Wednesday, June 29, 2011

Sugar as an eco-friendly weed control? Food for thought

I've written several posts about pet and animal safety in our gardens. One entitled Pets and Pesticides specifically detailed some of the research done on pesticides and how the can affect animals. The other one, called More Pet Safety in the Garden, talked about some of the other items we use in our gardens that can also harm our pets.

So when I saw a post today called Pet Friendly Weed Killers by Lori Thomas on, I had to check it out and see if I could learn anything new. I did.

The article states that SUGAR can be used as a pet-safe weed control. Since I had never heard that sugar can control weeds, I did a little more research to see if I could track down a reputable source for that statement.

Here are some excerpts form a study carried out at Charles Sturt University in Australia in 2005:

By Margrit Beemster, December 2005. 

Sugar has the potential to control annual weeds according to recent research trials conducted by researchers from Charles Sturt University. The researchers, ecologists Dr Suzanne Prober, Dr Ian Lunt and Dr Kevin Thiele, have applied sugar to trial plots for a project funded by the NSW Environmental Trust on how to restore understorey species in endangered Grassy White Box Woodlands. 

The researchers have found that sugar provides a good, short-term non-chemical and ecologically friendly method of weed control. "It appears sugar is a tool we can use to help change a system back to one dominated by native species rather than weeds,” says Dr Suzanne Prober who has been working to conserve and restore grassy white box woodlands for the past 15 years. Nearly all of the woodland belt, from southern Queensland to north-east Victoria is now used for agricultural purposes, principally wheat and sheep. 

So why does the sugar work? Because it is one of the fastest ways of reducing soil nitrate levels. Dr Prober’s compared soil nutrients in undisturbed woodlands and disturbed, degraded sites. She found the most striking difference between the two was in nitrate levels, which were extremely low in undisturbed remnants and high in degraded remnants. 

“It seems that many of our weed problems are due to high nutrient levels”, says Dr Prober. “There is an enormous amount of information on how to increase soil nitrogen to improve crop growth, but very little on doing the reverse. However there has been some research done overseas where sugar was used to tie up nitrogen levels for a short time.”  

The researchers, who spread half a kilogram of refined white sugar to each square metre of soil every three months, found this inhibited weed growth of most annual weeds giving the native plants the opportunity to become well-established. However more research is required to work out the optimum rate of application. “We realise that the sugar levels we used in our trials would not be economic to use over broad scales”, said Dr Prober, “but at the moment we don’t know if we would get similar results if we used less sugar or if we used cheaper alternatives such as molasses or sawdust”. 

So how does sugar reduce soil nutrients? “When sugar is spread on the soil, it feeds soil micro-organisms, which then absorb lots of soil nutrients as they grow,” explains Dr Ian Lunt from CSU’s Institute for Land, Water and Society. “The micro-organisms then hold these nutrients so the weeds can’t gobble them up. In effect we are ‘starving’ the weed species that require lots of nutrients to grow.” The lack of nutrients stopped the weeds from growing large, allowing the native plants, which can grow well in low nutrient levels, to grow bigger and faster. click here to read rest of article.

Whether or not sugar is a viable alternative for most of us in our search for earth-friendly ways to control weeds may require further research. But any method that adds fewer toxic chemicals to the ground certainly sounds like a sweet one to me!


  1. This is interesting, but I wonder about its application to North American situations and soil types. So much of the Australian land described in the article is dry, much drier and sandier than the average Middle Atlantic, even in the coastal plains.

    It is worth noting that some of our native plants have become quite invasive in Europe and Australia, and that some of the research conducted on North American invasive non-native weeds, especially out west, found that soil played a much larger role than originally expected.

    Also, interesting to consider what sugar's potential effect on insect species would be in areas where it might be used in broad application. Would this give some species an unexpected and unwanted upper hand?

    Interesting, however, and so I'm off to google around and find out more about this… thanks for the interesting article…always love that science….

  2. Hi Alison. Excellent points. Your comment reminded me of what I see as a huge problem with today's information overload. There is just WAY TOO MUCH information available out there and it all really needs to be taken with a grain of salt. It's easy for readers to pick up just bits and pieces of information on the internet and assume it is true without researching it further. After I read the first post, I found many other articles on-line listing sugar as a good weed control, but only a few of them referred back to the original study for more details. I like to use for reliable information as well as google scholar.

  3. That's nice to know. My dog is always playing on the backyard and I really don't want him to get poisoned with pesticides. On the other hand, I don't want to refuse to them and thus turn my backyard into jungle. Sugar is a good way out in my situation cause I don't have to sacrifice neither my pet's health nor aesthetic look of the garden.


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