Soil pH measures the acidity or alkalinity of the soil on a scale from 0 to 14. This chemical property dictates the solubility and availability of essential nutrients, profoundly impacting plant health. When the pH level is too high or too low, nutrients like phosphorus, iron, and zinc can become chemically inaccessible to plant roots. Using pH test strips offers a fast, accessible, and cost-effective way for home gardeners to gauge soil conditions.
Gathering Supplies and Soil Samples
Before testing, gather your soil pH test strips, a clean container, and distilled water. Distilled water is necessary because the minerals and chemicals in tap water can interfere with the test reagents, leading to inaccurate results. You must also collect a representative soil sample from the area you intend to test by collecting small amounts of soil from multiple spots.
To obtain a reliable sample, dig down four to six inches below the surface using a clean trowel, which is the typical depth of the plant’s root zone. Remove large pieces of debris, such as rocks, roots, or plant matter. Combine all the small samples in your container and mix them thoroughly to create a uniform blend.
Performing the Strip Test
Once the soil sample is prepared, create a liquid slurry to expose the pH test strip to the soil’s chemical properties. Place a small amount of homogenized soil into a second clean container. Add distilled water using a specific ratio, such as one part soil to five parts water, to ensure enough liquid for the test.
Stir the mixture vigorously for several seconds, then allow the soil particles to settle to the bottom of the container. This settling time creates a clear liquid layer, called the supernatant, on the surface. Dip the tip of the pH test strip into this clear liquid, making sure not to touch the underlying soil sediment.
The final step is to read the strip according to the manufacturer’s instructions, which typically requires waiting a few seconds up to one minute. Immediately compare the color change on the strip to the color chart provided with the kit. Reading the strip too early or too late can lead to an incorrect result.
Understanding the pH Scale and Results
The pH scale is logarithmic, meaning each whole number change represents a tenfold difference in acidity or alkalinity. A pH reading of 7 is considered neutral, while numbers below 7 indicate increasing acidity, and numbers above 7 signify increasing alkalinity. Most vegetables, grasses, and ornamental plants thrive in a slightly acidic to neutral range, generally between 6.0 and 7.0.
Comparing your strip’s color to the chart in good, natural light yields the final pH number. If the soil is too acidic (below pH 6.0), phosphorus and certain secondary nutrients can become locked up, and elements like aluminum can become toxic. Conversely, if the soil is too alkaline (above pH 7.5), micronutrients such as iron and manganese become less soluble and unavailable.
Correcting Imbalances in Soil pH
After determining your soil’s pH, you can take steps to adjust the balance, though corrections should always be made gradually. If your soil is too acidic, raise the pH by incorporating agricultural lime or dolomite into the top layer. These materials introduce calcium and magnesium carbonates that neutralize the acid over time.
For soil that is too alkaline, the pH can be lowered by applying amendments such as elemental sulfur or aluminum sulfate. Elemental sulfur relies on soil bacteria to convert it into sulfuric acid, which can take several months to achieve a noticeable change. Always follow application rates carefully, as over-correcting the pH can be detrimental to plant health.
Because soil adjustments are a slow chemical process, re-test the soil periodically, such as every six to twelve months, to monitor the change. Incorporating organic matter, like compost, can also help buffer the soil, making it more resistant to drastic pH fluctuations.