fontinalis antipyretica). It needs to be sited at the edge of the pond, but will grow down into deep water. It won’t do well in a pond clogged with blanket weed, which will easily swamp it.
The leaves of common waterwort (Callitriche palustris) hold fish spawn well. It is a delicate thing with tiny star-shaped leaves that form mats across the surface of the pond. It is not a floater and needs to be planted up in an aquatic basket and dropped into a deeper part of the pond. It needs at least 20cm of water above and can take much deeper water. It is an effective oxygenator, but also provides cover for wildlife. If the weather is hot it will die back, but reappear when the water cools again. Water violet (Hottonia palustris) has primula-like violet-coloured flowers that are held above the water in spring.
For oxygenators to work, there has to be the right number of plants. Those that want to be anchored in soil should be planted no more than 90cm deep in sun or part-shade. Floaters choose their own home, but if you are buying 9cm pots or bunches of floaters, aim for two plants for every square metre.
