What is Acidic Soil? 

soil ph tester placed in a soil

Acidic soil may seem like the be-all to end-all of plant growth, but it has unique characteristics that don’t necessarily mean a death sentence for your yard. Controlling pH levels is extremely important for healthy plant development. Soil tests, amendments, and care are vital to successful gardening.

Learn about what acidic soil is, what causes it, and ways to prevent a detrimental amount in your yard.

meant by acidic soil
Infographic by Juan Rodriguez

What is acidic soil?

Soil acidity is a type of degradation that leads to nutrient deficiencies and toxicity development, all of which prevent healthy plant growth. The acidity of any substance is measured in pH units on a scale of 1 to 14. On this scale, pH 7.0 is the neutral point, with everything ranking below that considered acidic and everything above that as alkaline or basic.

Acidic soils sit at around 5.0 on the pH scale, way below the 6.0 to 7.5 level most garden plants need to thrive. When a plant has the ideal pH, phosphorus, one of the key macronutrients essential for plant development and growth, becomes soluble and easily absorbed. Acidic soils prevent this process, making it harder for plants to access needed nutrients.

For an in-depth look at the various soil acidity levels, take a look at our table below.

pH levelAcidity levelDescription
4.0Extremely acidicSoil structural breakdown is inevitable. The soil loses its fertility and ability to support plant or grass growth.
4.5Strongly acidicBacterial activity is almost non-existent. Aluminum and manganese become toxic, especially if the right temperature and moisture conditions are met. Plants can’t absorb nutrients, preventing or limiting growth.
5.0Moderately acidicReduced phosphorus availability for plant intake, resulting in dull leaves and stunted plant growth.
5.5Slightly acidicA good balance of trace elements and nutrients for plant development.
6.0Close to neutralOptimal pH level for acid-vulnerable plants.

Causes of acidic soil

Soil acidity can be influenced by the climate and the material from which the soil was formed. It also can result from improper agricultural practices, which are more common than expected. 

Let’s look at the five leading causes of soil acidity.

Excess irrigation or rainfall

When soil is exposed to large amounts of water in a short time, acidity can form. Whether due to rainfall or excessive irrigation, too much water will wash key nutrients out of the topsoil, including alkaline ones like magnesium, potassium, sodium, and calcium. With these elements missing, pH levels drop, and the soil becomes acidic.

Organic matter buildup

As organic matter decomposes, it releases carbon dioxide, which creates carbonic acid when it comes into contact with water. As acids increase in the soil, so does the level of hydrogen. The higher the hydrogen content in relation to basic agents (calcium, magnesium, and potassium), the more acidic the soil.

Too much high-nitrogen fertilizer

Nitrogen is an essential macronutrient used for soil and plant health, but as with anything, too much of a good thing is a bad thing. Nitrogen fertilizers contain ammonia, a compound that is transformed into nitrates in the soil. Nitrates release hydrogen, which in turn increases soil acidity. To prevent this process and many headaches down the road, avoid feeding your soil more high-nitrogen fertilizer than it needs.

Acidic parent materials

Soil pH is inherently affected by soil-forming elements such as the parent material. The minerals in the parent material contribute to the condition of the soil – the higher the acid content of the parent material, the more acidic the newly-formed soil.

Crop removal

Crops balance acid (anion) elements and base (cation) elements in the soil. Anion elements include nitrate, sulfate, and phosphate, while cation elements are generally potassium, magnesium, and calcium. 

By nature, plants absorb more cations, which means the material is predominantly alkaline or basic. The excess removal of crops, and failure to return them to the soil when they die, causes an electrical imbalance, as the alkaline presence of plants can no longer cancel out the anions produced by other processes.

Pros and cons of acidic soil

acidity affect plant growth
Alandmanson | Wikimedia Commons | CC-BY-4.0

Though acidic soil isn’t generally helpful for healthy plant and grass growth, it’s not all bad. Here’s why acidic soil may be beneficial or detrimental, according to case:

Pros of acidic soil

  • When your soil has a pH level of about 5.5, it has a good balance of the major nutrients and trace elements plants need to thrive. 
  • Earthworms and many other soil-dwelling organisms and microorganisms love acidic conditions. They convert nitrogen into a usable form to aid healthy plant growth.
  • Many acid-loving plants, flowers, and vegetables thrive in acidic soils. These include:
    • Mountain laurels (Kalmia latifolia)
    • Azaleas (Rhododendron spp.)
    • Rhododendrons (Rhododendron spp.)
    • Hydrangeas (Hydrangea spp.)
    • Daffodils (Narcissus)
    • Tomatoes (Solanum lycopersicum)
    • Blueberries (Vaccinium sect. Cyanococcus)

Cons of acidic soil

  • Acidity levels below 5.5 limit the ability of plants to take up iron, phosphorus, and other important nutrients, preventing proper plant development.
  • When soils are overly acidic, plants can’t absorb water to the best of their abilities. Without water, plants can’t grow, photosynthesize, cool down, or absorb nutrients and minerals.
  • In the presence of extreme acidity, soils become less fertile, lose their ability to sustain plant growth, and break down structurally. This leads to erosion and general deterioration.
  • Acidic soil plays a role in reduced microbial activity. Microorganisms are responsible for breaking down organic matter and making nutrients more available for intake. Typically, the ideal environment for microorganisms is a pH level between 6.0 and 7.0.

How to determine if your soil is acidic

gardener measuring soil ph using a monitor
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A soil test can let you know what your soil’s pH levels are. Go around your lawn and gather samples from several locations. Try various depths for optimal results (up to 12 inches). Send the samples to your local Cooperative Extension Office to establish your soil’s pH, nutrient levels, and deficiencies. For help with the results, refer to our guide on “How to Read a Soil Test Report.”

If you’re a do-it-yourselfer, an at-home soil test is another way to determine if your soil is acidic. Garden centers and nurseries sell a variety of easy-to-use and budget-friendly soil pH testing kits.

Here’s how to perform a soil test at home:

  • Scrape away any litter, leaves, or plant residue from the surface of the soil. Avoid spots where you dumped manure or ashes, sorted compost, or burned something, as this could alter the results.
  • With a trowel or shovel, dig a 6- to 8-inch-deep hole in the soil. Collect your sample and repeat the process in several other locations in the yard.
  • Mix the various samples in a clean bucket or jar and add enough water to reach the soil level. Stir the mixture vigorously, then let it rest for 30 minutes.
  • Use a coffee filter to drain the soil solution into another clean container, making sure no solids pass through.
  • Dip the pH test strip into the resulting liquid, following the instructions on the package. Don’t leave the strip in the liquid longer than advised.
  • Compare the color with the chart given on the packaging to determine the pH. 
  • Repeat the entire process several times to get an average pH reading.

Ways to fix soil acidity

While fixing soil acidity is certainly possible, it’s a process that takes time and won’t be achieved in one go. Maintaining your desired pH level also may require regular effort on your part.

Before making any soil amendments, perform the above-mentioned soil test to know what pH levels you’re working with. Then, add one or a combination of the following elements to your soil:

1. Limestone

Adding lime to your soil (or liming your soil) is the easiest and most cost-effective way to adjust acidic pH levels. This replaces hydrogen ions in the soil and eliminates major issues associated with a low pH (or acidity). It also hastens the decomposition of organic matter and makes macronutrients more readily available for plant intake.

Limestone can be pure calcium carbonate or a combination of magnesium and calcium carbonate (also known as dolomite). In addition to being easy to handle, limestone won’t leave harmful residues in your soil.

The appropriate quantity of lime needed to correct soil acidity is determined by the soil texture (sand, clay, and silt), soil pH, nutrient status, the amount of organic matter in the soil, and the type of plants you want to grow. Get to know your soil and do your research before getting started. After one application, retest your soil to see if the lime has had an effect.

2. Wood ashes

If you’d rather go another route, consider using wood ashes to reduce your soil’s acidity. To avoid the risk of harming existing plants, make sure the ash doesn’t come from wood that’s been treated. Choose a non-windy fall day to apply around 5 to 10 pounds of wood ash per 100 square feet of yard space. Push the ashes firmly into the ground. Perform a soil test every once in a while to determine the ashes’ effectiveness.

3. Compost

Due to its alkaline nature, compost can increase the base ions present in soil, successfully alleviating soil acidity. This method takes time, so continue adding compost to your yard yearly to provide your plants with essential nutrients. 

FAQ about acidic soil

How long will it take to decrease my soil’s acidity level?

After applying limestone or another neutralizing agent to your soil, it can take three to six months for pH levels to show significant change. The timeframe can vary, depending on the frequency of the applications and other factors that affect soil acidity.

How can I maintain healthy soil?

Healthy plant-, fruit-, and vegetable-generating soil requires airflow, water, nutrients, and care. As long as you maintain a robust soil ecosystem, your garden will explode with goodies. 

What if my acidic soil becomes too alkaline?

If your soil has gone too far in the opposite direction of the pH scale, add aluminum sulfate, elemental sulfur, or sulfuric acid to it. Keep in mind that sulfuric acid, while a quick fix, is hazardous to plants. Instead, opt for one of the other two options available to homeowners. Aluminum sulfate reduces pH levels faster since it’s soluble, but elemental sulfur is more budget-friendly, something to keep in mind if you need to cover a larger area.

Get expert lawn care help

Fixing acidic soil can be a headache if you don’t know much about it. Even after proper documentation, you may realize it’s not something you want to take up.

To bypass the confusion and physical labor associated with acidic soil amendments, why not reach out to a local lawn care pro instead? They’ll help you achieve healthy soil, grow striking plants, and enjoy plenty of delicious vegetables.

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Andie Ioó

In my free time, I enjoy traveling with my husband, sports, trying out new recipes, reading, and watching reruns of '90s TV shows. As a way to relax and decompress, I enjoy landscaping around my little yard and DIY home projects.