Soil Testing

A soil test answers questions that observation cannot. Your soil might look beautiful and be phosphorus-deficient. It might be flagged red on every visual indicator and have nutrient levels that are completely adequate. The visible properties of soil (color, texture, smell) are real and important, but they don’t tell you what’s in there chemically.

What a soil test tells you

A standard soil-test report typically reports:

• pH — the soil’s acidity/alkalinity. Most vegetables prefer 6.0–7.0; blueberries need 4.5–5.5; many ornamentals tolerate wider ranges.
• Organic matter % — by Loss-on-Ignition; reflects the soil’s biological capital. 3–5% is typical for healthy garden soil; >5% is excellent.
• Macronutrients — phosphorus (P), potassium (K), sometimes nitrogen (N, though N moves fast and is harder to test meaningfully)
• Secondary nutrients — calcium (Ca), magnesium (Mg), sulfur (S)
• Micronutrients — iron, manganese, zinc, copper, boron, sometimes molybdenum
• CEC (Cation Exchange Capacity) — the soil’s nutrient-holding capacity; a function of clay and organic matter content
• Base saturation — what percentage of the CEC is occupied by Ca, Mg, K, and other base cations

Most reports also include amendment recommendations based on the crop you specify — e.g., “Lime: 50 lb/1000 sq ft to raise pH to 6.5 for vegetables.”

When to test

• Before starting a new garden, especially on suburban fill, urban soil, or land with unknown history
• Every 3–5 years thereafter as a routine check-in
• When something is going wrong and you don’t know why (chronic poor growth, yellowing across many crops, problems that persist after compost addition)
• Before adding lime, sulfur, or large quantities of any specific amendment — guessing wastes money and can harm the soil

Where to send the sample

• U.S.: most state university Extension services run soil-testing labs. Penn State, Cornell, UMass, Texas A&M, and others. $15–$30 typical price. Look for “[your state] soil test extension.”
• Canada: provincial agriculture ministries and private labs (e.g., A&L Canada Laboratories).
• Elsewhere: national/regional agricultural agencies or private soil labs.

How to take a sample

• Avoid odd spots — don’t sample where a compost pile was, where the dog goes, or right at a bed’s edge
• Composite from 5–10 spots across the area you want to characterize — small scoops mixed in a clean bucket
• Top 6 inches of soil for most garden purposes
• Dry the sample before mailing (some labs want it dry; check instructions)
• Submit cropping history and intended use with the sample — recommendations depend on it

What a soil test does not tell you

• Biological activity — the soil food web doesn’t show up on a standard test (specialized biology assays do exist)
• Heavy metal contamination — lead, arsenic, cadmium require a separate, specialized test (always advisable on urban or post-industrial soil)
• Compaction, drainage, root depth — measured by observation, not chemistry
• Pesticide residues — separate specialized testing

See also

Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.

• Subset of: [[gardening]]
• Shares approach with: [[pH-management]]
• Member of: [[practice]]

Sources

• Cornell University Cooperative Extension, Soil Health Test documentation
• USDA NRCS Soil Health Assessment publications
• Various Extension service soil-testing guides

Rooted in life.