Soil pH is a measure of your soil's acidity (sourness, a measure of below 7.0) or alkalinity (sweetness, a measure higher than 7.0), with 7.0 being neutral. Most garden plants prefer a pH in the neutral range. Some plants are more specific in their requirements. Lilacs and clematis thrive in sweet soils. Rhododendrons and blueberries like a lower pH. You can adjust the pH in different parts of your landscape.
Generally speaking, if your plants are growing healthy and well, your pH is probably fine. If your plants are having nutrient problems or are not growing vigorously, it’s worth it to test your pH. If the soil’s pH is not within an acceptable range for the plants you are growing, the plants will not be able to access the nutrients in the soil, no matter how much you feed them.
You can buy many types of pH testers in a garden center. You can also bring a sample into your local Cooperative Extension office, to be tested for a nominal fee. Once you know what your pH is, you can begin to adjust it slowly. You add some form of lime to raise pH and a form of sulfur to lower it. What type and how much depends upon your soil and test results. Your Extension report and most testing kits will tell you what to do once you get your results.
Adding lime or sulfur to alter soil pH is not a quick fix. It can take months to register a change in the pH and you will need to periodically retest your soil to insure it doesn’t revert to its old pH. It is sometimes easier to simply change your plants to suit your pH.