Soil pH Level: Testing - Raising - Lowering
Plants require different levels of soil pH to grow well. Read our article about companion plants and the pH levels, here.
Why is my blueberry bush not growing so well, when everything else is doing fine? The correct soil pH level will have a major effect on your plants, fruits, and vegetables. Test your soil pH level and raise or lower the levels.
- How can I test the soil pH? Soil testing can be done naturally with vinegar and baking soda or with a kit.
- How can I raise the pH level of my soil? With lime, potassium carbonate, wood ashes, baking soda and more.
- How can I lower the pH level of my soil? With organic matter, aluminum sulfate, sulfur, coffee, vinegar and more.
We will go through the details of what is required to test your soil – raise and lower the pH levels.
1. Soil pH Scale
Soil pH scale will tell us how acidic or alkaline our soil is.
|Ultra-acidic||below 3.5 pH|
|Extremely acidic||3.5-4-4 pH|
|Very strongly acidic||4.5-5 pH|
|Strongly acidic||5.1-5.5 pH|
|Moderately acidic||5.6-6 pH|
|Slightly acidic||6.1-6.5 pH|
|Slightly alkaline||7.4-7.8 pH|
|Moderately alkaline||7.9-8.4 pH|
|Strongly alkaline||8.5-9 pH|
|Extremly alkaline||Above 9 pH|
2. What Happens When Soil pH is too High
If the soil is too alkaline or too acid, certain plants won’t grow or will grow poorly, and certain important microorganisms might not be able to thrive. Some plants prefer more alkaline/acid soil, but very rare plants thrive in extremes.
Every vegetable, shrub or tree, grows best in its preferred pH. Just to give an example, tomatoes will grow best in the soil that ranges from 6-6.8 pH (meaning slightly acidic to neutral).
3. Effects of Soil pH on Plant Growth
The level of nutrients will vary, depending on the soil’s pH. Growth of certain beneficial organism might be inhibited in extreme conditions (very acidic or very alkaline).
Very Acidic (3-5 pH)
In the soil that is very acidic 3-5 pH, certain nutrients such as Magnesium, Calcium, Copper, and Potassium, will be washed away faster, because they are highly water-soluble.
The growth of beneficial microorganisms (bacteria) will be inhibited, so there will be less organic material available. At this point, phosphates cannot be absorbed.
Acidic (5.1-6 pH)
If the soil’s pH is from 5.1-6, some plants that thrive in acidic conditions might prosper (plants who don’t like lime). The growth of bacteria is still slightly inhibited.
Slightly Acidic to Neutral (6.1-7 pH)
Soil’s pH ranging from 6.1 to 7 is good for many different plants. There are enough nutrients available for healthy growth. Earthworms and beneficial microorganisms thrive in this soil, making it more fertile.
Alkaline (7.1-9 pH)
Iron, Phosphorous, and Manganese are less available. There is often a lot of lime (some plants can’t tolerate it). Plant growth might be inhibited due to nutrients deficiency.
4. Factors Affecting Soil pH
If there is a lot of rainfall, the pH in acid soil can increase, and the pH of alkaline soil can decrease. If the soil is flooded its pH is often from 6.5-7.2
Nitrogen coming from manure, legumes, organic matter, or natural or artificial fertilizers, will increase acidity. Fertilizing with Nitrogen will speed up the process of overall soil acidification.
Amount of Rainfall
The amount of rainfall will determine the acidity/alkalinity of the soil. Higher rainfall usually means more acidic soil, and low rainfall means more alkaline soil.
Some crops, shrubs or trees, will leave the soil more acidic/alkaline. Often soil becomes more acid after harvesting the crops because bases are removed. It also depends on the crops that we harvest (some remove more bases than others).
Quantity of Calcium, Sodium, Magnesium, and Potassium exchangeable cations, also determines the soil’s pH. Dominant Sodium cations increase soil’s pH more than other cations.
Soil’s pH is affected by CO2 in the air surrounding the soil. If the concentration of CO2 is increased, the pH of the soil is lower and more nutrients become available.
The different organisms that are present in the soil might make the soil more acidic/alkaline. Bacteria feeding on the organic matter will gradually create a more acidic environment with their by-products.
Percent Base Saturation
If the percent base saturation is low, the soil will be acid. If the saturation is from 50 to 90, the soil will be neutral or alkaline.
5. How to Test Soil pH
Soil pH can be tested in many different ways, most common are; soil test kits or pH meters. You can also pay for your soil to be professionally tested by a certified lab for its pH, nutrients and other parameters.
Testing Without a Kit
Baking Soda and Vinegar
It’s possible to roughly test your soil without a kit or a pH meter. This method is not as accurate, but it works most of the time.
- Collect samples of soil from different parts of the garden
- You will need 2 tablespoons of soil in each cup
- Add half a cup of vinegar to your soil sample
- Observe the reaction
- If the sample starts to “fizz” = Alkaline
- Ranging from 7.1 to 8.
If the soil didn’t fizz, use the sample from the same part of the garden, adding a little distilled water to get a more liquid consistency. Add half a cup of baking soda to the mixture. In this case, if it starts to fizz, you have acidic soil, more likely ranging from 5-6 of pH.
How does it work? Combining an acid and an alkaline substance will cause a fizzing reaction. If you mix vinegar with baking soda, you will get a fizzing reaction. If you mix acid soil with baking soda, the same will happen, and vice versa.
There is an option your soil might not react at all. This can mean two things, whether your soil is more or less neutral pH (7), or the alkaline soil simply does not contain enough limestone or a similar substance, to cause a reaction.
However, this method does work for most people, and it’s the easiest and cheapest way to test your soil. If you need more specific results, you might want to additionally test your soil with a kit or a pH meter.
Don’t test your soil in times of flooding or drought, as minimum or excess water will alter your soil’s pH. More rain means more acidic soil, not enough rain might mean more alkaline soil. Other factors to take into consideration are nitrogen fertilizers that will increase soil’s acidity. Try to test your soil in most optimal conditions – average humidity and not after using fertilizers
Soil Testing Kits
Soil test kits are available on the internet and almost every specialized gardening store, they are inexpensive and easy to use. Some kits measure only the pH, while others will also measure the level of potassium, nitrates, etc.
These tests are the most affordable and easy to use, even for beginners, but the accuracy of results can sometimes be somewhat lower and is also related to the proper reading of the test results.
Testing With a Kit
Testing kits can be purchased online or in every specialized garden store. These kits are affordable and easy to use.
- Collect soil samples from your garden
- Mix a cup of soil with some distilled water
- “milkshake” consistency
- Dip your pH testing strip inside this mixture for about 25 seconds
- You can clean any excess of dirt from your strip, by dipping it in distilled water.
- Compare color result with color code
Testing With a pH Meter
Electronic pH meters are more accurate when measuring soil pH. You can read the accurate results straight from the meter’s screen. The cost is relatively low and they are very simple to use.
However, these meters need proper care and maintenance (calibrating, correct storage). Most of the time they only test soil’s pH and no other parameters.
Commercial pH meters have become very affordable, and are very accurate. For as low as 10 dollars, you can buy a pH meter that also measures the amount of moisture and sunlight. Some of them don’t require batteries, others do. The meters who require batteries, usually have a digital screen and will require calibration every once in a while, they also offer self-calibrating versions for as little as 20 dollars.
If you decide to buy a battery-free meter, you will have to do your own readings from its display. With the meters that include batteries, the number will appear on the screen (for example 6.5 pH).
How to Use a pH Meter
- Start with digging a small hole in the soil
- You can do it in different parts of the garden
- The hole has to be from 2-4 inches deep (5-10 cm)
- Break up the soil inside the hole to smaller pieces, removing rocks and other larger objects.
- Fill the hole with distilled water – Don’t want to use spring water or rainwater, as springwater might be slightly alkaline and rainwater slightly acidic, which might alter the results.
- Fill the hole with water.
- Insert the probe of your pH meter into the mud. The tester needs to be properly calibrated.
With a digital tester, you will be able to read the results from the screen. With a battery-free tester, you will have to do your own reading from its display. Now you know the exact pH of your soil on different parts of the garden!
Optionally, you can contact your local laboratory that is in charge of measuring the soil pH, quality and so on. The prices are reasonable, and they can give you more information on your soil if necessary (sometimes you have to pay more for additional readings).
6. Testing your Soil for Nutrients
For healthy growth, your plants need essential nutrients and here is why;
The form of Nitrogen that plants can use, is called Nitrate. Nitrate promotes healthy plant development, assisting with chlorophyll productions.
Potassium makes plants stronger, helps to retain water and it’s crucial in the early stages of plant growth and development. It also helps to control plant diseases and to suppress pests. Potassium also helps the plants to endure more extreme temperatures.
Sulfur helps the plants with forming seeds and disease resistance. It’s also one of the crucial elements of aiding plants in the production of amino acids, vitamins, and enzymes.
Calcium is important in plant metabolism and enhances the plant’s ability to absorb nitrates. It’s a crucial element for healthy cell wall development, which makes plants stronger, helping them to fight disease. It helps to neutralize acidity in the growing environment.
Assists with the root and flower growth and helps the plants to endure environmental stressors.
Magnesium helps with phosphorus absorption and promotes chlorophyll production, giving the plants that healthy green color, helping CO2 absorption. Lacking magnesium, your plants and veggies may look a little pale and anemic.
Soil Nutrients Testing Kit
There are many different kits on the internet that you can purchase to test levels of Potassium, Nitrogen, and Phosphorus in your soil, and the pH. There might be kits that will test for additional elements.
There are different options for testing kits that can be purchased online or in specialized stores. Most of the kits are specialized to test nutrients, but some of them will also test the soil’s pH. These kits come with all the necessary instructions for proper use. You will get little glass vials with liquid and test keys. With the solutions included in the test vials, you will be able to accurately test the levels of Potassium, Nitrogen, and Phosphorus in your soil (and other nutrients), and also the soil’s pH.
You need to mix the soil with the solutions provided inside the vials and reading the levels of a certain nutrient with the help of the key provided. Different manufacturers can provide different instructions that you will have to follow. Most of the tests will also include a chart, telling you what is the optimal level of a certain nutrient, and you will be able to see if certain nutrients are lacking in your soil.
7. How to Lower Soil’s pH Level
There are many ways to alter your soil’s pH. Lowering it means, making it less alkaline and more neutral and acidic. Some of the ways that are natural and eco-friendly, while others include chemicals.
Organic Matter: peat – manure – mulch
Compost, manure, peat and acidic mulch, will lower your soil’s pH gradually. As the organic matter deteriorates, microorganisms will feed on it, creating a more acidic environment with their by-products. If you want to lower your soil’s pH fast, these will not give you instant results.
Organic material has many other benefits such as; added nutrients and improving aeration and drainage of the soil. This won’t help too much if the soil is mostly clay.
With aluminum sulfate, you can lower your soil’s pH very quick. As soon as it dissolves in the soil, it makes it more acid (right away). If you need to lower the soil’s pH very fast, this is definitely one of the best options.
Around 1-1,2 pounds of aluminum sulfate is used for 10 square feet of soil, for one level decrease on the pH scale (for example; from 8-7). Be careful not to excessively use it, as aluminum might accumulate in your soil, causing aluminum toxicity.
Sulfur is often cheaper and stronger than Aluminum sulfate, meaning you can use less, but it lowers the pH slower. Bacteria living in the soil will metabolize it, turning it into sulfuric acid. Different factors determine how fast Sulfur will lower the soil’s pH (temperature, moisture, amount of bacteria).
You will need only 0.2 pounds of Sulfur for 10 square feet of soil, for one level decrease.
Brewed coffee won’t change your pH fast, because its acids are water-soluble. However, it will add some nitrogen to the soil, which will help to reduce pH over a longer period of time, similar to compost or manure.
Freshly ground coffee does have a pH of around 4.5. You can use your freshly ground coffee to reduce soil’s pH, evenly spreading it throughout your soil. For slower effects, you can always use already brewed coffee. This method is best for small gardens, container planting or houseplants.
Just like coffee, vinegar is harmless and eco-friendly, and can be used to efficiently decrease your soil’s pH, not to mention very cheap! Vinegar is very acidic (2.5-3), and can be added directly to the soil, or into the irrigation system.
Make sure you use it in moderation, measuring the pH of the soil every few days, to see if more or less vinegar is needed.
Mix 1 cup of vinegar in 1 gallon of water. Measure the soil’s pH daily until the desired effect. Pour the solution directly into the soil or around growing plants if needed.
Sulfur Coated Urea
Just like sulfur, sulfur-coated urea will work decreasing your soil’s ph over time, but the effects are still faster due to urea (1-2 weeks). It also works as a fertilizer, releasing the nutrients to plants over time.
This is a good choice when soil is very compact and rich in clay. Iron Sulfate will create a chemical reaction to promote more acid soil. It will take from 3-4 weeks to reach full effects. You have to use 10 pounds of Iron Sulfate on 100 square feet, to reduce soil’s pH for one level.
If your soil is very alkaline, you might want to do it 2 times (2 months before planting anything) as it needs 3-4 weeks to work. The iron in this solution can stain your clothing and working areas, so caution is needed.
8. How to Raise the Soil’s pH level
There are few ways to raise the soil’s pH, and most of them are ecologically friendly.
Lime is also known as powdered limestone, and you can find it in almost every garden store. It comes in several forms such as pulverized, pellets and granules, and hydrated. Different forms are useful for different types of soil and levels of moisture.
Pulverized lime comes as finely ground powder and can be easily incorporated into the soil. Granules and pellets can be sprinkled by hand, but might not get as easily incorporated as pulverized lime.
Hydrated lime can be used when the soil is very acidic. It’s water-soluble and works quickly, increasing the soil’s pH. For optimal results, you should apply lime 2-3 months before planting, so there is plenty of time for the pH to change. You can spread it by hand and use a rake or other tools to work it into the soil for optimal effects.
Depending on the type of soil, you will have to use more or less lime to increase the pH level for 1. For more sandy soil 25 pounds/1000 square feet, loamy soil 70 pounds/1000 square feet, and around 100 pounds/1000 square feet is the soil is rich with clay.
Opposed to lime, potassium carbonate is more water-soluble. We can use it with the irrigation system. It works fast in increasing the soil’s pH. If you use potassium carbonate, follow the manufacturer’s instructions found on the packaging.
Tree ash is alkaline and will add nutrients such as potassium, phosphate, and calcium to your soil. It doesn’t work as fast as lime, but it will substantially increase soil’s pH over time. You should always re-measure the soil’s pH every once in a while, to see how the pH has changed.
It works best when mixed with sandy soil. Wood ash will improve soil and plant growth, and is much more beneficial in this aspect, as opposed to Lime. Wood ash can damage seedlings, so don’t add it directly onto young plants.
More information on using wood ashes to benefit your soil: Michigan State University
Baking soda is an eco-friendly way to increase the soil’s pH. The measurement is 1 tablespoon BS/1 gallon of water (mix). Multiply this measurement depending on the size of your garden. Apply to the soil. Measure your soil’s pH, to see if more or less baking soda will be needed.
Baking soda is a cheap and fast way to increase the alkalinity of your soil. The changes in pH can appear as fast as in 24 hours. Remeasure to see the results. It’s gentle to the plants and can be applied even in the growing period.
Oyster – Shell Lime – Eggshells
Oyster shell lime is organic and made of oyster shells. It contains more than 30 % of calcium and can be used to treat calcium deficiency, simultaneously raising the soil’s pH. It’s easily incorporated into the soil and is safe for people and animals (as opposed to hydrated lime, that can be potentially harmful).You will have to use 50 pounds/1000 square feet.
Eggshells are also rich in calcium, and an eco-friendly solution. However, you will need 1-2 pounds for 1 square foot, so they are more appropriate for house plants, small gardens, and container planting.
9. Lowering and Raising Soil pH in Potted Plants
You can use natural ingredients to lower/raise potted plants’ soil pH.
Mix 1 cup of vinegar in 1 gallon of water. This mixture can be applied directly into the potting soil, but start slowly, just watering the plant. Measure the pH in a while to see the results.
The remains of your brewed coffee will gradually decrease the soil’s pH and add some nitrogen to the soil. If you need a higher reduction, add freshly ground coffee beans (not brewed), in small quantities. Don’t add too much, to avoid shocking the plants.
Add it gradually, while monitoring the pH. Houseplants or veggies that love more acid soil and nitrogen, can always benefit from some brewed coffee remains.
To make your houseplant soil richer in calcium and increase the pH, you can add crushed eggshells. Wash the eggshells to remove any yolk and eggwhite, that could rot and smell. Crush them by hand or with kitchen tools. Apply moderately and gradually to plants that need more calcium, or to increase pH.
Baking soda is accessible, eco-friendly, gentle to the soil, and will increase alkalinity fast. Be careful with houseplants, as the amount of soil is much smaller. Add baking soda gradually, in small quantities and with care. The mixture is 1 tablespoon of baking soda/1 gallon of water. Don’t overwater the plants, just water with this mixture when necessary.
The changes in pH can appear as fast as in 24 hours, and the mixture is safe to apply in the growing period.
Lowering & Raising
Overwatering your plants can make the soil more acidic. Not watering enough, will make it more alkaline. If you overwater the plants making the soil more acidic, you don’t have to add baking soda or eggshells, just wait for the soil to dry out and water moderately in the future. If the soil is too dry, water to increase its pH.
10. How to Lower pH in Soil Fast
As mentioned before, Aluminum sulfate will lower your soil’s pH very quick. As soon as it dissolves in the soil, it makes it more acid. Use it in moderation, as aluminum might accumulate in your soil, causing aluminum toxicity. The amount that needs to be added is mentioned above (6.2).
Sulfur coated ureaJust like sulfur, sulfur-coated urea will work decreasing your soil’s ph over time, but the effects are still faster due to urea (1-2 weeks). It also works as a fertilizer, releasing the nutrients to plants over time. The amount that you need to add is mentioned above (6.6).
Opposed to lime, potassium carbonate is more water-soluble. We can use it with the irrigation system. It works fast in increasing the soil’s pH. Follow the manufacturer’s instructions to apply the right amount.
The cheap, eco-friendly way to increase soil’s ph in as little as 24 hours.
11. How to Make Soil Acidic for Blueberries
Blueberries grow best in acid soil. If the soil where you are planting blueberries is from 4.6 to 5.5, this is the perfect pH to grow blueberries. If it’s pH is higher than 6, you will have to make it more acidic. Pine needles and mulch might help a little over a long period of time. Fortunately, there are other solutions.
- Adding vinegar, coffee, or other above-mentioned solutions (depending on how much you need to acidify the soil, you will have to use less (coffee, vinegar) or more (chemical solutions) drastic measures.
- Adding peat moss and decaying leaves to the soil before planting
- Adding plenty of mulch (2-3 inches) around the plants- Enough water will keep the soil level acidic (regularly watering)
12. How Much Sulfur is Needed to Lower Soil pH
Opposed to aluminum sulfate, you won’t require much sulfur to lower your soil’s ph. Sulfur is cheaper and you use smaller amounts. Bacteria living in the soil will metabolize it, turning it into sulfuric acid, so it will take longer than aluminum sulfate to alter the pH. Generally, 0.2 pounds of sulfur is needed to change the pH level for 1, in 10 square feet of soil.
For example, for 20 square feet of soil, you will need 0.4 pounds of sulfur to bring it from 7 to 6.
13. What is The pH Level of Clay Soil?
Since clay soil is composed of different organic materials and has different chemical compositions, the pH of clay soil differs in different geographical areas. Even in the same town, different gardens might have different pH when measuring clay soil. The amount of water in the area and nitrogen fertilizers used will also alter the soil’s pH.
Clay soil is more alkaline by nature, while sandy soil, for example, tends to be acidic. Clay soil might be too alkaline for certain plants, and more likely you will need to alter its pH. If only a small part of your garden is composed mainly of clay, you can find crops that thrive in clay soil (many different flowers).
Green beans, lettuce, chard, broccoli, cabbage, and Brussels sprouts, may grow better in clay, or partially clay soil, due to better moisture retention properties. Adding wood ashes might improve your clay soil texture over time.
More information about clay soil can be found at A Green Hand
14. Preserving and Protecting Nature
When altering soil’s pH, is best to use eco-friendlier options, such as different types of lime, coffee, vinegar, baking soda, wood ash and similar.
Excessively and often using large amounts of chemicals to alter your soil’s pH fast, can create soil’s toxicity and it’s not good for people, animals, plants or the soil. Think and plan before, so you can start early enough to alter your soil’s pH gradually, but with less invasive methods.
The chemicals might alter the pH fast, but might also poison nature and end up in your drinking water. Occasionally, and if really necessary, you can use different chemicals, but try to avoid them if possible, or use them in moderation.