Soil pH is a measure of hydrogen ion concentration. The scale runs from 0 to 14; below 7.0 is acidic, 7.0 is neutral, and above 7.0 is alkaline. Because the scale is logarithmic, a soil at pH 5.0 is ten times more acidic than one at pH 6.0. This non-linear quality is why even small pH changes have large effects on soil chemistry.
Why pH Matters More Than Fertilizer Amount
Nutrients in soil exist in different chemical forms. Whether a plant root can absorb a nutrient depends on whether it is in a soluble, plant-available form — and pH determines that. The classic example is phosphorus: in neutral-to-slightly-acidic soil, phosphorus exists as H₂PO₄⁻, which is readily absorbed by roots. As pH climbs above 7.5, phosphorus reacts with calcium to form calcium phosphate compounds that are nearly insoluble. A soil test might show high total phosphorus, but the plant has no access to it.
Iron and manganese show the opposite problem: they become increasingly soluble and potentially toxic as pH drops below 5.5. Boron availability peaks between 6.0 and 7.0 and drops sharply outside that range. Molybdenum — required in trace amounts for nitrogen fixation in legumes — is only available in alkaline conditions and becomes deficient in acidic soils.
Canadian Soil pH by Region
Regional patterns in Canadian soil pH reflect geology, rainfall, and land use history:
- Atlantic Canada (Nova Scotia, New Brunswick, PEI): Naturally acidic soils, often pH 5.0–6.0. Granite-based geology and high rainfall leach basic cations. Liming is routine for agriculture and home gardens.
- Quebec and Ontario: Variable, ranging from 5.5 in forest soils to 7.5 in limestone-influenced areas of the Niagara Escarpment and eastern Ontario. Urban soils can be highly alkaline near concrete structures due to lime leaching.
- Prairie Provinces: Saskatchewan and Alberta soils commonly range from 6.5 to 8.0. Many prairie soils contain free calcium carbonate, which buffers pH and makes acidification difficult. Saline-sodic soils in the Peace River region can reach pH 8.5 or higher.
- British Columbia: Coastal areas tend toward acidity (5.5–6.5); interior valley soils, particularly in the Okanagan, are typically neutral to slightly alkaline (6.5–7.5) and support commercial fruit production.
pH Ranges for Common Canadian Crops
These ranges represent the pH at which each plant group performs well in Canadian conditions. Soils significantly outside these ranges typically show reduced growth, poor colouring, or specific deficiency symptoms even when fertility is otherwise adequate.
Vegetables
- Tomatoes, peppers, eggplant: 6.0–6.8
- Leafy greens (lettuce, spinach, kale): 6.0–7.0
- Root vegetables (carrots, beets, parsnips): 6.0–7.0
- Potatoes: 5.0–6.0 (lower pH reduces scab disease pressure)
- Brassicas (cabbage, broccoli, cauliflower): 6.5–7.5
- Legumes (beans, peas): 6.0–7.0
- Onions, garlic: 6.0–7.0
- Cucumbers, squash, zucchini: 6.0–7.0
- Corn: 5.8–7.0
Fruit Crops
- Blueberries: 4.5–5.5 (strict; they fail to thrive outside this range)
- Strawberries: 5.5–6.5
- Raspberries, blackberries: 5.5–6.5
- Apples, pears: 6.0–7.0
- Sour cherries: 6.0–7.0
- Grapes: 6.0–7.0
Common Ornamentals
- Rhododendrons, azaleas: 4.5–6.0
- Roses: 6.0–7.0
- Hostas: 6.0–7.5
- Hydrangeas: 5.5–6.5 (pH affects flower colour in H. macrophylla)
- Most lawn grasses: 6.0–7.0
Home pH Testing Methods
Several methods are available at different price points and accuracy levels:
pH Meter (Electronic)
A basic soil pH meter costs $15–$40 at garden centres or online. Accuracy is typically ±0.2 pH units, which is sufficient for garden decision-making. To use: take soil from 5–10 cm depth, mix a small amount with distilled water in a 1:1 ratio, insert the probe into the slurry, and wait 60 seconds for a stable reading. Calibrate the meter with a buffer solution before each use session; pH electrode drift is common and uncalibrated meters give unreliable results.
pH Test Strips
Strips dipped in a soil-water suspension change colour according to pH. They are less precise than meters (±0.5 units) but useful for a quick rough assessment across multiple spots in a garden. They are single-use, inexpensive, and require no calibration.
Laboratory Test
A lab pH reading is the most accurate option. It is conducted on a buffered solution and typically reports to one decimal place with consistent methodology. If precision matters — for example when adjusting for blueberries or potatoes — a lab test is worth the cost. Most Canadian provincial labs include pH in any standard soil panel.
Timing of pH Adjustments
Lime (for raising pH) should be applied in fall wherever possible. Ground calcium carbonate reacts slowly with soil moisture and microbial activity over winter, producing measurable change by the following spring. Spring application works but results may not be fully apparent until the second year. On established lawns, lime must be watered in and cannot be incorporated; reaction is slower than in tilled beds.
Elemental sulfur (for lowering pH) also works slowly — 6 to 12 months for a measurable change under warm, moist conditions. Sulfur should not be applied within 2–3 weeks of seeding or transplanting as high local concentrations can injure roots. For blueberry establishment, acidification should begin 1–2 years before planting.
Re-testing After Amendment
Wait at least 6 months after a lime or sulfur application before re-testing pH. Retesting too soon produces a reading that reflects the raw amendment rather than a stabilized soil response. In practice, a full growing season between application and re-test provides the most useful comparison.
This article focuses on pH. For a complete walkthrough of a soil test report — including CEC, organic matter, and macronutrient figures — see How to Read a Backyard Soil Test Report.