Plant Doctor Archive

Water Gardens — Oxygenating plants

HOW many oxygenating plants should I have in my pond?

THIS is a very hard question to answer accurately. Despite the name, you should not rely on these plants (which I prefer to call deep water aquatics) for oxygen in your pond. It is true that all plants produce oxygen during the day, but they also produce carbon dioxide at night.

If you have a lot of plants then you can run the risk of oxygen depletion and carbon dioxide poisoning of your fish. This is actually quite common at this time of the year, as warm water naturally holds less oxygen than cool, exacerbating the problem.

The cure is to circulate the water using a fountain or waterfall which will oxygenate and drive out the CO2. Of course, if you are doing this you do not need to rely on the plants for O2!

The other reason to grow these plants is to help with water clarity. While theoretically possible to do this, I have found that in NZ it is quite unreliable. You are much better off generally to take care of water quality with a good filter system.

Therefore I suggest that you plant your pond to suit your taste. Some people like lots of plants, some not so many. Having said all of this, the common formula used by landscape gardeners is five plants per square metre of surface area. I hope this helps!

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.