Soil pH Section Overview:
Soil pH — Background on soil pH and why it matters for gardening
Soil pH Test — How to test your soil using the Garden Tutor Soil pH Test Strips
Adjusting Soil pH — How to alter your soil pH (raise or lower it) using various amendments (Typically lime of sulfur)
A few general facts about soil pH — Somewhat generalized information that relates to soil pH
Additional pH Test Support — A handy troubleshooting guide and examples of pH tests to help you interpret your results. (SCROLL TO BOTTOM OF PAGE)
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.
The pH strips have been specifically designed and calibrated for soil testing and cover a pH range that encompasses nearly all garden soils. If you follow the subsequent steps you should be able to determine your soil pH within a .5 increment. If you need pinpoint accuracy, consider sending a soil sample to a professional soil testing laboratory. You can go to the “Toolbox” area of the Garden Tutor site under “Soil Testing” to learn about current options for laboratory soil testing.
- You will need a representative sample of your garden soil. Using a garden trowel or spade, dig a small hole (about 6 inches deep) in your site. Slice a sample from the edge of the hole as if you were cutting a thin slice of cake: cut a sliver from top to bottom, using your hand to hold the slice in your trowel or spade. Remove any stones, grass, etc., and put this sample in a bucket or large container. Repeat this process a few times around your garden site. Mix the soil samples thoroughly in the bucket or container and eliminate any foreign debris.
- Using a tablespoon put 8 level tablespoons (4 ounces/60 ml) of the mixed soil into a clean plastic cup or jar and thoroughly mix with 8 level tablespoons (4 ounces/60 ml) of water for 30 seconds. For best results, let the solution sit for 20 minutes before testing.
- Briefly mix solution one more time and wait 10 seconds for the soil to settle a bit and then dip one pH test strip into the solution. Hold the strip in the solution for 3 seconds.
- Remove the pH test strip and shake it vigorously to remove any dirt on the pads and wait one minute for the soil solution to fully react with the pH test strip. If the pads are still obscured by the dirt after you waited the full minute you can quickly dip the pH strip into a cup of distilled water to rinse off excess dirt. Depending on soil pH some or all the color pads will change color. Match the resulting color(s) with the color chart that accompanied the pH test strips to determine your soil pH. This takes a bit of work and it helps to do this in a well-lit room or by a sunny window to accurately assess the color change against the color chart. Keep in mind, after 5 minutes the pads on the pH test strip will dry out and the colors will fade so the pH test strips will no longer be useful and should be discarded.
Note: If you find that dirt is still making it difficult to see the color pads on the pH test strip you can use a disposable coffee filter to filter your soil/water mixture. Simply place the coffee filter over a small cup and slowly pour your soil/water mixture into the coffee filter. Once enough filtered water has accumulated in the bottom of the cup you can remove the coffee filter and repeat the pH test in this filtered water.
For more consistent results, you can purchase distilled water for the test (it is best to purchase the distilled water just prior to testing as it will have a near-neutral pH when unopened).
We have included enough indicator strips for 100 tests, so you may want to test various parts of your site individually to see if there are variations within your garden. Spring and fall tests are useful, too.
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. 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.
The following charts will give you approximate application rates for lime or sulfur (at rates of lbs/kg per 100 sq. ft/9.3 m2 and lbs/kg per 1000 sq. ft/93 m2). Just note if the chart 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.
A few general facts about soil pH:
- Clay soils tend to be acidic.
- Sandy soils tend to be alkaline.
- Keeping pH at the proper level for the plants in your garden will help reduce garden pests and diseases.
- Lime helps improve the structure of the soil.
- Rather than trying to alter your soil pH with lime or sulfur, using plants suited to your soil pH can save you time, effort and money.
Additional pH Test Support:
If you are having trouble interpreting your results or your color pads do not seem to align with any option on the chart, we have developed a chart to help you determine your soil pH within a 1 pH increment. Due to the variable content of minerals and salts found in soils, occasionally 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 with interpreting your results. Please contact us and send us a picture of your result, we are glad to help!
Before you begin, make sure to have followed the detailed instructions in the Garden Tutor Soil pH Testing Handbook. Also, be sure you are adhering to the following guidance as these are often the 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, 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) Use distilled water for making your soil water slurry.
3) After you make your soil water slurry, let the mixture sit for 20 minutes before testing and remix the slurry one last time just before testing.
4) Make sure you wait one minute after briefly dipping the pH test strip into the soil/water solution. That 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 or more 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.
Examples of pH readings using the Garden Tutor pH Test Strips
Soilless mix pH testing Example:
Examples of low pH (Acidic soils)