How to Change Your Soil pH

Keeping your soil within a recommended pH range is essential for growing healthy grass and plants, as the soil pH influences nutrient availability and soil health.

When your soil is too acidic or alkaline, you can modify the soil pH to bring it back into the recommended range to prevent nutrient deficiencies or toxicities. Adding lime, wood ash, or oyster shell meal raises the soil’s pH, making it less acidic. Standard methods for lowering soil pH include adding elemental sulfur, aluminum sulfate, and iron sulfate.

Soil pH is something I’m very familiar with. As a graduate student, I tested hundreds, if not thousands, of soil samples to check their pH values and taught undergraduate students about soil pH in a soil fertility lab. Living in an arid Western climate, my soil has a higher pH level (~8.2 to 8.4), so I must amend it for a productive garden.  

What is soil pH?

Soil pH is the measurement of how acidic or alkaline the soil is. Chemically speaking, it tells you how many hydrogen ions (H⁺) are present. 

Soil pH is measured on a scale of 0 to 14, with 7.0 as the midpoint (neutral). More H⁺ ions result in pH values below 7.0 and acidic conditions; fewer H⁺ ions — or more hydroxyl ions (OH^–) — result in pH values above 7.0 and alkaline conditions.

Pro Tip: The pH scale is logarithmic. A change in one unit — from 5.0 to 6.0 — represents a ten-fold change in hydrogen ion concentration. A pH of 5 is 10 times more acidic than a soil pH of 6 and 100 times more acidic than a soil pH of 7.

What is the ideal soil pH?

If you quickly search online for the ideal soil pH, you’ll get a range of answers from different sources. The Natural Resources Conservation Service says 6 to 7.5 is optimal for crop growth; Penn State Extension recommends 6.2 to 6.8 for most plants; and Oregon State University says 5.5 to 6.0 for lawns. 

Generally, you want your soil to be slightly acidic to neutral — between 6.0 and 7.0 — for lawns, gardens, and most ornamental plants. 

It’s important to mention that some acid-loving plants like azaleas, blueberries, and rhododendrons need a soil pH lower than the recommended range. They like 4.5 to 5.5, so you might need to acidify your soil to accommodate them. 

Some plants can also tolerate acidic conditions outside the ideal range. Bahiagrass, centipedegrass, perennial ryegrass, tall fescue, and bentgrasses can tolerate acidic soil. Lilacs and lavender will tolerate slightly to moderately alkaline soils.

Pro Tip: Hire a lawn fertilization service or gardening service near you to balance your soil’s pH for a luscious, vibrant landscape.

Why is soil pH important?

The pH level is crucial to healthy plant growth because it affects many things, one of the most critical being nutrient availability.

Soil pH and nutrient availability

When soil pH strays too far from neutral in either direction, some nutrients in the root zone can become unavailable for plant uptake. When nutrients become unavailable, this leads to nutrient deficiencies, resulting in symptoms like stunted growth and yellowing of plant tissues. 

Others become highly available, depending on the specific nutrient and the pH conditions. When nutrients become highly available, this can cause toxicities, which may damage or kill your plants.

Unfortunately, the tricky part is nutrient availability doesn’t follow the same pattern across the different nutrients plants need for growth.

• As pH values decrease and conditions become more acidic, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium become less available for plant uptake. Iron, manganese, copper, boron, and zinc become more available and may cause toxicity symptoms.
• As pH values increase and conditions become more alkaline, phosphorus, potassium, sulfur, boron, and molybdenum become highly available and may cause toxicity problems. Nitrogen, calcium, magnesium, iron, copper, zinc, and manganese become less available.

Soil pH and disease problems

Lawn diseases are also impacted by soil pH. 

• Acidic soils have increased problems with Fusarium patch, take-all patch, and red thread.
• Alkaline soils see increased occurrence and more severe issues with lawn diseases like summer patch, Pythium blight, necrotic ring spot, fairy ring, and powdery mildew. 

Factors affecting soil pH

Soil pH is affected by many factors. Parent material and the resulting soil type give your soil its inherent pH, but other factors can change it over time, even if you’ve worked hard to get the pH within the recommended range.

Parent materials are a significant contributor to soil pH

Parent materials are the big rocks found deep in the ground that break down to make different soils. Their mineral content determines a soil’s initial pH. 

• Soils formed from limestone tend to be alkaline because of the calcium carbonate in the parent material. As calcium carbonate breaks down, it neutralizes acidity by pulling H⁺ from the soil.
• Soils formed from granite or shale are usually acidic. These parent materials contain minerals that release H⁺ as they weather. 

Soil type impacts pH

Soil type affects soil pH because of texture (the size of the soil particles), which influences how the soil particles attract and hold onto positively charged molecules. 

Clay soils are usually more alkaline. Their small soil particles have an incredible amount of surface area, which gives them the ability to hold onto cations very tightly. They have an affinity for calcium (Ca²⁺) and magnesium (Mg²⁺), which are larger and have a stronger positive charge, instead of hydrogen (H⁺) ions, which are smaller and weaker. The high concentration of Ca²⁺ and Mg²⁺ over H⁺ contributes to the higher pH. 

Changing clay soil’s pH level is harder than sandy soil. Calcium and magnesium are held so tightly to the clay particles that they are hard to “knock off” and replace with H⁺ to lower the pH.

Meanwhile, sandy soils are more likely to be acidic. Rain and irrigation water washes away larger cations like calcium, potassium, and magnesium, leaving the smaller hydrogen behind. Sand also holds onto cations less tightly than clay, so replacing the base cations with hydrogen and acidifying the soil is easier.

See Related:

• “Complete Guide to Different Soil Types”
• “16 Plants That Grow in Clay Soil”
• “Best Grass for Sandy Soil”
• “15 Plants that Do Well in Sandy Soil”

Rainfall makes soils more acidic

Precipitation also plays an integral part in soil pH. Generally, areas with heavier rainfall have lower soil pH. As mentioned above, rainfall leaches calcium, magnesium, and potassium cations out of the soil, leaving hydrogen ions behind and lowering the pH.   

Because of wetter climates, soils in the eastern half of the U.S. tend to be more acidic. Desert areas like Arizona and Idaho typically have higher soil pH, as leaching is less of an issue.

You also tend to see lower soil pH values in urban areas or areas of heavy manufacturing due to acid rain that acts as a natural acidifier. 

Note: Overwatering has the same effect as heavy rainfall, so water your lawn and garden appropriately. You can read more about proper watering in these articles:

• “How Often Should I Water My Lawn with a Sprinkler System”
• “How Often to Water Your Vegetable Garden (And More Watering Tips)”

Fertilizer and organic material break down into acid or alkaline materials

Soil amendments can also impact soil pH, depending on their components. According to the University of California Division of Agriculture and Natural Resources:

• Ammonium-based fertilizers acidify soil. As bacteria break down ammonium into nitrate, hydrogen ions are released, lowering pH. 
• Nitrate-based fertilizers don’t acidify the soil. Scientifically speaking, they may increase soil pH, making it more alkaline. As plants take in nitrate, they also pull in a hydrogen ion, reducing the concentration in the soil.
• Animal manure can make your soil more alkaline because it contains calcium and magnesium.
• Compost and potassium fertilizers don’t typically change soil pH.  

Note: While compost doesn’t necessarily change soil pH, adding compost to soils can help buffer future pH changes.

How to test soil pH

There are three options to check your soil’s pH level. Each has its pros and cons.

• Use an at-home soil pH test kit from a garden center or home improvement store. These test kits are cheap, convenient, and fast; however, the test strips only give an approximate value instead of a precise result. Test kits typically cost less than $10.
• Use a digital soil pH meter or tester from garden centers or online retailers. They provide a more accurate result than the test strips, but their accuracy depends on the type of tester you buy and how well it’s calibrated. In terms of price, they’re middle-of-the-road, costing from $10 to over $200. 
• Take a soil sample and send it to a soil lab for analysis. This method takes longer but reports an exact soil pH. A basic professional soil pH analysis costs $10-20. One benefit is you can add a nutrient analysis for $50 to $100, depending on the lab and the tests performed, and get detailed fertilizer recommendations.

Note: Using your local Cooperative Extension office for soil testing means you’ll pay only a small fee. Some states even offer soil testing for free during slow times of the year.

My Tip: In my opinion, don’t waste your money on cheap testers. Unless you spend $50 or more on a decent meter and purchase the calibration buffers, you’re better off buying a test strip kit for $10.

See Related:

• “How to Soil Test Your Lawn”
• “How to Read a Soil Test Report”

How to raise pH in soil 

If your soil is too acidic, it has too many H⁺ ions. To raise the pH, you will need to add soil amendments that replace the hydrogen with cations like calcium or magnesium.

Lime

Adding lime (calcium-based compounds) is the most common method to raise a soil’s pH level. Lime chemically reacts with hydrogen ions in the soil, neutralizing soil acidity. 

What type of lime should you use?

Calcitic and dolomitic limes are the most common liming materials, both made from finely ground limestone. 

• Calcitic limes (sometimes called agricultural lime) contain only calcium compounds: calcium carbonate, calcium hydroxide, and calcium oxide. 
• Dolomitic limes also contain significant amounts of magnesium carbonate. They work well in soils with magnesium deficiencies.

When choosing a liming material, you want to look at two characteristics — calcium carbonate equivalent (CCE) and fineness. 

• CCE compares the neutralizing ability of a material to pure calcium carbonate. The higher the CCE, the more effective the product, and the less you need to use. 
• The finer ground the material, the quicker it will work, as limestone is naturally insoluble in water. Mixing smaller and larger lime particles is good to see a long-term effect on soil acidity.

Note: Avoid using hydrated limestone. It acts fast but is caustic, making it very dangerous.

How long does lime take to work?

No matter the product you use, it takes time for the chemical reactions to occur. It can take up to six months before you see a significant change in the pH and two to three years to see the full effect of an application. Smaller particle sizes and mixing the lime into the soil well will help it work quicker.

How much lime to apply?

Okay, this is where it gets tricky. Recommended liming amounts vary widely depending on soil pH, texture, and buffering capacity. Slightly acidic soil can take between 20 and 50 pounds of calcium carbonate per 1,000 square feet to raise the pH. Heavy clays that resist pH changes may need upwards of 100 pounds. 

My Tip: If you know your soil is too acidic, the best thing to do is send a soil sample to a lab for analysis and get a liming recommendation. The results will tell you how much lime to apply per 1,000 square feet to get it to different pH values.

See Related:

• “Benefits of Lime for Your Lawn”
• “How to Tell Your Lawn Needs Lime”
• “How to Apply Lime to Your Lawn”

Wood ash

Wood ash is just what you think: the product left behind after burning wood. It is high in calcium and potassium and has been produced in the U.S. for its potash (for fertilizer) and alkali as far back as the 1700s. Like lime, the carbonates react with hydrogen in the soil to neutralize acidity and raise pH.

It takes much more wood ash to change your soil pH than lime, but it works quicker because it’s more water-soluble. Depending on the ash’s CCE, it may take two to four times as much lime.

Oyster shell meal

Primarily made of calcium carbonate, finely ground oyster shells are a natural alternative to traditional agricultural lime. It provides a slow-release source of calcium, so its benefits last several years. Oyster shell meal works a little slower than lime. You may see noticeable changes within a few weeks, but expect it to take months to see a significant increase.

How to lower pH in soil

Compared to making soil more alkaline, hydrogen ions are added to make your soil more acidic. Sulfur is the primary soil amendment used. However, it’s harder to make soil more acidic than to make it more alkaline, especially if you’re dealing with clay soil.

My Tip: You can use ammonium fertilizers or organic materials to lower soil pH, but you will need large amounts to make a difference. In my opinion, they are more suitable for helping to maintain a lower soil pH.

What kind of sulfur should you use? 

Elemental sulfur, aluminate sulfate, and iron sulfate are the top three amendments used by homeowners. 

• Elemental sulfur is the safest and least expensive option, but it works very slowly. It needs soil bacteria (and moisture) to break it down into sulfuric acid, and it may take three to six months to see a change. The smaller the particle size, the quicker it works.
• Aluminum sulfate works rapidly to change soil pH, reacting with water to form sulfuric acid. It is best suited for ornamental plants (like hydrangeas to turn them blue). Use caution in vegetable gardens and lawns because aluminum can be toxic at high levels.
• Iron sulfate works faster than elemental but slower than aluminum sulfate. It requires a larger quantity than elemental sulfur (about 8 times more) to see a significant pH reduction but also provides iron, which is beneficial for plants. 

Note: Avoid using straight sulfuric acid to lower your soil pH. It’s incredibly dangerous due to its caustic, corrosive nature.

Personal experience: I use a combination of elemental sulfur and iron sulfate to acidify my garden soil. I don’t typically try to adjust the soil pH for my lawn. So far, I haven’t seen major problems because of the higher pH (it typically runs 8.2 to 8.4 unamended). 

The elemental sulfur works well in areas where I till the soil in the spring — I can add the recommended amount and then work it in before planting. I use iron sulfate in my raspberry patch, where I don’t work the ground up. It gets watered in and starts working quickly, providing extra iron to my deficient soil.

How much sulfur to apply?

On average, to lower the pH by 0.5, you’ll want to apply 0.5 to 1.0 pounds of elemental sulfur per 1,000 square feet of soil. Sandy soils need less sulfur; clay soils need more.

Again, the best thing to do is to send a soil sample off for analysis so the lab can provide an exact recommendation.

Best practices for modifying soil pH

• Apply no more than 50 pounds of lime per 1,000 square feet of soil at any time.
• If possible, apply amendments when you don’t have plants growing. 
• Apply lime in the fall for maximum reaction time before spring planting.
• Apply sulfur products in the spring when the soil is warming up.
• Apply half of the product in one direction and the other half in a perpendicular direction.
• Work amendments into the soil if possible.
• Always water products into the soil well.
• Wash off sulfur that gets on your plants, or else it can burn the foliage.
• Check the soil pH every three months after amending to monitor changes.

FAQ about changing your soil pH

Let Lawn Starter Help With Your Soil

Changing your soil pH is just one step, albeit an important one, in having a beautiful lawn and garden. Once you reach an ideal pH, you still need to keep up with basic lawn care practices to maintain a lush, green landscape.

If you need help with mowing, fertilizing, aerating, gardening, or weed control, contact Lawn Love. We’ll put you in touch with a local professional who can take care of all your needs so you can enjoy a beautiful lawn and garden. 

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