Sunday, 26 February 2017 15:00

Thankfully, everything you need for organic gardening – seeds and seedlings, bags of soil and potting mix, fertilisers and compost – is all readily available. So jump to it and get your organic garden on, right?

But what if you’ve recently acquired an existing veggie patch? You’ve just bought a house, moved into a rental property, or perhaps taken over your in-laws’ old garden. Unfortunately, these places don’t come with “I’m organic” soil labels!

Not knowing the integrity of one’s soil struck a chord with me. How could I put effort into sourcing and researching the organics in my life and fall short at knowing what my veggies are drawing from this unidentified soil? I shudder to think back to inner-city houses I have rented with gardens that appeared to be a few layers of soil over a bed of building waste. (I think I even grew up with one of these gardens, created by my dad while building our house!)

If you’re in the same boat and feel like you’re off to the gardening equivalent of a false start, take heed – all’s not lost and there are some great resources and remedies at hand.

VegeSafe soil testing

This is the ultimate resource for soil testing in Australia. Run by the environmental science staff at Macquarie University, the VegeSafe program provides free soil testing to check for heavy metals, which in high concentrations can be harmful to humans. These include arsenic, cadmium, chromium, copper, manganese, nickel, lead and zinc. According to their largest body of research conducted throughout Sydney, lead has been established as the most prevalent toxin, found to exceed recommended levels in 20 per cent of gardens.

It’s worth a visit to the VegeSafe website, where they provide plenty of information, as well as simple instructions on how to collect your soil samples and where to send them for testing. In addition to providing you with your soil report, they’ll also offer advice on what to do next, should you find yourself facing high levels of contamination.

Build a raised garden bed

If you want to jump to it and avoid the unknown legacy of existing soil, you could build a raised garden bed.  This way you control the soil content from the get-go. You’ll also have control over what materials to use in the construction of your garden bed, and thus ensure you’re not inadvertently adding toxins back into the garden. Steering clear of treated or painted timbers is your safest option for this. Pine timber, for example, is generally treated to promote longevity, as untreated it would rot away. You may be better off paying a visit to a timber salvage yard before a hardware store, and sourcing untreated hardwoods. Recycling bricks or pavers is another sustainable option.

If you’re building your raised garden bed over an existing site, you may also consider laying down a geotextile barrier (a permeable fabric barrier for use on soil). This will separate your new layer from the old, and will still allow water to pass through. I would suggest searching “organic” when checking out your geotextile supplier’s listings, as there seem to be many synthetic industrial-strength versions, which sound as chemically confusing as the toxic soil you might be barricading from!

Remove and replace the existing soil

While this is an option, be sure to consider the source of possible contamination in the first place to ensure that you’re not setting your new garden up for more contamination. Gardens adjacent to painted walls or beneath the roof drip line may contaminated due to their location – in which case, starting a new garden in a different site with new soil and using a geotextile liner might be the best option.

Mulch over soil

If you’re concerned about toxicity from an area of garden (pending soil testing), laying mulch (such as bark chips or pea straw) over the soil to keep dust contained is a good start. It’s also good garden practice in any case, as it helps with water retention and promotes biodiversity. 

While a clean bill of soil health would be ideal, the upside in making the necessary adjustments is in knowing that your organic gardening journey is off on the right path. Good luck!

Words and image by Anoushka Gourlay from Hey Ho, Let’s Slow.