How to Read Your Soil Test Results
Start with pH and the lab's lime recommendation. Aim for pH 6.0 to 7.0 for most vegetables, follow the lab's rate, and ignore nitrogen numbers. Here is wh...
Published by ThriveThyme
soil test soil ph lime fall garden
How to Read Your Soil Test Results
Look at three things first: soil pH, the lime or sulfur recommendation, and the crop you plan to grow. For most vegetables a pH between 6.0 and 7.0 is the goal. If the lab gives a lime rate, follow it. Do not guess.
Enter your pH in the Soil Test Desk to see which of your crops are in range. No lab report yet? Find your state extension soil lab in the Get a real lab test list.
Soil pH
pH measures acidity on a scale of 0 to 14. Seven is neutral, lower is acidic, higher is alkaline. Oklahoma State Extension says most plant nutrients are most available in mildly acidic soil from 6.0 to 7.0. NC State Extension gives the same 6.0 to 7.0 range for most plants.
| Your pH | What it means | Usual next step |
|---|---|---|
| Below 5.5 | Strongly acidic. Many vegetables struggle | Lime at the lab's rate |
| 5.5 to 6.0 | Acidic. Fine for some crops, low for others | Lime if growing crops that want 6.2 or higher |
| 6.0 to 7.0 | The target range for most vegetables | No lime needed |
| Above 7.0 | Alkaline. Iron and other nutrients can get tied up | Do not lime. Use sulfur only if the lab recommends it |
Some crops are the exception. Blueberries want about 4.5 to 5.5. White potatoes prone to scab do best near 5.0 to 5.2. See the best soil pH for vegetables for every crop.
Buffer pH and the Lime Rate
If your pH is low, the lab also measures buffer pH. This shows how strongly the soil resists change, and it is what the lab uses to calculate how much lime you need (Clemson HGIC, Oklahoma State Extension). Sandy soil needs less lime than clay to move the same amount. Use the lab's rate for your bed size. Do not use a generic bag instruction.
Phosphorus, Potassium, Calcium, and Magnesium
These show up as low, medium, or high, or as parts per million. Each lab uses its own scale, so compare your numbers only to that lab's ratings. If a nutrient reads high, skip fertilizer that contains it. If it reads low, the report lists how much to add. Lime also supplies calcium and magnesium (NC State Extension).
Nitrogen
Most routine home garden reports do not give a nitrogen number, because soil nitrogen shifts fast with rain and temperature. Expect a general nitrogen recommendation by crop instead.
Organic Matter and Salts
Organic matter is reported as a percent. Compost and leaf mold raise it slowly over seasons. If you have added a lot of manure or manure compost, ask the lab for a soluble salts reading. Colorado State Extension warns that manure-based compost can be high in salts and says to test before adding more than 1 inch in a season.
Common Mistakes
- Assuming every garden needs lime. NC State says soil pH can be too low or too high, and not to assume you need lime.
- Adding lime on top of a pH that is already in range.
- Treating a home test kit as exact. A kit is fine for a quick check. Use a lab for lime rates.
- Testing right after liming or fertilizing. Wait 6 to 8 weeks.
Next Steps
If lime is recommended, read when and how to add lime to a garden in fall. If your soil is fine, add compost using how to use compost and manure in fall beds.