If your soil pH is measuring either acidic or alkaline, there are ways to adjust it. The most common ways to change your soil pH are using lime to raise the soil pH and a sulfuric amendment to lower it. However, there are other soil amendments you can use, too.
What is soil pH?
Soil pH is the measurement of how acidic or basic the soil is. It is measured on a scale ranging from 0 to 14 with 7.0 as the midpoint (neutral); anything below 7 is acidic and anything above it is alkaline (basic).
The ideal soil pH for most plants is around 6.0 to 7.0, but there are some acid-loving plants like azaleas, blueberries, and magnolias. There are also some grasses that can tolerate acidic soil such as:
The pH level is quite important to healthy plant growth because it affects so many things:
- Soil nutrients are less available for plants to use in both acidic and basic soil. These include the three important macronutrients: nitrogen, phosphorus, and potassium.
- Some elements become toxic because they become more available in acidic soil. These elements include iron and aluminum.
- Diseases become more common in alkaline and acidic soils. Some of these lawn diseases are:
- Many yard weeds thrive in less balanced soil and can outcompete your already weakened plants. Some of these weeds include:
- Dandelions
- Clover
- Crabgrass
How to measure pH levels
There are two ways you can measure your soil’s pH levels:
- Using an at-home soil test bought at a garden center or home improvement store is convenient and fast. However, they’re not very detailed.
- Sending your soil to a soil lab takes longer but it is much more informative, telling you your exact soil pH as well as nutrient levels.
Read more:
What affects soil pH?
Soil pH is affected by many factors:
- Location
- Parent materials (rocks that make up the soil)
- Soil type
- Rainfall
- Fertilizer and organic material
- Soil amendments
Location influences other factors
Location plays a huge part when it comes to soil pH. Where you live influences soil type, parent materials, and climate. These three factors play a part in your soil’s pH level.
For example, the western half of the U.S. (minus the Pacific Northwest) tends to have alkaline soil.
Soil in the eastern half of the U.S. is more acidic. Areas that have more air pollution also tend to have more acidic soil due to acid rain. Usually, this means urban areas tend to have lower soil pH.
Parent materials are a big contributor to soil pH
Parent materials refer to the rocks that make up soil.
If your soil is made primarily of alkaline rocks, then your soil will have a higher pH. Your soil will have a lower pH instead if it’s made of acidic rocks.
Some soil types are more prone to acidity or alkalinity
Some soil types are more likely to be acidic or alkaline. Clay soils tend to be more alkaline as they hold more base (alkaline) cations. The Clemson University Cooperative Extension Service also notes that it’s harder to change the pH level of clay soil compared to sandy soil.
Meanwhile, sandy soils are more likely to be acidic as they hold onto less of these base cations. According to the Oklahoma State University Extension, sandy soils are also more prone to leaching, where water from rain and overirrigation washes away base cations like calcium, potassium, and magnesium in the soil.
Rainfall makes soil more acidic
We mentioned leaching above. Heavy rainfall means more leaching of alkaline materials, leading to acidic soil. Areas with heavier rainfall usually have lower soil pH. This acidifying effect is even worse in areas with acid rain.
That also means that areas with drier climates like Arizona have higher soil pH, as leaching is less of an issue.
Note: Overwatering has the same effect as heavy rainfall, so make sure to water your lawn and garden appropriately. You can read more about proper watering in these articles:
- “How Often to Water Your Vegetable Garden (And More Watering Tips)”
- “When and How to Water Your Lawn”
Fertilizer and organic material break down into acid or alkaline materials
Fertilizers – especially nitrogen fertilizers – can potentially lower your soil’s pH level. Meanwhile, manure can raise your soil’s pH level. According to the University of California Division of Agriculture and Natural Resources:
- Ammonium-based fertilizers are the most acidifying nitrogen fertilizers.
- Nitrate-based fertilizers are the least acidifying nitrogen fertilizers.
- Animal manure contains calcium and magnesium, which can make your soil more alkaline.
- Compost and potassium fertilizers have little impact on your soil pH.
Soil amendments change your soil pH
Lastly, using soil amendments can change your soil’s pH. They’re most often used to raise or lower soil pH. We’ll cover these in the next two sections.
How to increase your soil pH
To increase your soil pH, you’ll need to use these soil amendments:
- Lime
- Wood ash
- Oyster shell meal
- Eggshells
These products contain calcium and magnesium, which makes your soil more alkaline. Make sure not to over-correct your acidic soil as it’s harder to lower soil pH than it is to raise it.
Lime
This is the most common soil amendment homeowners use to raise their soil’s pH level. There are many types of lime available: dolomite, agricultural, and hydrated.
Dolomite limestone (calcium magnesium carbonate) is an organic liming option but it is generally the slowest-acting liming material. Since it has magnesium, it also can solve magnesium deficiencies. Don’t use this if your soil has high magnesium or else it can stunt plant growth.
Agricultural lime (calcium carbonate) is made from pulverized limestone or chalk. It may also have calcium oxide, magnesium oxide, or magnesium carbonate. Avoid those with magnesium if your soil has high magnesium content already.
Hydrated limestone is burnt lime (also called quicklime) mixed with water. It acts very fast but is very dangerous to use. It can overcorrect your acidic soil and damage plant roots (or you) if used recklessly.
Lime can also come in many forms, which also affects how fast it acts. According to Dr. Md. Rasel Parvej of the Louisiana State University AgCenter, the more finely ground lime is, the faster it raises your soil’s pH level. However, he also says that it’s best to have smaller and larger lime particles so there’s a short and long-term effect on soil acidity.
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Wood ash
Left behind after burning wood, wood ash is high in calcium and potassium. According to the University of Georgia Extension, wood ash had been produced in the U.S. for its potash (for fertilizer) and alkali as far back as the 1700s.
Wood ash is less effective than lime in raising the pH of your soil. It’s not that it doesn’t work; you can actually make your soil more alkaline than intended. You’ll just need about twice the amount of wood ash as lime for it to have the same effect.
To use wood ash, you’ll need to spread a thin layer of it over the desired areas in the winter. Make sure not to include large chunks of charcoal.
Note: Try to prevent wood ash from coming into contact with your plants, especially young seedlings and the roots. Apply it directly to bare soil if possible. Otherwise, be careful not to apply too much to your lawn.
Oyster shell meal
Primarily made of calcium carbonate, finely ground oyster shells are an organic alternative to traditional agricultural lime (aglime). Many studies have found that oyster shell meal is almost as effective as agricultural lime, with one noting that it had a liming equivalence of 65% (compared to aglime’s 75%).
While oyster shells can add sodium to your soil, it’s not in amounts that will cause issues.
Buy oyster shell meal here:
Eggshells
Because eggshells are also chock-full of calcium carbonate, they can be used to raise your soil’s pH level.
According to a study by John D. Holmes and David Rueber, both retired experts at Iowa State University, ground eggshells were actually more effective at turning soil more alkaline over the long term – about 18 months and beyond.
They stress the importance of applying the right amount of ground eggshells. You’ll need about three times more eggshells to raise the soil pH compared to the required amount of agricultural lime.
Note: Wash eggshells before using them to remove bits of egg that can attract pests.
How to decrease your soil pH
In comparison, there are very few soil amendments you can use to lower your soil’s pH level:
- Elemental sulfur
- Aluminum sulfate and iron sulfate
Sulfur is the primary agent that increases soil acidity. However, it’s harder to make soil more acidic than it is to make it more basic, especially if you’re dealing with clay soil.
Like with other soil amendments, you’ll need to work sulfur, aluminum sulfate, and iron sulfate into the soil.
Note: Wash off sulfur that gets on your plants or else it can burn them.
You can also use organic matter and ammonium fertilizers to lower soil pH, but you will need large amounts of them to actually make a difference. They are perfectly fine to use to maintain a lower soil ph, though.
Elemental sulfur
Using elemental sulfur is the slower, but safer and less expensive method of lowering your soil’s pH level.
It works very slowly because bacteria need to break it down into sulfuric acid. It will take about three to six months for your soil’s pH to decrease if you use elemental sulfur. However, you can speed this up by using the finest sulfur – as in, the one with the smallest particle size.
Apply elemental sulfur when it’s warm – around spring – as that is when soil bacteria are most active. Applying sulfur in colder temperatures will make it break down slower.
Moist (but not wet) soil also speeds up sulfur decomposition, so keep your soil watered.
Aluminum sulfate and iron sulfate
If you need to lower your soil pH fast, choose aluminum sulfate or iron sulfate. Aluminum sulfate and iron sulfate don’t need bacteria to lower soil pH. Instead, it uses chemical reactions to acidify soil. It’s also quite easy to dissolve, making the soil more acidic almost instantly.
So, what’s the catch? Aluminum sulfate and iron sulfate are more expensive than elemental sulfur. You’ll also need more of either to lower your soil pH – about 6 times more aluminum sulfate or 8 times more iron sulfate.
FAQs about how to change your soil pH
Can I use peat moss to lower soil pH?
It depends on the type of peat moss. According to Joe Hannan of Iowa State University, only Canadian sphagnum peat moss will acidify soil. This is because only it has a pH level low enough to actually influence soil pH – around 3.0 to 4.5 pH.
Can I use sulfuric acid (battery acid) to lower soil pH?
No, we don’t recommend using sulfuric acid to lower soil pH. While battery acid is very effective and quick, it’s way too dangerous to use. It has a pH level of 0.8, so it’s caustic and corrosive.
Can I use baking soda to raise soil pH?
No, you can’t use baking soda to raise your soil pH. You’ll need a lot of baking soda to make your soil more alkaline, which isn’t good for your soil. Baking soda also has sodium, which can sterilize your soil – nothing will grow in it for years.
Hire a lawn care pro to care for your yard
Correcting soil pH imbalances is just one step toward better yard health. You’ll have to mow your lawn and maintain your garden, among other things.
If you would rather spend your free time with your family, on your hobbies, or just some R&R, Lawn Love has your back. Our local pros can:
Hire a Lawn Love pro today.
Sources:
Sources:
- Clemson University Cooperative Extension Service
- Oklahoma State University Extension
- University of California Division of Agriculture and Natural Resources
- Louisiana State University AgCenter
- University of Georgia Extension
- “Potentials of Unconventional Liming Materials in Reducing Soil Acidity” by Gregory Effiong and Dennis Edem (published in the Scholarly Journal of Food and Nutrition)
- Iowa State University Digital Repository
- Iowa State University Extension and Outreach
Main Photo Credit: Binyamin Mellish | Pexels
