Soil pH – What is it and what does it mean?

farmland-801817_960_720Soil pH or soil reaction indicates the acidity or alkalinity of soil. It’s measured in pH units. pH units run on a scale of 0 to 14. As numbers decrease from 7, the acidity level gets higher. As numbers increase from 7, the alkalinity is higher. Soils generally range from the extremely acidic pH of 3 to a very alkaline pH of 10. This range is a result of many factors, including a soil’s makeup and the amount of yearly rainfall an area receives. Slightly acid soils with a pH of 6 – 6.5 provide the most favorable environment for nutrient availability. Most trees perform well in these soils.

So what does pH do?

Soil pH has an indirect and far-reaching effect on trees. Nutrients become available or unavailable according to the soil’s pH level. As mentioned earlier, a slightly acidic soil affords plants and trees with good access to all nutrients so they’ll grow well and get the nutrition they need from the soil. Unfortunately, if your soil is too low or too high in pH, you can have problems with your trees and plants. They can even become poisoned depending upon what nutrients they receive. Soil pH influences soil-dwelling organisms whose well-being affects soil conditions and plant health. Slightly acidic conditions are also what earthworms like as well as microorganisms that convert nitrogen into forms that trees can use.

How do you measure soil pH?

Soil pH provides various clues about soil properties and is easily determined. The most accurate way to figure it out is a pH meter. You can also use certain dyes, but they’re less accurate. Many dyes will change color with an increase or decrease of pH making it possible to estimate the soil. This method is probably accurate enough for you to use. You put the sample dye on the soil in question for a few minutes and the color it changes to determines what your soil pH is. The kits include color charts and are located in many garden stores.  To determine your soil’s overall pH, you should take several samples from different parts of the yard. Soil pH can vary from different areas.

How do you adjust your soil pH?

You should know your soil’s texture as well as its pH before attempting to change it. Is it clay, sand or something in-between? In Central Texas, it will probably be clay. (See our blog post on Austin’s soils for more information.) Lime is usually added to acid soils to increase soil pH. The addition of lime not only replaces hydrogen ions and raises soil pH, thereby eliminating most major problems associated with acid soils but it also adds two nutrients, calcium and magnesium to the soil. Lime can also make phosphorous which makes nitrogen more available. Nitrogen hastens the decomposition of organic matter. Liming materials are relatively cheap and leave no objectionable residues in the soil.

Sulfur is added to soil to decrease pH. Sulfur can be bought in a powder or a pellet. It can be spread fairly uniformly and doesn’t damage the soil. Elemental sulfur can take several months to change the soil’s pH because the soil bacteria need to change it sulfuric acid. Other forms of sulfur can be quicker. You will need to determine which to use based on your soil’s needs.

Neither lime nor sulfur is soluble in water, so it’s wise to mix these materials thoroughly into the top 6 inches of soil when quick action is needed. Otherwise, just lay the material on top of the ground and let it gradually work its way down.

We hope this answers your questions about soil pH and doesn’t create more questions for you. We do not test or manipulate soil at Austin Tree Service. However, you can go to your local garden store if you’re concerned. They will be happy to help you.  If you notice any tree problems, please feel free to call us at 512-341-8888. Thanks.