Guide for Soil Testing in Urban Gardens

Materials NeededWe recommend testing the soil if the planned garden is on a Medium Concern site AND if the garden is larger than 13 X 13 ft. Testing the soil consists of tak-ing a soil sample, having it analyzed, and interpreting the results. It is not cost-effective to conduct soil testing for small gardens. This is based on estimates of the cost of soil testing versus building a raised bed garden.

Soil Sampling

Collect a representative soil sample of the site. A composite soil sample is made up of two or more combined sub-samples to represent an area of the garden. Use the following checklist to walk you through taking a soil sample.

Create a diagram and plan where you are going to take your soil samples:
• Make note of the name and address of the property
• Draw a line around your garden using pylons, tape or rope. The soil sample should be taken from the area that the gardeners use. A typical commu-nity garden will need only one or two soil samples. We recommend that a composite soil sample is taken every 10 x 10 to 15 x 15 m area (approxi-mately 50 x 50 ft). Starting at one corner of the composite soil sampling area, walk diagonally to the far corner and repeat, making an “X” pattern. Mark the location of a sub-sample approximately every 2.5 m (8 ft) using a pylon or some other marker. This is where you will take your sub-samples of soil that will make a sample. For gardens larger than half an acre, call 311 for help
• Note the location of the sub-samples on your diagram

Soil Sampling AreaSample the soil
• Strip off turf or other vegetation from the sub-sample spot
• Take shovel and dig into soil down to 40 cm (16 in) Place sub-sample soil into Bucket 1
• Break up and mix the sub-sample soil in Bucket 1
• Remove stones and visible debris
• Note the presence and type(s) of debris, smells, and staining in your field notes
• Transfer a trowel full of the mixed soil from Bucket 1 to Bucket 2
• Refill the hole with the remainder of the soil in Bucket 1, and replace the turf
• Repeat until nine sub-samples have been collected separately in Bucket 1 and transferred to Bucket 2
Create composite soil sample
• Mix the combined sub-samples in Bucket 2 to make the composite.
• Label sample bag with:
• name of site
• sample number
• sampling date
• name(s) of person(s) doing the sampling

• Transfer the mixed soil from Bucket 2 to the labeled sample bag
• Seal the sample bag and place it in a cooler with ice packs

Note: If you are creating more than one composite sample, all equipment should be washed with soap and water between the composite samples. There is no need to wash the equipment when taking sub-samples.

The laboratory will tell you how much soil you need. Typically, each composite soil sample is approximately 2 cups (2 small trowels of soil). Each la-boratory is different and prices change over time. You should expect to pay between $150 to $300 for each composite soil sample.

Soil Analysis

Purpose: Select a laboratory for the soil analysis and tell the lab staff what analyses you would like them to do.

Toronto Public Health has identified a list of the most likely contaminants present in Medium Concern sites. Use the following checklist to walk you through getting your samples analyzed.
Soil Analysis Checklist
1. Select a laboratory able to do the analysis
Find qualified labs in your area through:
• Yellow Pages (heading: Laboratories – Analytical & Testing)
• Internet search

2. Contact the Laboratory
Get in contact with your chosen lab several days before you take the samples to:
• Confirm price and turnaround time
• Obtain a chain of custody form. The chain of custody form provides information on you (the client), the samples, and the analyses that you want
• Tell the lab when you expect to deliver the samples
• Obtain instructions for handling the samples and delivering them to the lab
3. Fill out a Chain of Custody Form
Fill out the chain of custody form and keep the required copies with the samples
• Every lab’s form differs, but you will have to indicate that you want the soil tested for pH values, metals and PAHs. Write out the full name of each metal and PAH you want tested for
Contact the lab for advice if you have any difficulty with the form
Soil interpretation
• Ask the lab to interpret the soil samples according to the contaminants and the Soil Screening Values for urban gardening listed on page B-7
4. Deliver Samples to the Lab
The laboratory will provide instructions
Deliver or ship samples to lab within one day of sampling. Some laboratories will pick up the soil sample
Keep samples refrigerated or in a cooler between the time you take them and the time you deliver or send them to the lab