What is soil pH
Soil pH is the measurement of soil’s acidity or alkalinity. It is based on a scale of 0 to 14 with zero being the most acidic a substance can be, and 14 the most alkaline. A pH rating of 7 is considered neutral. Soil with a pH above 7.0 is considered alkaline, while soil with a pH less than 7.0 is said to be acidic.
Several factors go into determining soil pH, including the time of year, amount of rainfall, soil type, organic matter, soil microorganisms, and chemical fertilizers.
Why pH is Important
Each plant has a preference when it comes to pH levels. If you are unsure about the preferred pH for the type of plants you are growing, I have provided a chart in my article, Soil pH and Why It’s Important that lists the ideal pH level of sixty different vegetables and herbs. If the pH level is too high or too low for a particular plant, the nutrients in the soil will be inaccessible. A lack of nutrients can result in a weakened plant that is more susceptible to disease and insects. What’s more, if it does not have access to nutrients it will eventually die. So what you may think is a nutrient deficiency in the soil may actually be a problem with the availability of those nutrients due to improper pH levels.
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Test Soil pH
Proper soil pH is important to the overall health of the soil and therefore the health of your plants. The only way to know definitively the pH of the soil is to test it periodically. It is also a good idea to test nitrogen (N), phosphorus (P), and potassium (K), especially considering that correcting pH may also alter nutrient levels. Thankfully, there are soil test kits that can test both the soil pH and the NPK levels. (You can learn more about NPK in this helpful article.) Alternatively, there are also soil meters that test only for soil pH. Both are quick, easy, and convenient to use, and the results are available in a matter of minutes.
Another option would be to have your local county extension office perform a soil test. Although you will need to send in a soil sample, and it could take up to several weeks to receive the test results, it will be a more comprehensive analysis. The Helpful Gardening Links section of my Resource page will provide you with a link to help you find the county extension office nearest you.
How to Lower Soil pH (Make it More Acidic)
If the soil test reveals that your soil is too acidic, you can learn how to remedy the problem in 4 Ways to Raise Soil pH (Make it More Alkaline). Or, if the soil test reveals that your soil is too alkaline for the type of plants you want to grow, there are several ways you can lower the pH to make it more acidic:
1. Sulfur or elemental sulfur is one of the most common and effective methods for lowering soil pH. This organic amendment is easy to use in a pelletized form. It should be worked into the soil to a depth of several inches. Keep in mind that it can take several months or up to a year for the naturally occurring bacteria in the soil to convert the sulfur to its usable form, sulfuric acid. The biological process takes place when the bacteria are active, which is in soil temperatures are 55o F and above. Be sure to follow package for directions and safety protocol. If you have heavy clay soil, sulfur may be the best option.
2. Compost is believed by many to be one of the best ways to lower soil pH over time. As you add mature compost to your garden it will naturally make the soil more acidic, and you will have the added benefit of improving the soil structure and adding in microorganisms. Consistent use of compost over time is also believed to help stabilize the soil, thus, eliminating the need to alter the pH each growing season. Compost tea is also an option.
3. Peat Moss is an organic material that gradually helps lower soil pH. Some recommend adding one to two inches of peat moss to the top of the soil and then working it into a depth of several inches.
4. Mulch not only helps soil retain moisture, but it can slowly add acid to the soil as it decomposes. While there is some discussion as to whether pine needles contribute more acid to the soil than other organic matter, the consensus is that the amount of acid is negligible. If the pine needles have been composted, the process is thought to have neutralized any acid.
5. Organic Coffee – While coffee grounds are good for adding a little nitrogen to the soil, contrary to popular myth, they are not a good method for lowering soil pH. The acids in the coffee are released into the water when brewed making the grounds almost pH neutral. Freshly brewed coffee, on the other hand, has an average pH of 4.5. Some suggest diluting the coffee with water (50-50) and once cooled, using it to water your plants that require more acidic soil.
6. Organic Vinegar is an inexpensive household item that can quickly lower the pH of your soil. But white vinegar, for example, is highly acidic with a pH of 2.4, therefore, caution should be exercised because it may overcorrect the problem. What’s more, if the soil is very alkaline it will neutralize the acidity of the vinegar rendering the treatment ineffective. Others caution using vinegar because it can change the pH too rapidly and kill off beneficial soil organisms. So while vinegar is a cheap and fast-acting way to potentially lower soil pH, it is perhaps not the best long-term solution.
7. Aluminum Sulfate or alum as it is also referred to, is a synthetic chemical fertilizer that is sometimes recommended as a means to lower soil pH because it works almost immediately. However, you must be very careful in handling it as it can be harmful to humans. You will also need to be very precise in its application as too much aluminum sulfate can cause toxicity in the soil. In my opinion, I would not use it as there are other options available that are safer and better for you and the environment.
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