In March this year I took 3 samples of soil from the garden to be tested as part of the EPA’s GardenSafe program. I was already doing this for my Newstead home garden, so offered to do it for NCG also. I took samples from 2 of the Diggers beds and the 3rd from under the pear arbour – where there seemed to have been less soil improvement, therefore probably closer to the original garden soil. The samples were tested and analysed for common garden contaminants: Arsenic, Cadmium, Chromium, Copper, Manganese, Nickel, Lead and Zinc.
The results were pretty good. We certainly had no problematic levels of garden contaminants – all were well below the safe garden level known as the “HIL A” standards (Health Investigation Levels for gardens with accessible soil.) All the soil samples were rated as “Clay Loam”, but the pear arbour had more sand and less clay than the other two. I did notice that the pear arbour had the lowest level of all the contaminants (less soil additions over the years?) but the highest level of Lead (103 mg/kg, still under the 300 mg/kg of the HIL A guideline.) Is there anything about the iron garden sculpture, its welded joints or any paint applied to it that would account for the relatively high level of lead?
The other thing I noticed is that the “total organic carbon” rate of 3-4%, which is the measure of soil organic carbon – seemed fairly low to me as it was on par with my own garden results. I was surprised about this considering how much compost has been used over the years to improve the soil at the garden, whereas I have only been improving my soil at home for 18 months. My soil generally does not have the crumbly texture like the garden’s soil. Does anyone know what is ‘good’ level of soil organic carbon for growing veggies? The report did not provide a guideline or benchmark level.
Lastly, does anyone know what a “good” rate of Potassium and Phosphorous is for growing veggies – greens vs root crops? I’m not sure if we have the magic combo. I note the pear arbour had more Potassium (10,710 mg/kg) than both the veggie patches (7778-9412 mg/kg )– not sure why or if that’s a problem. Phosphorous was in the range of 2603-3276 mg/kg for all 3 beds, which seems pretty similar.
I will test the Ph when I’m next at the garden, and see if it is under the 8.0 of recent testing.
Sarah Lambert
The full report of the EPA GardenSafe testing can be found here.
in the garden 