The Complete Guide to Lowering Soil pH
Soil pH plays a vital role in plant health, influencing both nutrient availability and root development. When the pH is too high, the soil becomes overly alkaline, creating conditions that can stress or even kill plants that prefer neutral or acidic environments. If your soil is too alkaline, don’t worry—this article will show you how to lower soil pH effectively to create the ideal soil conditions for your plants.
Why Should We Reduce pH Level in Soil
The pH value measures how acidic or alkaline a substance is, on a scale from 0 to 14. A pH of 7 is considered neutral; values below 7 indicate acidity, while values above 7 indicate alkalinity. The pH scale is logarithmic, meaning each one-unit change represents a tenfold difference in acidity or alkalinity.
When soil pH is too high, typically above 7.5, it can reduce plant health and lower soil productivity. Alkaline soils make it harder for plants to absorb important nutrients like iron, phosphorus, manganese, and zinc, even when those nutrients are present in the soil. This often leads to nutrient deficiencies and poor growth.
In addition to high pH causing alkalinity problems, you may also need to lower your soil pH when growing plants that prefer acidic soil. While many vegetables, fruits, and ornamental plants grow well in neutral soils (pH 6.5 to 7.5), some plants—such as camellias, rhododendrons, and ferns, grow best in more acidic conditions. If you want to grow these types of plants in your garden or pots, it’s important to make sure the soil has the right pH level.
How to Test pH of Soil
The first step in lowering your soil pH is to know your current soil pH level. While there are several methods for measuring soil pH, we recommend using a soil pH meter if you want a relatively accurate and cost-effective option.
pH Meter
Start by collecting a soil sample from the area you want to test. Dig about 4 to 6 inches deep, as surface soil may differ from the root zone. Remove any debris, such as stones or organic matter, and mix the soil to ensure a uniform sample. Insert the pH meter’s probe into the soil and wait for the reading to stabilize, which usually takes about 30 to 60 seconds. Take multiple readings from different spots to ensure consistency.
Testing Kits
You can also get testing kits in local shops around you. To use them, mix a small amount of soil with distilled water as directed, then dip the test strip or add the reagent. Compare the resulting color to the provided chart to determine the pH. While not as precise as a digital meter, these kits are widely available in gardening stores and provide a good estimate for home use.
Kitchen Supplies
You can also use kitchen supplies to get a rough idea of your soil’s pH. Start by mixing 1 tablespoon of soil with 2 tablespoons of distilled water and stirring thoroughly. Let the mixture sit for a few minutes, then pour it through a coffee filter to separate the liquid. Divide the filtered liquid into two small containers. Add vinegar to one container—if it fizzes, your soil is alkaline. In the other container, add a pinch of baking soda mixed with water—if it fizzes, your soil is acidic.
Lab Tests
For the most accurate results, you can send your soil sample to a professional lab for testing. Many agricultural extension services and private labs offer soil testing for a fee. However, this method is more time-consuming and costly, so it's generally recommended only for gardeners with specific needs or those requiring precise results.
How to Lower pH in Soil With Amendments
Common soil amendments include sulfur, aluminum sulfate, iron sulfate, or organic matter. It's best to make these changes before planting, because once plants are in the ground, adding amendments risks damaging their roots. Soil pH changes slowly and might take weeks or even months to see the full effect. After the initial application, it’s a good idea to test the soil again. If the pH hasn’t reached the desired level, you may need to repeat the process with additional amendments.
Sulfur
Elemental sulfur is one of the most effective and widely used methods for lowering soil pH. It works by reacting with soil bacteria, which convert the sulfur into sulfuric acid. This chemical reaction gradually makes the soil more acidic. Because it relies on microbial activity, the process is faster in warm, moist soils and slower in cool or dry conditions.
The amount of sulfur needed depends on your soil type. Sandy soils usually require about 1 pound of sulfur per 100 square feet to lower the pH by one unit. Loamy soils may need 1.5 to 2 pounds, and clay soils can require up to 3 pounds. Spread the sulfur evenly over the area you’re treating and thoroughly mix it into the top 6 to 8 inches of soil using a shovel, garden fork, or tiller. After applying, water the area well to help activate the process. Since sulfur acts slowly, retest the pH after four to six months before deciding if additional applications are necessary.
Aluminum Sulfate
Aluminum sulfate is another option. Unlike elemental sulfur, it lowers pH immediately upon dissolving in water. This makes it ideal for situations where you want to see changes quickly. However, it should be used cautiously—especially in sandy soils—because excessive use can lead to aluminum buildup, which may harm plant roots over time.
A typical application rate is about 5 pounds per 100 square feet to lower the pH by one unit. Distribute the aluminum sulfate evenly and mix it into the top 6 to 8 inches of soil. Water the soil thoroughly to help the material dissolve and take effect. Because of its rapid action, it’s important to test the soil again after a few weeks to make sure you haven’t over-acidified the soil.
iron sulfate
Iron sulfate is another amendment commonly used to lower soil pH. It works in a similar way to elemental sulfur, producing sulfuric acid as it reacts with the soil. However, it tends to act faster because it doesn’t rely as much on microbial activity, making it a good choice when conditions are less favorable for soil bacteria, such as in cooler or drier climates.
The recommended amount of iron sulfate is typically around 4 to 5 pounds per 100 square feet to lower the pH by one unit, depending on your soil type. Spread the material evenly over the target area and mix it into the top 6 to 8 inches of soil. After application, water the soil thoroughly to help the material react. Be sure to test the soil again after several weeks to assess whether additional adjustments are needed.
Organic Matter
Organic matter such as peat moss, composted oak leaves, pine needles, and pine bark can also help to lower soil pH, though more gradually. This method is ideal for gardeners who prefer a natural and sustainable approach.
To apply, spread a 2 to 3-inch layer of organic material over the soil and work it into the top 6 to 8 inches. Peat moss is especially effective and can make a significant difference when used in generous amounts. While results won’t be immediate, organic matter offers additional benefits. It improves soil structure, boosts microbial activity, and increases moisture retention.
To Round Up
Lowering soil pH is a gradual process, but with the proper amendments and consistent care, you can create the ideal environment for your plants. Whether you choose sulfur, aluminum sulfate, or organic matter, each method requires patience, as soil pH changes slowly. It’s essential to test your soil regularly to track progress and make necessary adjustments.
