Garden Soil pH Testing and Amending
Soil pH Section Overview:
pH stands for potential hydrogen, and it can tell you a lot about your soil. For your purposes think of it as potential nutrients—pH determines which nutrients are available to plants. In fact, pH affects the microorganism activity in your soil. Soil pH determines its acidity (sourness) or alkalinity (sweetness). The lower the pH, the more acidic your soil is; the higher the pH the more alkaline it is. A pH of 7 is neutral (neither acidic or alkaline). For gardening, most plants prefer a soil pH between 6 and 7 with 6.5 being your target soil pH. Some plants prefer more acidic (below a pH of 6) or alkaline soils (above a pH of 8), but for general gardening, all that matters is that your soil not be too acidic or alkaline unless the plants you select can tolerate these conditions. Plants are very flexible with respect to pH, so long as your site isn’t near the extremes of acidity or alkalinity for the particular plants.
If your soil pH is too extreme for your plants, it creates an unhealthy environment by limiting the nourishment that is available to the plants and by weakening their natural defenses against pestilence and disease.
Soil pH Test
The pH test is a simple indicator test requiring some soil, water (use distilled water for best results), a clean cup or jar, and a Garden Tutor pH test strip. The Garden Tutor pH test strips cover a pH range of 3.5 to 9.0 in .5 increments. Each pH test strip has four pads that change color depending on the pH of the test material. Each pad on the pH test strip covers a specific segment of the pH range. Having four pads helps with accuracy since a pH range of 3.5-9 is broad and the color changes can be subtle and difficult to determine.
Garden Tutor pH test
Adjusting Soil pH
Before you can adjust your soil pH you should know your soil type (Sand, Silt, Clay or Loam). Your soil type can affect the quantity of pH amendment (lime or sulfur) you use. This due to the “buffer capacity” of the soil which is a measure of how well soil can resist changes in pH. For example, clay soils have a high buffer capacity and require more lime than other soil types to alter pH. Clay soils require more work to alter pH but once you change them the effects will last longer so you don’t need to add lime as frequently. You should also be aware that it takes a lot of amendments to change pH. If you need a more acidic soil you can use sulfur or naturally acidic organic materials (peat moss, leaves or needles from acidic plants). If you use organic material the pH change will be very gradual; if you are in a hurry you may opt for sulfur. It is best not to use commercial plant acidifiers containing aluminum sulfates or fertilizers containing ammonia to alter soil pH; they are best used only to maintain plants already growing in acidic soil, and misuse can ruin your soil.
The best way to raise soil pH is to add lime. Lime is readily available and easy to apply. You may have a few types of lime to choose from depending on what retailers in your area carry. Pulverized or pelletized limestone is usually a good choice (pelletized lime can be used in a broadcast spreader). Dolomitic limestone is limestone which contains magnesium and a few other trace nutrients. You can use ground limestone, just be aware that it is a powder, and powders are harder to apply with a broadcast spreader. Hydrated limes are also available; they work quickly but can burn plants and flesh if used incorrectly. In any case, be sure to follow the application rates and package instructions strictly. If you add too much at one time you can harm your plants and your soil.
Below is a handy soil pH adjustment calculator that you can use to determine how much lime or sulfur is needed to raise or lower your soil pH. Just note if the amounts of lime or sulfur from our calculator disagrees with the label on the product you buy, always go with the manufacturer guidelines. Adjusting soil pH with lime and sulfur is not permanent so you’ll need to recheck soil pH every year or two and make adjustments as necessary. The degree and duration of the change depends on how finely ground the amendments are (lime and sulfur). The more finely ground (e.g. pulverized) the faster they alter pH but shorter their effects last (generally 1-2 years depending on your climate). Note that pelletized lime is finely ground but aggregated with a binding agent to form easy to spread pellets. It is best to apply lime and sulfur in the fall or early spring, so they can start working on your soil before you plant.
Additional pH Test Support:
Due to the variable content of minerals and salts found in soils, sometimes one or two of the color pads can be slightly misaligned with the color chart. If you have a pad that seems to have a color that is out of sync you can accurately determine your soil pH using our guidance below. If you still have questions or need help interpreting your results send a picture of your result to email@example.com, we are glad to help!
Before you begin, make sure to have followed the detailed instructions in the Garden Tutor Soil pH Testing Handbook. Make sure you are following the guidance below as these are common reasons people get mixed results:
1) Garden Tutor pH test strips are specially calibrated for testing soil ONLY (specifically a slurry made of equal parts soil and distilled water). They are not designed to test the pH of urine, saliva, water, pools/spas, or any other liquids such as cleaners, acids, foods, beverages, and soaps, caustics. You will NOT get accurate test results if you use these pH test strips to test anything except soil.
2) It is best to use distilled water for making your soil water slurry. Using distilled water is not required but excessively “hard” or “soft” water negatively can impact the pH test strip results.
3) After you make your soil water slurry, let the mixture sit for a minimum of 20 minutes. For best results let the mixture sit for a few hours before testing. Then mix it one more time just before testing.
4) Make sure you wait one minute after briefly dipping the pH test strip into the soil/water solution. This is the optimal time to compare the pH strip to the color chart.
5) Make sure you are viewing the color chart and pH strip in a well-lit room. Ideally, by a sun-filled window.
6) Used pH test strips that are 3-4 minutes old will start to fade and should be discarded.
7) Always reseal the container after removing a strip for testing. Unused test strips exposed to excess moisture for extended periods can react with the moisture and fail to function when used.
8) Due to variations in printing color and soil minerals, the color chart can appear a bit off from the actual colors of the pads on the test strips. You are looking for the best overall match based on all 4 color pads. If one pad seems off try to find the best overall column and that will be your soil pH. Use the Troubleshooting chart included with your pH booklet.
Garden Tutor pH Test Strips Examples