General Info, Landscaping -


Recently I visited a landscape design client of ours where the client had (after many years) re-mulched the garden beds and topped up the garden soil in a few spots with some bulk garden soil from a local landscape yard.

The very first thing that struck me (after the reaffirmation of the positive effect that fresh mulch can make on garden aesthetics) was the nutgrass.

Even though it was late autumn and the soil had only been in place a few weeks, nutgrass was already starting to poke through the mulch.

Only in the spots where the new garden soil had been placed.


Brisbane City Council have a very useful online weed identification tool where they describe nutgrass as a “very troublesome weed”.

I would suggest that Brisbane Council are masters of the understatement!

Although strictly speaking it is not a grass but a form of sedge, nutgrass (Cyperus rotundus) is definitely nutgrass by name and nutgrass by nature!

It's really annoying to have to deal with.

It gets it’s common name from the nut-like tubers found on the rhizomes of the plant under ground which serve as energy storage for the weed.

It is one of the most invasive weeds known and is difficult to eradicate, especially if you let it get away on you.

And as far as invasive goes, nutgrass density has been recorded as high as 5000 shoots/m2 in extreme situations!

The distribution range is extensive along the Eastern Seaboard, especially from mid-coast NSW through to past Hervey Bay in Queensland.

Although it is found in more temperate climates, in these areas you may find that Yellow Nutgrass (Cyperus esculentus) dominates.

And as you head inland into the heart of Australia the incidence of nutgrass declines.

Normally, nutgrass contains 85% moisture, in dry conditions if the moisture content dips below 15% the plant can’t survive.

This may be why its historical distribution range falls away the farther inland you go.

It also shows that it really does enjoy wetter conditions, so given another wet summer is being forecast, nutgrass right now is going “viva La Nina”!

If you have nutgrass on your property, you may find that (if it’s in a garden bed where you can spot spray it without killing other plants) repeated applications of Glyphosate (Round Up or similar) may ultimately kill it.

In turfed areas or heavily planted garden beds, you will need to use a selective herbicide containing Halosulfuron-methyl such as Sledgehammer or Sempra.

But again, don’t expect a 100% kill from the first application.

The other alternative for the home gardener is digging it out (if it’s in a garden bed as opposed to turf), but that only works if you get everything which may mean digging to a depth of up to 400mm and ensuring every single nut is removed!


So, why did it start to grow out of the freshly imported garden soil at the client’s property?

There are a couple of possible reasons.

Firstly, nutgrass is incredibly heat tolerant, and the composting process on the organic matter used in the manufacture of the garden soil needs to be undertaken correctly ensuring the right temperatures are maintained over the right period of time to ensure weed seeds are killed.

Reputable manufacturers will test the temperature of their compost weekly to achieve this.

Also, the topsoils that might be accessed for use as a component of the garden soils may have nutgrass present and there is no thermal treatment for this component of the product to kill the seed.

I know of one manufacturer that is incredibly pedantic on this issue to ensure that the raw material they are receiving is nutgrass free.

They also perform multiple tests weekly (including temperature) on their compost.

So, with our clients garden soil blend, I would suggest that either one or both of these issues was present during manufacture.

And I can confirm that the garden soil was not sourced from the manufacturer I allude to above and I would suggest that given their QA procedure it is highly unlikely it would be.

The bottom line is, though, if you’re buying garden soil from a landscape yard, it might not be enough for a sales person to simply maintain their product is nutgrass free.

Rather, be prepared for the eventuality that nutgrass is present and deal with it immediately it becomes apparent.

Which, in the right conditions, won’t take long.

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