How to Increase, Decrease, & Measure Soil pH Levels

A soil’s pH determines which nutrients and chemicals are able to survive, so maintaining a stable pH is essential if you’re trying to grow healthy crops or plants. Luckily, there are a number of common materials you can add to soil to adjust its pH level. In this article, we’ll show you how to raise and lower soil pH levels, as well as how to evaluate your soil to determine the changes you need to make. Plus, find out what pH is, why it’s important, what factors influence it and answers to other common questions about adjusting soil pH.

How to Adjust pH in Soil

Test your soil’s pH level to see if it needs to be increased or decreased.
Raise soil pH by tilling in a lime-based material, wood ash, or baking soda.
Lower pH by adding sulfur, organic material, or an ammonium-containing fertilizer.

Section 1 of 7:

How to Raise Soil pH

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1
Apply lime to effectively raise the soil’s pH. To raise the pH of soil and make it more alkaline, you need to introduce a base (an alkaline material), like a liming material. There are numerous lime-based materials to add to soil, including hydrated lime, fluid lime, burned lime, calcitic lime, and dolomitic lime. In general, it’s best to use as finely ground lime as possible, as this increases the surface area in which the soil can react to it. The amount of lime needed depends on a variety of environmental factors, like the type of soil and its existing pH level.^{[1]
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- Expect to see results from lime within a few months to a year.^{[2]
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  Research source} It isn’t the quickest method to raise soil pH, but it is often considered the most effective and is popular among gardeners.
- To know how much lime to add, consult an extension or government website in your region. These typically have charts that explain how much to add depending on the type of soil you have, its original pH level, and your desired pH level.
- Pulverized lime is finely ground and more easily absorbed by the soil. However, it is more difficult to spread because it can clog the applicator.
- Granular and pelletized lime are easier to spread. However, they’re not as effective at altering the soil pH.
- Hydrated lime should only be used with extremely acidic soils since it is more water-soluble and can quickly increase a soil’s pH.
- Some lime products contain additional micronutrients like dolomite, which is a mixture of calcium and magnesium carbonates. These are a great option if your soil is also missing some key nutrients!
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Mix wood ash into the soil to also remove impurities. The ash of burned trees is quite alkaline (basic) and contains micronutrients like calcium, potassium, phosphate, and boron. It also absorbs waste in your soil, which is great if your soil has been neglected. Wood ash is more soluble and reactive than limestone, so it may raise the pH more quickly, but more wood ash is needed than lime to make the same impact on the soil.^{[3]
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- Wood ash works well in sandy soil because it breaks down and mixes with the sand particles over time.
- You can burn wood yourself and collect the ash, or purchase a wood ash fertilizer.
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Choose baking soda if you’re worried about harming plants. Some plants can be a little sensitive to wood ash and lime, so just use baking soda if you don’t want to irritate anything you’ve already got growing in your garden or yard.^{[4]
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Research source} Baking soda can produce results within a few days and is cost-effective, but it doesn’t last very long as it isn’t formulated for agricultural use.
- Add pulverized eggshells to the baking soda if you’d also like to increase the calcium levels.
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Mix the liming source in the soil 2-3 months before planting. In order to get the best results, till the liming material into the soil about 2-3 months before planting in the fall or winter. This will give the soil’s pH time to change and allow you to remeasure it. Till the lime, ash, or baking soda into the soil’s root zone, which is 7–8 inches (18–20 cm) below the surface of the topsoil.^{[5]
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- You can spread the lime by hand if you have a small enough piece of land. Or, use a spreader to apply liming material to a yard.
- Use a rake or a rototiller to work the liming material into the soil.
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Water the soil regularly after increasing the pH. Lime will have little effect on dried out soil, so apply water regularly. Water activates the lime and helps it seep into the soil. Use a garden hose or sprinkler to apply water every other day or so until your soil pH reaches your preferred level.^{[6]
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- Don’t water if you’ve already got moist soil. Overwatering can leech other minerals out of the soil.

Section 2 of 7:

How to Lower Soil pH

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Add sulfur to the soil to efficiently lower pH. Compounds containing sulfur are often used to intentionally make soil more acidic—elemental sulfur, iron sulfate, and aluminum sulfate are all good options. The sulfur reacts with bacteria in the soil to lower the pH, so it’s often more challenging than raising soil’s pH. The amount of sulfur you need depends on the type of soil you have and its original pH level.^{[7]
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- It typically takes a few months to a year for sulfur to lower pH.
- In cooler climates, soil temperature affects biological activity. Soils need to be in the right conditions for bacteria to be active in order for the sulfur to work.
- Whether you use sulfur or another amendment, the amount you need will depend on a number of environmental factors. For the best results, check extension or government websites for your region to determine how much you’ll need.
- For example, this chart explains the application rate of sulfur based on the soil’s texture and desired pH change.
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Try an ammonium-containing fertilizer. Ammonium-containing fertilizers like ammonium sulfate, urea, and ammonium nitrate also help lower the pH of soil. When these fertilizers are added to your soil, they create sulfuric acid, which assists in decreasing the pH.^{[8]
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- These fertilizers may work a bit more quickly than sulfur, as the pH often decreases within 3-6 months after application.^{[9]
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Use organic matter to reduce pH by a small amount. Organic materials like pine needles, compost, and manure can slowly lower your soil’s pH. As the matter begins to break down, organic acids are sent directly to the soil. The amount of acids is considerably smaller than other pH lowering methods, though, so this option is best if you only need to lower the pH slightly.^{[10]
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- Using organic matter is a slow process, so it can take years to completely repair the soil. While it’s possible you may see some results a bit earlier, choose this method if you’re okay with a gradual process.
- Organic matter is also useful for improving a soil’s drainage and aeration.
Lowering soil pH is a slow, gradual process that won’t happen overnight. By applying sulfur, fertilizer, or organic material at least a year before planting, it will have more time to react with the soil and start changing the pH. The larger the change needed, the more time it will take, so plan accordingly based on your starting pH level and your desired level.^{[11]
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Mix the organic compounds, sulfur, or ammonium-containing fertilizer into the soil so that it can begin reacting. Organic compounds may require multiple applications depending on how high the pH is. Test the soil before reapplying.^{[12]
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If the sulfur or aluminum sulfate gets on the leaves of your plants, rinse it off with a hose. Otherwise, simply water any existing plants to help flush any excess acid. Continue reapplying the material and testing your soil until you’ve got a reasonable soil pH.^{[13]
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Section 3 of 7:

Evaluating Your Soil’s pH

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Identify the type and texture of your soil. Before you test your soil or add anything to it, determine what type of soil you have. Examine your soil to see if it’s clumpy, dry, loose or wet. Then, assess what kind of material is in your soil, such as sand, loam, clay, or muck. This will give you some clues about what altering the soil may entail.^{[14]
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- Well-drained and loose soil will be easier to adjust. On the other hand, compacted soil that has a lot of clay in it will be more difficult to change.
- Determining your soil type will help you figure out the best method for applying any materials to it.
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Test the soil’s pH with a digital probe or test strips. Once you have an understanding of soil pH and the type of soil you are dealing with, test it to determine its pH level.^{[15]
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Research source} Either buy a commercial test and send it into a lab, or just test the soil yourself with a digital probe or test strips. The easiest way to test your soil is to dig a hole, fill it with water, and then insert a test probe into muddy water.
- There are also some DIY methods that involve making your own pH test strips, although you’ll get much more accurate readings if you use a product designed for this.
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Research the soil pH preferences of the plants you’re growing. The type of plants you intend to grow will determine what soil pH level you need. Many plants prefer a more acidic soil, particularly flowers and some fruit plants like blueberries.^{[16]
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Research source} Research what the recommended pH levels are for the plants you want to grow.
- Most plants grow best with a soil pH between 6 and 7.5, though 6-8 is acceptable. Some prefer more acidic soils, however, like azaleas, rhododendrons, and blueberries (pH 4.5-5.5), and some vegetables, grasses, and ornamentals prefer slightly acidic soils (pH 5.8-6.5).
- On the other hand, plants like hydrangeas, lilac, and lavender can grow in more alkaline soils.
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Leave your soil alone if the pH is around 7. Most plants prefer a pH between 6 and 7.5. A 7.0 on the pH scale is neutral, meaning most of the required nutrients (and helpful earthworms and microorganisms) will be available in the soil. A range of 6-8 is considered acceptable for most plants, although certain specialized plants require higher or lower pH levels.^{[17]
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- If your soil is way too acidic, plants will die as the roots get fried in the toxic soil. If the soil is too alkaline, they may not get the nutrients and minerals they need to thrive.
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Test your water’s pH to see if that’s the core issue. If your soil appears to be healthy but you’re still having problems keeping plants healthy, it could be the pH of your water. Groundwater, the water used in most homes and gardens, tends to be more alkaline. However, rainwater tends to be more acidic. Use water testing strips to assess the pH of your water.^{[18]
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- If your water is the problem, either start buying pH-balanced water for your plants, or adjust the soil to compensate for the especially high or low pH of the water.

Section 4 of 7:

What is soil pH?

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Soil’s pH describes its acidity or alkalinity. The pH scale ranges from 0 to 14, with 7 being neutral. Soil with a pH above 7 is alkaline, or sweet, while soil with a pH below 7 is acidic, or sour. Different plants prefer different pH levels, though in general, neutral soil provides most of the nutrients plants need.^{[19]
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- For example, blueberries and azaleas prefer acidic soil at a pH of 4.5-5.5.

Section 5 of 7:

Why Soil pH is Important

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Soil pH determines nutrient availability for plants. Each nutrient in soil has an optimal pH level at which it will thrive. Certain nutrients are more available in slightly basic or acidic soils, though most are not available at either extreme end of the scale. In general, nutrients are best available at a fairly neutral pH level of 6.5-7.0.^{[20]
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- For example, if a soil has a pH of 5.5 or below, nutrients like phosphorus, potassium, and others become more tightly bound to the soil, making it difficult for plants’ roots to absorb them.
Monitoring your soil’s pH is also important because it can develop aluminum toxicity if it drops to 4.5 or below; this means a higher amount of metals are entering your soil, which could damage crops. Only acid-loving plants like blueberries and azaleas can thrive in this soil, so if you want to grow anything else, it’s best to add lime to raise the pH.^{[21]
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Section 6 of 7:

Natural Factors that Impact Soil pH

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Rain is one of the most important factors regarding soil pH, as rainfall can wash away basic substances like magnesium, potassium, and calcium. In turn, this allows acidic substances like hydrogen and aluminum to have higher concentrations, making the soil more acidic. In areas without a lot of rainfall, soils tend to be more alkaline.^{[22]
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Soil texture A soil’s texture often determines its chemical properties, and pH levels differ considerably among clay, sand, and silt soils. It’s usually more difficult to lower the pH of clay soils than sandy soils, for example, while sandy soils may easily become too acidic.^{[23]
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- A soil’s ability to resist a change in pH is called its buffering capacity. This is especially important when attempting to lower pH. Clay content and organic matter play a large role in a soil’s buffering capacity.

Section 7 of 7:

Adjusting Soil pH FAQs

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Sulfur and ammonium fertilizers will help lower soil’s pH. Some examples of these fertilizers include ammonium sulfate, ammonium nitrate, and urea. On the other hand, nitrate fertilizers will raise the soil pH.^{[24]
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Fully adjusting soil pH is a slow process that often takes years. There are a few hacks (like using baking soda) to raise the pH quickly, but these methods don’t often have long-lasting effects. If you’re using limestone to raise your pH, you may see some results within a few months, but it may take a year or two to fully saturate the soil. Lowering pH also typically takes 1-2 years to see a complete reaction, though you may start seeing results within about 6 months.^{[25]
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While vinegar is acidic, it’s not effective at adjusting the pH of soil. It works better for changing the pH of liquids, as the soil’s pH will return to its original level when it rains and washes the vinegar away.^{[26]
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Soil pH depends on several environmental factors. For example, soils that receive less water and have a higher sand content typically have a higher pH. The continuous application of wood ash and alkaline amendments also play a role in a soil’s high pH level.^{[27]
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Is it better to plant in raised beds, or on the ground?

Steve Masley
Home & Garden Specialist
Steve Masley has been designing and maintaining organic vegetable gardens in the San Francisco Bay Area for over 30 years. He is an Organic Gardening Consultant and Founder of Grow-It-Organically, a website that teaches clients and students the ins and outs of organic vegetable gardening. In 2007 and 2008, Steve taught the Local Sustainable Agriculture Field Practicum at Stanford University.

Steve Masley

Home & Garden Specialist

Expert Answer

It depends on your budget and how much effort you want to put in. It's a lot harder to plant in-ground, but raised beds require a budget to buy the materials and construct the beds.

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Once the pH is within the acceptable range, how long will it stay that way? Is retesting the soil necessary? If yes, how often should I do it?

Katie Gohmann
Professional Gardener
Katherine Gohmann is a Professional Gardener in Texas. She has been a home gardener and professional gardener since 2008.

Katie Gohmann

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The soil will not stay that way forever. You'll want to retest your soil once a month until you discover a pattern. Soils will keep shifting pH according to what's happening beneath them, and you will need to continue to add soil amendments for whichever plants need them.

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What is the best way to decrease soil pH organically?

Katie Gohmann
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Katherine Gohmann is a Professional Gardener in Texas. She has been a home gardener and professional gardener since 2008.

Katie Gohmann

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Expert Answer

Lowering pH is hard because the limestone in the soil continually dissolves. If you don't want to use sulfur, try compost or composted manure with an acidic mulch, such as pine needles.

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Some claim that gypsum can help raise pH, but more authoritative sources say that this will not work, as gypsum is not a liming product.^{[28]
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Sometimes, nutrient deficiency in plants can be due to the availability of nutrients rather than a lack of them. This is why it’s important to know the best soil pH for the plants you’re growing.

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