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. 

Building a Farm

Our largest site is located at Pacific & Carrall, right next to the sea wall in False Creek. The land is a parking lot owned by the condo company Concord Pacific. We get the land for free and they get a tax incentive for donating the space. We also get a nice view of the backstage buses for all the concerts at Roger's Arena - we had front row seats for a whole day of Bieber fever. In total, we have 2 acres of production on this lot. 

At our first site we constructed 18 inch raised beds out of lumber, but for this expansion we needed a way to build a lot of beds in a short amount of time and on a tight budget. Seann and Michael went through many designs and considered lots of repurposed materials, eventually landing on this design. 

Each box made up of a used pallet which is covered in stapled landscape fabric (you can see the black fabric in the bottom of the image above.) The fabric acts as a way of keeping soil from falling out the bottom. We then used shipping collars to act as the side walls of the container. These collars are used in the shipping industry and are the same dimensions as a shipping pallet. They are hinged and can be laid flat and stacked. They made the set-up of the beds real easy - we would drag over pallets, line them all up, roll out the landscape fabric, staple and cut, and then pop on a shipping collar. For 2 acres of space we had to set out 3,000 boxes. It took our team of about 20 staff 2 weeks to lay out the whole site.

We set up the rows so that they were in blocks - around 20 rows in each block. The irrigation is also set up in blocks so that we can turn on the drip for just one block at a time. This also makes the crop planning simpler as we can plant blocks at a time, and then rotate crops from block to block each season.

The soil was another story. To fill 3,000 boxes with a yard of soil would have taken us weeks to do by hand, so we had a soil blower come in to fill the boxes. It's a giant truck with a huge hose attachment that blows out soil - real noisy but real fast.

Our first harvest day at the Pacific Site! Greens were the first crops ready.

Prepping & Amending Beds at SOLEfood

Prepping beds for new plantings is one of my favourite tasks. The farm has a really thorough planting schedule – lots of succession planting ensuring that there are crops growing throughout the whole year, not just the standard growing season. In the height of the summer we are doing twice a week seeding of lettuces, arugula, asian greens and radishes. We also do continual plantings of carrots, beets, dill and cilantro. As the weather cools, we were seeding lettuces once a week, and also transplanting some starts of hardier greens like kale, collards, chard and purple sprouting broccoli.

Prepping Beds

After a crop is done producing, we pull out the finished plants, roots, and dead leaves (crop trash). The soil gets turned over with a digging fork and all the soil clumps broken up with a rake or by hand. It’s important to pull out all of the roots because they get stuck in the seeder really easily and jam up the wheel – otherwise they wouldn’t be such a big deal to just leave in the bed. Once all the clumps are broken up we either rake or level out the bed by hand to make sure it’s nice and flat – again, easier for the seeder.

Bloodmeal sprinkled on half a row - in the beds further back
you can also see the darker worm castings that were applied.

Amending the Bed

Plants require three primary nutrients – nitrogen for healthy leaf and stem growth, phosphorous for root growth and potassium for overall plant health. There are other micro nutrients needed by plants, but these are the big three. Crops are generally removing these nutrients from the soil as they grow. This is how our food becomes nutritious – healthy soils mean healthy food. This means that after each planting there are fewer nutrients available in the soil for the next succession. If we just continued to plant, we would loose our soil fertility and run into serious problems with plant health.

In lots of conventional farming operations, you would counteract this nutrient loss with the application of synthetic chemical fertilizers. But there are also some more sustainable and organic options. Ideally we would be turning in our own compost as a fertility source for our soils, but we are currently unable to compost most of our plant matter due to municipal bylaws. Also, as an urban farm, we really value space and therefore use soil amendments that have less bulk and take up little storage space. For us, that means instead of bringing in compost or manure, we use worm castings and bloodmeal.

Blood meal is dry, powdered pig’s blood or cow’s blood. It is very high in nitrogen, a nutrient that most soils are often lacking. There are other similar amendments - bone meal has a high phosphorous content and is made of powdered animal bones, feather meal is ground up chicken feathers and also has a high nitrogen content, and fishmeal is the same idea, ground up fish bones and guts. All of them will generally do the same thing, and all of them smell absolutely terrible. Make sure to keep all of these very dry as even a bit of moisture will cause clumps that are hard to break apart. If this does happen, be sure to beak up or remove any clumps before applying to the soil.

Worm castings are essentially worm poo – it is organic matter that has been digested by worms. The castings provide a source of nutrients and also provide a source of beneficial microbes to the soil, enhancing soil biology

Once a bed has been prepped we sprinkle one yogurt tub of castings per box and two yogurt tubs of blood meal per row (highly scientific calculations.) You want a light sprinkling of the blood meal – too much nitrogen will burn your plants. Once you’ve sprinkled your row, you can scratch in the amendments with a hand cultivator, or your hands. You want the amendments to be about half an inch below the soil so that they are available for the seeds and young starts to use.

You can then begin your planting!