Soil pH is important to understand if you want your plants to grow well. It can affect the absorption of certain nutrients regardless of whether there are enough of these nutrients in the ground. If a plant can’t absorb needed nutrients, it will die. This leads to irate customers. Soil pH really is important, and it doesn’t have to be hard to understand.
What Is Soil pH?
Simply put, soil pH is the measure of how acid or alkaline your soil is. Acid is 0-6, 7 is neutral, and 8-14 is alkaline. For you science nerds, soil pH is the negative logarithm of the hydrogen ion concentration. As hydrogen increases, soil pH becomes more acidic.
Finding Your Soil’s pH
The best way to find your soil’s pH is to do a soil test. You take a sample of soil and send it to the soil lab in your state or area. In Texas, that is Texas A&M University soil lab. Your Extension agent can tell you where to send your soil test. There are also soil tests and soil pH tests sold online or at the nursery, but they are not as accurate.
You will receive your soil test results with how much nitrogen, phosphorus, and potassium is in your soil. Pay a little more and you will find out how much of the other nutrients are in your soil. The soil test results will also recommend the amount of fertilizer you need to add before you plant if you indicate what you plan to plant. The soil pH is also indicated, along with recommendations to adjust it if necessary for the plants you want to grow.
The best time to take a soil sample is in the fall so you get the results in time to adjust the pH. You will usually get the results in 7-10 days.
How Does Soil pH Affect Nutrient Uptake?
Soil pH affects nutrient uptake in two ways. First, nutrients must be dissolved in the soil before being available to plants. Water is necessary for dissolving these nutrients, which is why you are usually told to water after fertilizing. Synthetic fertilizers furnish nutrients in the form of ions that plants can absorb directly. Organic fertilizers must be eaten by soil microbes to change nutrients into ions the plants can absorb. Organic fertilizers take a little extra time to work because of this extra step.
Nutrients dissolve better in acidic conditions than in alkaline conditions. This is good and bad. Some nutrients are toxic when dissolved in the soil in high quantities, such as boron and phosphorus.
Soil pH also affects the amount of life in the soil. Soil microbes do better when soil is close to neutral. In acidic soil, the lack of microbes means organic matter isn’t decomposed to release their nutrients back into the soil. The soil becomes less fertile because of the scarcity of some nutrients. This sounds like it contradicts what I just said, but it doesn’t. There can be a shortage of some nutrients in acidic soil even as what is there is readily available.
If the pH is 7.5 or above, plants cannot absorb copper, zinc, iron, boron and manganese from the soil. You may have to apply these nutrients by spraying a foliar formation on the foliage. Pecan trees often require foliar applications of zinc.
If the soil is acidic, phosphorus absorption is a problem. Most of the nutrients that plants need can be absorbed by plants when planted in a soil with a pH of 6.5.
Why Soils Become Acidic
There are three ways soils become acidic. Rainwater may leach the nutrients that are considered base, or alkaline. These are calcium, magnesium, potassium and sodium.
Carbon dioxide is released into the soil when organic matter is decomposed and from the roots of the plant as it breathes. When the amount of carbon dioxide is high, it dissolves in soil water and forms a weak organic acid.
The third way soil becomes acidic is when nitric and sulfuric acid forms as organic matter decomposes and ammonium and sulfur fertilizer oxidize.
Changing Soil pH
Changing soil pH takes time. Traditionally, chemicals to increase acidity or alkalinity are added in the fall after the crops are harvested. They work over the winter so you can plant new things in the spring. The amount of these substances you need varies according to the current pH, soil texture, amount of organic matter, the plant you are growing, and your target pH. It may take years to make much of a difference in the soil pH, so it is better to pick plants that thrive in the pH you have.
Lime is typically used to make soil less acidic. Ground limestone is either calcic limestone or dolomitic limestone that is also high in magnesium. Wood ashes are sometimes used to make soil less acidic but using them is less precise than using ground limestone. Lime is generally safe to use but you should wear gloves and a dust mask, so it doesn’t get on your hands or lungs. Breathing lime can cause respitory problems.
Sulphur is used to increase the acidity of soil. It is also a secondary macro nutrient. Use a dust mask to spread it because sulphur in your respitory system is a bad thing. Sulphur takes longer to change the pH than lime does. Microorganisms in the soil eat the sulphur and change it into sulphuric acid, which is what changes the pH.
Acid Loving Plants
Some plants have evolved to grow well in acidic soils. Strawberries like slightly acidic soil. Dogwood trees like soil with a pH of less than 6.8. Blueberries grow best in soil with a pH of 5.5. Azaleas, rhododendrons, and conifers like pine trees also grow well in acidic soils. Blackberries, however, like neutral or slightly alkaline soils.
Many companies make fertilizer with acidifiers in it just for acid loving plants. Using ammonium sulfate as a fertilizer will also make the soil more acidic.
We Can Help
Tennessee Wholesale Nursery can help you find a plant that will grow in tough pH conditions. Give our sales staff a call at 931.692.7325 today to get started.
