Learning Center

Soil pH. Why does it matter?

Let’s just dive right in; soil pH should matter to all of us because it matters to plants.  Many plants, from trees to shrubs, from perennials to turfgrasses, have pH preferences so strong, they might as well be called requirements.  Ignoring plant needs such as soil pH could mean plant decline, all the way up to and including plant death.  Yikes!  Keep reading for details, including ideal pH ranges for commonly used landscape plants.

Let’s start at the beginning; soil pH is the measure of soil acidity or alkalinity.  The scale stars at 0 and goes up to 14, with neutral soils being 7; values less than 7 are acidic and over 7 are alkaline.  Nutrients essential to plant growth are most available in the 5.8 to 6.5 pH range.  Lime can be used to adjust soil acidity, which will increase nutrient availability.  Data suggests that up to 50% of Arkansas soils are below the optimum range.  Soil pH tends to be acidic in areas that used to be heavily forested so new housing developments greatly benefit from soil testing.  Soil pH also effects beneficial soil dwelling organisms such as earthworms, which like slightly acidic soils.

Here is your science quiz for the day: do you know what soil pH stand for and why the ‘p’ is lower case and the ‘H’ is upper case?  It’s because Hydrogen is involved, and elements on the periodic chart are always capitalized!  pH stand for potenz Hydrogen, which basically means the potential to be Hydrogen.  The pH of the soil is indicated by the activity of Hydrogen ions in a solution. Acidic solutions have a high concentration, while alkaline solutions have a lower one.  Mineral nutrients are absorbed by plant roots when the nutrients are dissolved in water.  If the soil is too acidic or too alkaline, some nutrients (such as Nitrogen and Iron) do not dissolve as they should, and are therefore not available to be absorbed by plant roots.

What does all this jargon mean?  If you only get one thing out of this post, this is the take away:  you can feed your plants regularly, with the best high end fertilizers available… and still be starving them if the pH is off.   Yes, YIKES, again!

So, what is the pH of your soil?  There are several ways to test your soil.  If you have never tested it before, we suggest getting a complete soil test done with the University of Arkansas Cooperative Extension Service.  To do this, you will need to get a sample of soil from several different areas of your landscape, remove any plant debris, mix samples in together, allow the soil to dry completely, then take a pint of soil to your county extension office.  This service is free to Arkansas residents and very valuable as it will test soil pH and provide recommendations on how to address pH issues and fertilizer needs.  To accurately test areas with different uses, keep samples separate.  For example, a homeowner with a vegetable garden, a lawn area and landscape beds with shrubs would need to collect three separate collections of samples and provide 3 pints of soil, communicating the use of each when turning in the sample.  The samples are then sent off to a lab and your results will be sent to you.  For complete information on this process, follow this link.

If you have done this soil test in the past and are checking in on the levels for further adjustments, we have inexpensive and easy to use test kits here at The Good Earth.  This test can be done at home and each kit comes with 10 tests each for pH, Nitrogen, Phosphorus and Potassium.  This test also includes pH preferences for over 450 plants as well as complete instructions for adjusting soil conditions.  Testing both spring and fall is recommended.  Samples should be collected the same way as in the above description, with several samples being mixed together to get an accurate average.

Lime is typically used to raise pH (reduce acidity) while sulfur is used to lower it (reduce alkalinity).  Since Arkansas soils tend to be acidic, lime is the most commonly recommended action to address our soil pH issues.  The best times of year to lime are spring and fall.  It’s not recommended to apply more than 50 pounds of lime per 1,000 square feet at one time.  If your soil sample results indicate that between 50 and 100 pounds of lime are needed per 1,000 square feet, apply half in the fall and half in the spring.  If over 100 pounds is recommended, apply no more than 50 pounds per application each spring and fall, until the recommended amount has been applied, testing throughout the process.  It may take several months for an application of lime to effectively change pH.  Certain fertilizers, rainfall and other factors can shift soil pH, making regular testing necessary.

Lime is available in two main forms; pelletized and pulverized.  Pulverized is very fine in texture, and is best applied with a drop spreader.  Pelletized lime is what you would think; pellets of lime.  This form can be easily spread with either a drop or rotary spreader.

Turfgrasses vary in soil pH preferences.  Zoysiagrass, bermudagrass and tall fescue do best in the 5.8 to 7.0 range.  St. Augustingegrass prefers more alkaline soils, in the 6.5 to 7.5 pH range.  Centipedegrass prefers more acidic soil, in the 5.0 to 6.0 range.

Azaleas prefer a 4.5 to 5.5 as do Hollies, Boxwoods 6.0 to 7.5, Gardenias 4.5 to 5.5.  Roses 5.5 to 7.0. pH can also change or intensify bloom color such as in Hydrangeas.  The Farmer’s Almanac also offers this list.

We hope this encourages you to perform a soil test soon!