How to Do a Soil Test?

What You Need to Know

Performing a soil test is straightforward and affordable, yet it provides information that can transform your gardening results. Here is a step-by-step guide to collecting and submitting a soil sample for professional analysis.

Before you begin, gather your supplies. You will need a clean plastic bucket, a trowel, garden spade, or soil probe, and a clean plastic bag or the sample container provided by your testing laboratory. Avoid using galvanized metal buckets or tools, as zinc contamination can skew results.

Step one is to identify your sampling areas. Different parts of your property may have different soil conditions. Test your front lawn separately from your back lawn if they have different grass types or growing conditions. Test vegetable gardens, flower beds, and fruit tree areas separately from lawn areas. Each distinct area needs its own composite sample.

Step two is to collect subsamples. For each area, take soil cores from 10 to 15 randomly distributed spots. This is important because soil nutrients can vary significantly across even a small area. A single sample from one spot is unreliable. Walk a zigzag pattern across the area, stopping periodically to collect a core.

For lawns, push your tool straight down to a depth of 4 to 6 inches, remove the core, and drop it into your bucket. For vegetable gardens and flower beds, sample to a depth of 6 to 8 inches, which represents the typical root zone depth for these plants.

Avoid sampling from unusual spots like edges of driveways, areas near downspouts, compost piles, pet areas, or spots where fertilizer has recently been spilled. These locations do not represent your overall soil condition.

Step three is to prepare the composite sample. Mix all the subsamples thoroughly in the bucket, breaking up any clumps. Remove stones, roots, grass, and other debris. Spread the soil on clean newspaper or plastic and allow it to air dry if it is very wet. Do not use an oven or microwave to dry soil, as heat can alter nutrient availability.

Step four is to package the sample. Fill the sample bag or container with approximately one pint or two cups of your mixed, dried soil. Label the sample clearly with your name, the date, and a description of the area (such as front lawn, vegetable garden, or rose bed). Include information about what you are growing or plan to grow, as this affects the fertilizer recommendations.

Step five is to submit the sample. The most reliable and affordable option is your state university cooperative extension service. Most charge between 10 and 30 dollars per sample and return results with detailed, region-specific fertilizer recommendations. University labs use standardized testing methods calibrated for your area's soil types.

Private laboratories and mail-in services like Soil Savvy or MySoil are also available, often at higher cost. Home testing kits sold at garden centers provide rough pH and nutrient estimates but lack the accuracy and detailed recommendations of professional lab analysis.

Step six is to interpret the results. Your report will typically include soil pH, buffer pH (used to determine lime requirements), organic matter percentage, and nutrient levels for phosphorus, potassium, calcium, magnesium, and sometimes micronutrients. Each nutrient will be rated as low, medium, optimal, or high.

The accompanying recommendations will specify exactly how much lime, sulfur, or fertilizer to apply, often in pounds per 1,000 square feet or per 100 square feet. Follow these recommendations rather than the generic instructions on fertilizer bags.

Timing matters. The best time to test is late summer or fall for lawns, as this allows time to apply lime or sulfur amendments that need months to take effect before the next growing season. For gardens, test in late fall or very early spring. Avoid testing within six to eight weeks of a fertilizer or lime application, as recent amendments will skew results.

Retest every two to three years to monitor changes and adjust your fertilization program accordingly.