Garden hazard_1

Tyres may seem handy to grow food in but they are one of many health hazards found in school gardens.

There’s a lot to consider when setting up a new garden – what soil to use, which plants to grow and how to maintain the garden. But just as important are the type of materials you use to build the garden and prepare the soil, especially when it comes to the health of your garden and students.

Car tyres can leach cadmium and other heavy metals into soil as they weather and should never be used for garden or compost containers. If your school is using tyres as food growing containers, you could keep the tyres in place for growing non-edibles but grow food plants in uncontaminated soil.

Treated timber is not recommended to be used as edging for garden beds in schools due to concerns about the leaching of chemical products, including arsenic (a known carcinogen), in the treated timber onto the timber surface and into the soil. Some alternative timber preservation methods contain pesticides, while others leach copper or boron and also are not considered appropriate in school gardens.

Natural fibres in carpet and carpet underlays are treated with persistent pesticides and many carpets contain toxic chemicals. If used to cover or suppress weeds, when exposed to the elements, chemicals from these products can leach into garden beds, compost and worm farms. Thick weed matting can be used to suppress weeds and if you are building a no-dig garden, see Curriculum Materials – Topic 3, From the Ground Up for information on preparing the ground to make an ‘instant’ and easy garden.

Getting manure from a local farm or racetrack?

Garden hazard_2When it comes to preparing the soil for planting, it’s wise to check the origin of the compost or manure. Make sure the compost does not come from pastures sprayed with pyridine herbicides and that manure is not from animals that have grazed on sprayed pastures. The herbicide remains active in both the mulch and the animal that has grazed on sprayed pastures until the chemicals are broken down by microbes. To avoid herbicide and general hygiene risks, use only well-rotted manures broken down through aerobic composting or purchase compost registered for use in organic farming or gardening. For composting methods and activities, see Curriculum Materials – Topic 2, Living Soil.


Herbicides should never be used to clear the garden area of weeds or other vegetation as they kill or inhibit a range of soil organisms, increase the incidence of soil-borne diseases and impact on the health of soil, humans and other animals. Many shelf-bought herbicides contain an active ingredient called glyphosate, a toxic weed killer linked to non-Hodgkin lymphoma, and other ‘inert’ ingredients linked to human cell death, particularly embryonic, placental and umbilical cord cells. Be sure to check if your school is using these products on any part of the school grounds. Organic weed control uses physical methods such as weeding, mulching and grazing, and also the use of safe products registered for use within organic systems.

Australian Organic Schools is compiling a list of safe products to use in organic gardens so you don’t have to worry about whether you are buying something that’s bad for your health. See Garden Products for more information and if you have a favourite product registered for use in the organic garden, please email to see if we can add it to the product list.

Click here  to read about the how the Australian Certified Organic Standard outlines the minimum requirements for certification of organic or biodynamic produce and takes a whole-of-system approach to the health of people, animals, plants and soils. This is a good resource for making sure the products you use in preparing and maintaining the garden won’t compromise the health of your garden and students. When you see the Australian Certified Organic Bud logo on a product such as organic compost, you can be reassured that its product ingredients have been certified to the Standard and have met rigorous certification checks.

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  • I used to garden with car tires to good effect.

    Before any chorus starts up, here is an article about the main environment concerns about auto tires in contact with soil: used as a garden mulch.Also there's this aside:
    But---What about food production? Creating raised beds out of used tires and growing vegetable crops.
    Tires around soil as a raised bed garden has been used by many people. I  have not heard of problems from that, but the surface area in contact  with soil is small. In the short term, it may be little problem. But eventually the rubber degrades, Zn gets in the soil, and if the soil pH  is 6 or below, uptake may be too much. Again, the higher the surface  area, the more rapid the release of Zn and toxicity observation..Toxicity to plants from ground rubber used as a mulch  or a component or potting media, or burned tire residues in soils, have  killed a wide range of plant species.(ref)
    My point is that using tire rubber as garden bed walls is not a massive exercise in toxicity. Over a very long time you will get break down, of course, and some leaching, but I fail to see how that is so extraordinary compared to the massive , and much larger, scale of pollutants that permeate any urban existence. Tire rubber, still integrated with the original  tire, and not desiccated or pulped, is a useful, free, generally stable material that would  mostly creates a huge disposal problem. It resists termite attack and doesn't collapse or, for that matter, rot away. When cut into strips it can be flexed and joined  into different garden bed designs.
    I can afford to be smug: I don't drive or own a car. I was  doing my practical bit so the car drivers can drive on oblivious to the toxicity generated of their everyday activity. 
    In my limited front yard very small space, the tires were very effective and  functioned akin to the principles of square foot gardening:


  • After all the excitement about the styrofoam self-watering box system at Spurtopia, I had to do some reading because I could not shake the feeling that it is not right to grow food in polystyrene, besides the fact that it looks quite ugly. It turns out it is quite toxic and yes! leeches chemicals in the soils. I can't afford expensive pots. For me it defeats the savings from growing my own food so the brain has been ticking since this major disappointment and I am working out a new system where the polystyrene does not touch the food, soil or water. I figure if I use upside down box to hold the pots above water (Kratky style) over the top of another container to keep the water from evaporating and use old bits of sheet as wicks for those plants, which don't grow big roots. (just lost my oregano which should really grow like weed) I think I'll start a separate discussion about non toxic container once I finished my prototype.

    • Well there you go, I did wonder. Thank you for doing the research for us Valerie.

      Show us what you come up with in the end won't you.

    • Oregano likes dry conditions with perfect drainage - as do Lavender, Rosemary and Pennyroyal. Hmmm, didn't know about the styrene leaching toxins - yecch. I use sheets of styrene inside my bins to shield the roots from heat. I'm interested to know what your research and experiments reveal.

      • Thanks Elaine. It seemed to die from drying out completely :\ I think I might rehouse the survivors in the normal beds. 

        I thought I should mention also that polystyrene in the heat is definitely not good either. I plan on covering mine with the rest of the old sheets or jute bags.

        • In an earlier version of our garden here, we used Styrene boxes. Elaine painted them on the outside using 'water paint' or 'plastic paint' which kept them from breaking down quite so soon and made them look a little less like ex-fruit boxes. Perhaps the same paint - or a more natural paint - could be used on the insides. Oil paint dissolves the Styrene so I hear. Whether natural paints are oil-based I don't know.

          Putting old sheets inside the bins before filling them with mix sounds like a quick and simple solution.

          • I like the idea of using some sort of natural paint for lining.   At the workshop Roman commented that results so far did not indicate detrimental health benefits from leeching, but there is still further research going on with this issue (that's from my memory, not always accurate these days!)

            • The effects of leeching might not always be obvious. How would you know what to look for?

  • A stronger version of Roundup has just been registered and approved by the APVMA, normal Roundup contains 360g/L glyphosate, the new stuff contains 520g/L glyphosate. 

    Product Name:
    Roundup Dura Herbicide By Monsanto
    Active Constituent/s:
    520 g/L glyphosate (present as the potassium salt)
    Applicant Name:
    Monsanto Australia Ltd
    Applicant ACN:
    006 725 560
    Summary of Use:
    For control of many annual and perennial weeds
    Date of Registration:
    31 March 2014

    Getting ready for more "Roundup Ready" GM crops?.  Some sorghum crops are now being defoliated by Roundup, prior to harvest.  The poison is actually sprayed on the crop, not the weeds, so that residue is getting into your chook food.  The only way to stop all this is to pay more and buy organic - everything. 

    • I just found out that the sorghum spray is Roundup Ultra Max, which is even stronger at 570g/L glyphosate.

      Birdy num-nums indeed!

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