Some questions about plants for your pond

 

Floating-leaved plants shade the pond (in this case, duckweed)

This is an answer to a question from Brian – it turned into a bit of an essay unfortunately.

 

‘I was wondering if you could advise me on your best recommendations for oxygenators and also for surface floaters – i desperately need to add some shade and whilst I will, of course, be introducing some lilies, I am keen to learn about others I can use – water hawthorn seems like a good option but any advice/guidance would be hugely appreciated.’

Hi Brian

A bit of background to the answer first. I’ve written about this a bit on the blog, but putting it briefly, the idea that plants are needed to add oxygen to the water is a bit of a myth. It’s true that plants do add oxygen to the water – while it’s light anyway – but then at night they use it up. Both big plant and microscopic algae do this. What this means is that ponds naturally have fluctuating oxygen levels – and more importantly most things that live in ponds are naturally adapted to this.

Many of the smaller animals, for example, come to the surface to breath air. True pond fish (like tench and crucian carp) often tolerate very low oxygen levels. So do you need to add ‘oxygenators’? Well only to provide habitat.

So what might you add to make good habitat in the water? Some possibles are water-starworts (Callitriche species) which are rooted on the bottom with submerged and floating leaves; Rigid Hornwort (Ceratophyllum demersum) which is a submerged plant that just floats freely in the water – it doesn’t have roots; Curled Pondweed (Potamogeton crispus); the various kinds of water crowfoot (Ranunculus species) and Spiked Water-milfoil (Myriophyllum spicatum) or, if you wnt out into the hills and just looked in some ponds, you could try to find the acid water northern species Alternate-leaved Water-milfoil (Myriophyllum alterniflorum). Other things you could find in the wild are Marestail (Hippuris vulgaris), a whole load of fine-leaved species of Potamogeton (I use the Latin name because the English name ‘pondweeds’ isn’t very helpful).

Best of all, but hardest to find – I’ve never seen them on sale – are the stoneworts, mainly species of Chara and Nitella which are a kind of giant alga which look like ordinary water plants. They only live in the cleanest water – there’s a picture of some we have in a tub at home on the blog at http://thegardenpondblog.org.uk/2008/12/11/whats-in-the-pond-in-december/.

For things with floating leaves apart from lilies, you can grow Broad-leaved Pondweed (Potamogeton natans) or Various-leaved Pondweed (Potamogeton polygonifolius – another you’d probably have to collect from moorland pools); Amphibious bistort (Persicaria amphibia) which has two kinds of leaves – one floating, the other emergent at the pond margin.

Given that shading plants don’t usually cover very large areas of ponds, and fish and other animals survive this happily, I suspect the whole shade thing is also a bit of a myth as well. So I also suspect that in the size of pond you’ve got there’s no real need to have a lot of shade. But these plants are nice anyway, whether they cast shade or not.

The biggest problem is obtaining plants – I’d recommend collecting a small quantity from the wild, with the landowners permission. And remember people like the councils and the Environment Agency often dredge water plants out of rivers and streams, so there’s nothing wrong with you doing a little bit of this too! The plants will grow back. Just stay away from nature reserves because they might have the odd very rare thing that nobody is allowed to pick.

Water Hawthorn – well, you could use it – personally I wouldn’t because its not a native but then I’m allowing my pond to colonise with plants naturally . After 18 months my pond has more submerged plants, by entirely natural colonisation (in other words I didn’t plant anything) than you see in most garden ponds! But that story will have to wait for another day.