Soil Test Translator: What Your Soil Test Results Mean
Type in the numbers from a University of Delaware or Penn State soil test report and get a plain-English explanation: which nutrients are low, optimum or high, what your pH means for a lawn or vegetable garden, and how each lab says to apply lime. Follow your lab’s own recommendations; this tool explains them.
How each lab rates your numbers
University of Delaware uses the Mehlich-3 test and reports phosphorus, potassium, calcium and magnesium as Fertility Index Values: Low 0-25, Medium 26-50, Optimum 51-100, Excessive over 100 (UD). UD: “Cool- and warm-season lawn grasses grow best in a pH range between 6.0 and 7.0. The best pH range for vegetable and flower gardens is 5.8 to 6.3.” (UD soil pH guide)
Penn State also uses Mehlich 3 and reports “parts per million (ppm) elemental P, K, and Mg” (Penn State). For a home lawn, optimum soil test phosphorus is 45-75 ppm and potassium is 180-220 ppm, and the pH goal is 6.5 for most grasses or 6.0 for fine fescues and bentgrass (crop code 2001).
What we don’t rate: we found no published UD or Penn State range for rating organic matter on home samples, and no Penn State optimum ranges for lawn magnesium and calcium. For those, the tool shows your number and points you to the rating bar on your report. Penn State’s home garden report sheet isn’t published online, so for Penn State vegetable garden reports the tool shows Penn State general guidance for vegetables beside your number as a reference, not a rating: pH 6.0-7.0, organic matter 3.0-5.0%, and Mehlich 3 P 35-100, K 100-200, Ca 1000-2000 and Mg 50-200 ppm (Penn State Guide to Urban Soil Management, Table 4).
Frequently asked questions
How do I read my soil test results?
Find three things on the report: the pH, the nutrient levels and the recommendations. Penn State reports phosphorus, potassium and magnesium in parts per million (ppm) on a bar marked Below Optimum, Optimum and Above Optimum. The University of Delaware reports phosphorus, potassium, calcium and magnesium as Fertility Index Values (FIV) rated Low, Medium, Optimum or Excessive. Then apply the rates in the recommendations section.
What do the ratings on a soil test mean?
UD: Low (0-25 FIV) will very likely limit plant growth; Medium (26-50) should be increased into the optimum range; Optimum (51-100) means nutrient additions are rarely recommended; Excessive (over 100) means additions are not recommended. Penn State: Below Optimum means the nutrient is deficient, Optimum means it is adequate, and Above Optimum means it is more than adequate.
What should my soil pH be for a lawn or vegetable garden?
The University of Delaware says lawn grasses grow best between pH 6.0 and 7.0, and the best range for vegetable and flower gardens is 5.8 to 6.3. Penn State’s home lawn pH goal is 6.5 for most grasses and 6.0 for fine fescues and bentgrass.
How much lime should I add?
Use the lime rate on your lab report. Labs calculate it from a buffer test, which UD notes is not available in home soil test kits. Split large rates: UD says to split rates over 100 lb per 1000 square feet into 40-50 lb applications about 3-4 months apart, and Penn State says to split lawn rates over 100 lb per 1000 square feet into 2 or more applications 4 to 6 months apart.
Why doesn’t my soil test show nitrogen?
Penn State says there is no reliable test for evaluating the amount of nitrogen in soils that is available to crops over the growing season, so nitrogen recommendations are based on what the plants need each year.
What’s the difference between ppm and FIV?
Penn State reports nutrients in ppm; to convert ppm to pounds per acre, it says to multiply by 2. UD reports P, K, Ca and Mg as Fertility Index Values. For phosphorus, UD gives 100 FIV as equivalent to 100 ppm or 200 lb per acre of Mehlich-3 phosphorus.
Related: organic fertilizer and N-P-K, when to stop mowing in fall, is it too late to plant grass seed, and the planting calendar by ZIP.
Sources
- University of Delaware: Delaware Gardener’s Guide to Soil pH; Interpreting Soil Phosphorus and Potassium Tests; Soil Testing Program: Nutrient Recommendations; Soil Testing Program: General Information
- Penn State Agricultural Analytical Services Lab: Home Lawn to Maintain, Crop Code 2001 (PDF); Understanding your report: Home Lawn; Understanding your report: Home Garden; Understanding your report: Agronomic Crops; Soil Fertility Testing; Submission form: turf, home garden and landscape (PDF)
- Penn State College of Agricultural Sciences: Guide to Urban Soil Management: Key Parameters Assessed in Soil Testing