Lawn fertiliser and its effect on water

Q. I am fertilising my lawn, but have concerns about the fertiliser going into my dam – can you help?

Answer:

Yes you should be concerned as most lawn fertilisers contain Nitrogen and Phosphorus which lawns require to grow.

But unlike lawns both Nitrogen and Phosphorus are bad news for water body’s like your dam or pond. And commonly these find their way into water body’s via run-off. So if you are watering your lawn this may cause run off into your water body, or a heavy rain fall will cause run off. We talk about how to reduce the likelihood of this.

Algal blooms need Nitrogen and Phosphorus to grow if you have excess of this going into your dam or pond then the algal blooms will florish. As the algal blooms take over the water body, they naturally reduce the oxygen levels in your dam or pond water and can result in fish deaths. Fish need dissolved oxygen which they absorb directly through their gills into their bloodstream, without this sadly they will die. As the algal blooms multiply, they encourage growth of bacteria which naturally increases the toxin levels, making it dangerous for both people and animals.

How to deal with run-off

So how does run-off occur, rain water will pick up these nutrients which haven’t been absorbed by the lawn or plants. Even lawn clippings can have fertiliser residue, so best to remove these from the lawn once mowed.

Try to not cut your lawn so short, as longer grass will help to prevent run-off and naturally absorb more water also if you can try and not fertilise near your dam water.

If you cannot prevent run off then look at installing aeration into your dam, this will keep movement in the dam water and helps to increase oxygen levels, which helps reduce algal bloom infestations. Or treat with Phoslock which permanently binds excess phosphates, which limits algal reproduction.