Practicing Safer Soil: Growing in the City

When you are planning a new garden in the city it is important to consider the health of your soil. Because of industrial practices over the years, natural soil chemistry, motor vehicle emissions, and lead and zinc in old house paint for example, some of our city’s soil is contaminated. So when you are ready to start planning your new garden, it is important to test your soil for common contaminates so that you can have a clear idea of the health of your soil and make informed decisions that feel safe for you and your community. This post will explain a little more about how to test your soil, and how to plan your garden accordingly.

Soil that is considered contaminated is soil which has levels of a particular element (such as lead or arsenic), that are higher than the Canadian Council of Ministers of the Environment (CCME) guidelines for agricultural use.

There are two kinds of soil tests. The first is to test your soil for its nutrient contents, and the second is to test for heavy metal contaminants. Here is a little bit of information about how, when and when to do each of these tests.

Nutrient Testing

The Nova Scotia Soil testing Lab, located at the Nova Scotia Agricultural College, will test your soil for organic matter, acidity and other essential nutrients (but not heavy metals). This test will help you decide how much compost you need to add, as well as other soil amendments to boost the fertility, neutralize the pH and condition your soil. 

When To Sample

Soil sampling should be done in the fall, after the crop has been removed. Sampling in the early spring, when the water level is high, can cause misleading analysis, especially for pH and lime requirement. In order to be sure that you get the proper analysis for your soil, they must know what you are (or are hoping to) grow.

How to Take a Soil Sample

Step 1: Obtain soil sample boxes and sample submission forms from the local field office of the Nova Scotia Department of Agriculture or from the Quality Evaluation Division, Laboratory Services in Truro.

Step 2: Take a garden trowel and go down 12 to 15 centimeters (5 to 6 inches) in 6 to 10 different areas of your garden or flower bed.

Step 3: In a clean bucket or pail, empty the contents of each area. Remove plant debris. After you have done this, mix the soil together.

Step 4: From this mixture, take a 500 mL (2 cup) sample. This sample will be a good representation of the garden or flower bed soil.

Step 5: Place the 500 mL (2 cup) sample into the box. If you do not have a soil box, a freezer bag that can hold the full sample of soil can be used.

Step 6: When you receive your soil test results, consult your local agricultural representative or specialist about recommendations.

Payment and Shipping

Cost is $20.50 per sample + Disposal fee + HST.  A cheque or money order made out to the Nova Scotia Department of Agriculture must accompany the soil sample. If you are mailing the sample, please address your package to:

176 College Road, Harlow Institute
Truro, NS   B2N 2P3

Heavy Metal Contaminants Testing

You can get your soil tested for various contaminants if you are worried about or unsure of the health of your soil. In Halifax you’d likely want to test for Lead, Arsenic, Copper and Zinc.

Where to Send Your Sample

Daniel Chevalier,                                                                              

Manager, Minerals Engineering Centre
Dalhousie University
1360 Barrington Street
GH Murray Building, Room G101
Ph: (902) 494-3955

AGAT Laboratories                                                                               

11 Morris Drive
Dartmouth, Nova Scotia
Tel 902-468-8718
Fax 902-468-8924
Toll Free 1-888-468-8718

MAXXAM Labs                                                                                                       

200 Bluewater Rd., Suite 105, Bedford, NS B4B 1G9
Tel: (902) 420-0203 or (902) 832-4852
Toll Free: (800) 565-7227

Reading Your Results

The CCME soil quality guideline for agricultural land, is a baseline for what acceptable levels of each of these metals are in your own garden. These are all measured in parts per million (ppm) and are as follows:

 

Arsenic

Copper

Lead

Zinc

Maximum acceptable concentration for agricultural lands – ppm

12

63

70

200

pH measures if your soil is acidic, alkaline or neutral, indicated by numbers from 0-14 with 0 being extremely acidic and 14 being extremely alkaline (“basic”). Most plants prefer a neutral soil, somewhere in the range of 6 – 7. Keeping your pH neutral helps to make nutrients available to your plants, it also helps to “lock-up” heavy metals in your soil, making them less available to your plants.

Organic matter refers to the plant and animal materials that exist in the soil. It is important to be constantly adding organic matter to improve soil structure and replace micronutrients that plants need to thrive. According to Nova Scotia Department of Agriculture, a good organic matter concentration is greater than 3.5%.

Gardening in Contaminated Sites

If you’re not sure, or you know that your site is contaminated, you can build raised beds and bring in clean soil from elsewhere. There are lots of ways to do this:  building a box at least 6 inches high out of scrap wood or stone tiles and laying a sheet of landscaping cloth along the bottom. Food-safe plastic buckets salvaged from grocery stores also make great container gardens. 

If you’d rather work with the soil that already exists on your site, there are lots of ways to reduce possible health risks. We reached out to professionals and urban farmers across Canada and the United States to ask their opinion on mitigating the risks of contaminated soils, and together came up with the following recommendations:

  • “Eating dirt” is by far the most significant way that heavy metals enter the human body. Wear gloves if possible, especially if you’re gardening with children. Clean your hands afterwards and wash produce carefully.
  • Avoid weeding on very dry days, or use the “chop-and-drop” method where you cut young weeds just above the soil and let the greenery fall to the ground as mulch.
  • Since a little soil sticks to roots, peeling root vegetables and growing lots of leafy greens and fruits is a good approach, just wash them before you eat them. 
  • Last but not least, adding organic matter to your soil reduces the amount of contamination that is taken up by your body and dilutes what exists in the soil.  Similarly, adding wood ash, lime, or egg shells to make the soil less acidic reduces heavy metal absorption in humans. These things also help your Nova Scotian garden grow!  

For more information on heavy metal contamination you can read our Community Garden Heavy Metal Contamination Study (2011).

Written by: Garity Chapman

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2 thoughts on “Practicing Safer Soil: Growing in the City

  1. Pingback: How Much?: Deciding On Details and Costs In Your Garden. | Halifax Garden Network

  2. Pingback: Weeds as Friends | Halifax Garden Network

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