Removing Horehound weed with Friends of Mount Majura (FoMM)

As a part of my volunteer work experience I joined the Friends of Mount Majura (FoMM) volunteer team to assist with some essential conservation activities, one of which involving the removal of horehound (Marrubium vulgare), an invasive weed species that infests a number of sites on the ridge between the Mt Majura Nature Reserve (MMNR) and the Mt Ainslie Nature Reserve (MANR).

The Horehound Blitz weeding upon the Mt Majura Ridge was paired with marvellous views of Majura valley and north Canberra.

Horehound is widespread across Australia after being introduced from Europe, the Middle East and northern Africa during the 19th century as a result of livestock grazing. It is therefore abundant in nutrient rich soils and areas of high disturbance due to overgrazing. After speaking with one of the FoMM volunteers, Waltraud Pix, it became evident that grazing, particularly of sheep, is the primary culprit for the presence of horehound on the ridge. The sheep migrate to the ridge where they prefer the warmer temperatures and sunlight during winter and cool breezes during summer, consequently dispersing their droppings in a concentrated area to produce patches of weed prone soils containing high levels of nutrients. After being introduced to the causes and impacts of horehound, we set off with our spades and pickaxes to remove as much horehound as possible!

Horehound weed (Marrubium vulgare) removal in action.
Post-removal of horehound weed (Marrubium vulgare) after using my trusty pickaxe.

As illustrated in week 9, weed infestations have the capacity to destroy native habitats by completely transforming natural ecological systems. Invasive weeds such as horehound are thus increasingly problematic to the Australian landscape by threatening native plants and wildlife. However, there are some feasible impact prevention management activities occurring that aim at supressing horehound infestation for good.

In addition to ongoing weed removal by FoMM and Park Care volunteers, I was introduced to an alternative weed management treatment currently in place at the Mt Majura ridge. This involves placing a thin layer (<100mm) of organic mulch over an infested soil patch to assist in the regeneration of native grasses, herbs and shrubs. Since invasive plants prefer nutrient-abundant soils and natives do not, the theory of one of the FoMM volunteers, Waltraud Pix, is that the mulch acts as a protective layer for the soil beneath by retaining moisture and basic nutrients that native plants prefer. Soil microbial processes of decomposition and nutrient cycling are then expected to take up any abundant soil nutrients, leading to a patch of soil that is less prone to weed invasion while also reducing the use of harmful pesticides. The mulching treatment had been implemented on the patch that we were weeding on the Mt Majura ridge around 6 months ago, and so the FoMM volunteers are closely monitoring the site to assess its short and long-term effectiveness.

Small patch of organic mulch treatment covering the horehound infested area upon the Mt Majura Ridge, along with one of our many piles of removed horehound weed.

Despite countless efforts of weed management and native regeneration by the FoMM Park Care volunteer team, they have encountered many limitations due to limited government funding and stakeholder engagement. I was informed by FoMM volunteers that they are very reliant upon the involvement of the community, however their conservations efforts should be further supported by the funding and awareness of the state and federal government. Nonetheless, the FoMM Park Care group are determined to encourage more communities and stakeholders to be actively involved in their conservation work while improving the quality of native landscapes and assisting in the conservation of wildlife across the Canberra region for years to come.


Australian Government, 2019, Impact of Weeds, Available from: Weeds in Australia – About Weeds, (Accessed 20 October 2019).

Callaway, R.M., Thelen, G.C., Rodriguez, A. and Holben, W.E., 2004. Soil biota and exotic plant invasion. Nature, 427(6976): p.731.

Camenzind, T., Hättenschwiler, S., Treseder, K.K., Lehmann, A. and Rillig, M.C., 2018. Nutrient limitation of soil microbial processes in tropical forests. Ecological Monographs, 88(1): pp.4-21.

Coutts-Smith, A. and Downey, P.O., 2006. Impact of weeds on threatened biodiversity in New South Wales. Adelaide: CRC for Australian Weed Management.

Downey, P.O., 2006. The weed impact to native species (WINS) assessment tool–results from a trial for bridal creeper (Asparagus asparagoides (L.) Druce) and ground asparagus (Asparagus aethiopicus L.) in southern New South Wales. Plant Protection Quarterly, 21(3): p.109.

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Weiss, J. and Sagliocco, J.L. 2000. Horehound (Marrubium vulgare): a comparison between European and Australian populations, Plant Protection Quarterly, 15(1): 18-20.

Wilson, P.D., Downey, P.O., Leishman, M., Gallager, R., Hughes, L. and O’Donnell, J. 2009. Weeds in a Warmer World: Predicting the Impact of Climate Change on Australia’s Alien Plant Species Using MaxEnt, Plant Protection Quarterly, 24(3): 84.

Posted by U6382550

About Biodiversity Conservation Blog

I am an Associate Professor at The Australian National University and convene a (very awesome) course called Biodiversity Conservation. Myself and students in the course contribute to this blog.
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