When and how
Test before you fertilize heavily, when plants look consistently poor, or every 2–3 years for a vegetable bed. Take 10–15 small samples from the top 6 inches across the bed, mix them, and send the composite sample — one handful from one corner tells you almost nothing.
What the numbers mean
pH tells you nutrient availability, not fertility itself. Organic matter tells you about soil structure and water holding. Nutrient numbers only matter against your crop and your soil type — a number that is low for one crop can be fine for another. Follow the lab's recommendation, not a generic online chart, and retest after amending.
How to take a good sample
A soil test is only as good as the sample. Walk the bed in a zigzag, taking 10–15 small samples from the top 6 inches, avoiding paths, compost heaps and recently fertilized spots. Mix them in a clean bucket, remove stones and roots, and send the composite sample as the lab instructs. Test vegetable beds and lawns separately — they are managed differently and their results will differ. Label each sample clearly with the bed name and date.
Reading the results
pH is usually the first number to look at: most vegetables prefer slightly acidic to neutral soil, roughly pH 6.0–7.0, but some crops, like blueberries, need much more acidic soil. Organic matter percentage tells you about soil structure and water-holding capacity — below 3% is low for a vegetable bed, above 5% is good. Nutrient numbers (phosphorus, potassium, magnesium, calcium) only mean something against the lab's own reference ranges, which vary by soil type and region, so use the lab's interpretation, not a generic online table.
What to do with the results
Follow the lab's lime recommendation for pH before adding fertilizer — pH affects nutrient availability more than the amount of fertilizer you add. Add compost for low organic matter, regardless of nutrient numbers, because it improves structure as well as fertility. If one nutrient is high, do not add more of it: excess phosphorus, for example, is common in gardens that have been fertilized with balanced fertilizer for years, and adding more wastes money and can harm soil life. Retest after 2–3 years to see whether your amendments worked.
Frequently asked questions
Are home test kits accurate?
Home kits give a rough pH and sometimes a rough nutrient indication, but they are less accurate than a lab test and do not measure organic matter. Use a kit for a quick check, a lab for decisions that cost money, like liming or fertilizing a large area.
When should I test?
Autumn is convenient, because results arrive in time to amend soil before spring planting. Avoid testing straight after fertilizing or liming, which skews results.