Fall Soil Testing in Ontario: How to Sample Your Yard Before Spring
Fall is one of the best times to test your soil in Ontario. For a lawn, take at least 15 small cores 10 to 15 cm deep in a W or M pattern, mix them in a clean bucket and send a sample to an accredited lab. Results for pH, phosphorus, potassium and magnesium come back in time to plan lime, fertilizer, topsoil or sod work for spring, and London even has an accredited lab, A & L Canada Laboratories, right in the city.
A soil test costs far less than a season of guesswork. Here is how to do it properly.
Why Test Your Soil in the Fall?
The Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) recommends sampling at the same time each year and notes that fall sampling suits ground that will be seeded in spring. For homeowners, fall testing has a few practical advantages:
Time to plan. Lab results arrive over the winter, so you can order the right topsoil, lime or fertilizer before the spring rush.
Better decisions on new lawns. If you are planning sod or seed in spring, you will know whether the existing soil can be improved or should be replaced.
Diagnose problem areas. Patches that stayed thin or yellow all summer may have a pH, nutrient or salt problem rather than a watering problem.
Ground is easy to sample. Before freeze-up, the soil is moist and easy to core.
What a Soil Test Measures
OMAFA's guidance on soil testing for turf explains that a standard turf test always includes:
pH, which controls how available nutrients are to grass roots
Phosphorus (P)
Potassium (K)
Magnesium (Mg)
Labs can add tests for manganese, zinc and organic matter for an extra fee. When the pH is low, labs typically run a buffer pH test, which is used to work out how much lime is needed. One important note from OMAFA: an organic matter test does not tell you how much nitrogen to apply, so nitrogen recommendations are based on the type of turf and how it is used.
Some lawn and garden packages go further. The University of Guelph's Agriculture and Food Laboratory lawn and garden test, for example, includes pH (with buffer pH when pH is below 6.1), calcium, phosphorus, potassium, magnesium, sodium, total salts and organic matter, with recommendations.
How to Take a Lawn Soil Sample
Follow OMAFA's turf sampling steps:
Divide the yard. Areas managed differently, such as the front lawn, back lawn and vegetable garden, should be separate samples. Problem patches should be sampled separately too.
Use a clean tool. A soil probe is ideal, but a clean trowel or spade works. Avoid galvanized or brass tools that can contaminate the sample.
Collect at least 15 cores per area, walking in a W or M pattern so you cover the whole area.
Go 10 to 15 cm deep for residential lawns.
Remove the thatch and grass from the top of each core.
Mix the cores in a clean plastic bucket.
Bag the sample. Most labs need a few hundred grams; the University of Guelph lab asks for about 300 g in a new plastic bag.
Label it and fill in the lab's form, noting what you are growing.
OMAFA suggests repeating lawn tests every 2 to 3 years.
Common Sampling Mistakes
A soil test is only as good as the sample. Avoid these errors:
Taking one big scoop. A single spot can be very different from the rest of the yard. Many small cores give a true average.
Mixing very different areas. Combining a shady front lawn with a sunny vegetable garden produces a result that fits neither.
Sampling right after fertilizing or liming. Wait several weeks so recent applications do not skew the results.
Including thatch, roots or stones. Strip them off so the lab tests soil, not debris.
Sampling too shallow or too deep. Stick to the 10 to 15 cm depth OMAFA recommends for lawns.
Using a dirty bucket. Residue from fertilizer, salt or cleaning products can contaminate the sample.
Where to Send Your Sample in Ontario
OMAFA keeps a list of accredited soil testing labs, last updated in March 2026. Accredited Ontario labs include:
A & L Canada Laboratories Inc., 2136 Jetstream Road, London (519-457-2575)
University of Guelph Agriculture and Food Laboratory, Guelph
SGS, Guelph
Stratford Agri-Analysis, Stratford
Honeyland Ag Services, Ailsa Craig
Activation Laboratories, Ancaster
Eurofins, Ottawa
The province notes that the list is not an endorsement. Call the lab first to ask about homeowner packages and pricing. For reference, the University of Guelph lab lists its lawn and garden test at $90.90 per sample from May 2026 to April 2027, with a turnaround of about 20 business days.
How to Read Your Results
Most reports show your value, a rating (low, medium, high) and a recommendation. Focus on these:
pH: What it tells you: Whether nutrients are available to roots; What to do: Follow the lab's lime or sulphur advice
Buffer pH: What it tells you: How much lime is needed when pH is low; What to do: Apply lime at the recommended rate
Phosphorus and potassium: What it tells you: Whether fertilizer needs extra P or K; What to do: Choose a fertilizer blend to match
Organic matter: What it tells you: How much humus the soil holds; What to do: Topdress with compost or quality topsoil if low
Salts and sodium: What it tells you: Possible road salt or de-icer damage; What to do: Improve drainage, reduce salt use
If salt levels are high along a driveway or road edge, our article on de-icing salt damage explains how to limit the harm.
When to Amend and When to Replace
A soil test helps you decide between improving what you have and bringing in new soil:
Minor nutrient shortfalls: Fertilize based on the report.
pH out of range: Apply lime or sulphur as recommended, then retest.
Low organic matter or a thin layer of soil: Topdress with screened topsoil or compost, or add a new layer before seeding.
Compacted subsoil, construction fill or very poor soil: Strip and replace with good topsoil before laying sod.
What good topsoil looks like
There is no single provincial standard homeowners can point to, but municipal specifications give a useful benchmark. The City of Windsor's topsoil specification, for example, calls for a screened fertile loam with at least 3.0% organic matter, a pH between 5.5 and 7.8 and no stones larger than 25 mm. When you order bulk topsoil, ask whether it is screened and what it is made from.
Our guide to how much topsoil, mulch or gravel you need will help you size the order, and our material calculators do the math for you.
Soil Testing on New Builds
New homes around London often end up with a thin layer of soil spread over compacted subsoil or construction fill. That is one reason new lawns struggle. If you have just moved into a new build, a fall soil test is a smart first step. Sample the front and back separately, and dig a small test hole to see how deep the topsoil actually is. If you find only a few centimetres of soil over hard clay or rubble, adding a proper depth of screened topsoil before laying sod will save years of frustration.
Fall Soil Testing Checklist
Map out separate sampling areas.
Gather a clean bucket, trowel or probe and new bags.
Take 15 or more cores per area at 10 to 15 cm deep.
Remove thatch, mix well, bag and label.
Ship the sample with the lab's form before the ground freezes.
Plan spring lime, fertilizer, topsoil or sod based on the results.
FAQ
When is the best time to test soil in Ontario?
Late summer and fall work well. OMAFA recommends sampling at the same time each year and notes fall sampling suits ground that will be seeded in spring.
How deep should I sample my lawn?
OMAFA recommends sampling residential lawns 10 to 15 cm deep, with at least 15 cores per area mixed into one sample.
Where can I get my soil tested near London, Ontario?
A & L Canada Laboratories on Jetstream Road in London is on OMAFA's list of accredited soil testing labs. Other accredited labs include the University of Guelph's Agriculture and Food Laboratory and labs in Stratford and Ailsa Craig.
What does a lawn soil test include?
A standard turf test measures pH, phosphorus, potassium and magnesium. Labs may add buffer pH, organic matter, micronutrients, sodium and salts.
How often should I test my lawn soil?
OMAFA suggests every 2 to 3 years, or sooner if you are planning major work such as new sod.
Need Topsoil or a New Lawn?
SPM Landscape & Excavation has supplied topsoil and installed sod across London since 2006. We are WSIB covered with $1 million in liability insurance. Call (519) 474-0008 or email spmlandscape@gmail.com for a free quote.
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