Soil Testing Guidelines for Urban Agriculture

Toronto Public Health has done an amazing job of creating guiding practices for soil testing for urban growers. I went to a workshop organized by Black Creek Community Farm as they are about to get their 8 acre site tested and are deciding how best to go about it.

Having worked at Sole Food, where the majority of our farms are located on former gas stations or parking lots, I was really interested in the soil testing standards that TPH came up with.

Originally they intended to do a literature review and see what guidelines existed in other major cities for urban agriculture. What they discovered is that most guiding practices for urban food growing were either non-existent or purely anecdotal and not evidenced based. And so they took on the project – reviewing all the literature and coming up with a framework that communities can use.

Soil testing can be very expensive – to do a full test of toxins can run you upwards of $3,000 per sample! And for a community garden, backyard grower, school food garden or urban farm – that can be a non-starter right there. Most groups couldn’t even afford one sample – and then consider that one sample wouldn’t even give you the information that you need.

The TPH guidelines have done a really great job of making the process less costly, trusting community groups to do the testing themselves (and not requiring a soil consultant to interpret the results), identifying what tests you can leave out and telling you when to not even bother testing your soil.

There is a general movement in this work away from the Safe/Not Safe dichotomy, which I totally love. In reality, we may go with worst case scenario and call a plot of soil “unsafe”, but in not growing on that soil we may be eliminating a lot of healthy behaviours and outcomes – someone growing in their backyard may mean their only access to fresh produce in their neighbourhood, a way to get exercise and physical mobility built into their day, the development of pollinator habitat, improved air quality, etc. Instead, we can inform someone of the risks, give them the tools to analyze the information and then make a decision for themselves. Someone’s need to eat may outweigh the risk of growing food in soils that are near a major arterial road.

And so, some soil testing basics that I love:

• Low Risk: If your land has always been residential, school, parkland, farm land or a child care centre and is not within 30 m of a major arterial road – don’t even test it. You will be ok. Wash your hands and wash your produce.

•  Medium Risk: if your land is within 30 m of a major road, or was ever part of a hydro corridor, commercial land, former landfill or in a lead reduction zone – you should get it tested. Unless – you land is really small (13 ft x 13 ft), then raised bed gardening will cost you less than getting your soil tested will.

• High Risk: If your land was ever industrial use, a gas station, a dry cleaner, an auto body shop, etc. then don’t even get it tested. Isn’t this one a revelation! You know already that it is going to be laden with heavy metals and lots of other nasty stuff – so you will pay $2000 (minimum) to get all your tests and find out that it is full of nasty stuff (which you already know!) So TPH recommends – just do raised beds.

And the ultimate thing to remember: do what makes you feel comfortable. We talked about how the Black Creek Farm is probably medium risk as it has always been farmland (meaning its safe) but it’s right up against Jane St (a major road.) So you as an individual could choose not to get it tested if you feel comfortable with those risks. But the farm will be selling its produce to the community and hosting lots of school groups for educational tours – and to feel comfortable, they are getting the soil tested. Point is, folks should be informed and then act based on the knowledge they have and their own comfort with risk.

What to test for?

Heavy metals and PHA’s. That’s it! The research shows that these are the things to be concerned about when considering produce nutrient uptake vs. other vegetation you may grow. You do not need to test for the whole sweet of toxins ($3,000 per sample), instead just ask for heavy metals and PHA’s and you should be able to find a $150-$200 price per sample.

TIP: The more samples you send in, the lower the per sample cost. So, find some other farmers, growers, community groups that will gather samples on the same day as you. Label them all well and send them in as one test.

So good! Here is the link to the TPH report. They are looking for feedback on their work and are hoping to develop a “train the trainer” model so that community members can get this information out to growers. Such good stuff.