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As plant lovers, soil pH is an important factor to be concerned about when taking care of your plants. Soil pH is all about the relative alkalinity or acidity of the soil. Measuring and monitoring pH levels is essential simply because plants need an ideal pH level to absorb the necessary nutrients which allows them to thrive and produce maximum yield.
If you aren’t sure about soil pH levels and what it’s all about, read this beginner’s guide to find out more.
What is Soil pH?
The term pH in soil stands for “potential of hydrogen”. Soil pH is a measure of the acidity or alkalinity of the soil, which is determined by the concentration of hydrogen ions in the soil.
The pH scale ranges from 0 to 14, with pH 7 being neutral. A pH below 7 is considered acidic, while a pH above 7 is considered alkaline. Soil pH can affect the availability of nutrients to plants and the activity of microorganisms in the soil, which can have an impact on plant growth and health. The majority of plants thrive at their best between pH 6.0 – 7.5, but it all depends on the type of plant.
Whether or not you need to increase your soil pH levels depends on the type of plants you want to grow. Some plants prefer alkaline soil, while others require acidic soil. It’s important to test your soil pH before making any adjustments to ensure that you don’t harm your plants.
Let’s take a comprehensive look at factors affecting soil pH and how you can monitor and adjust it to maintain a healthy garden.
How Is the pH Level of Soil Affected?
Parent Material
The parent material in soil pH levels refers to the geological material from which the soil was formed. The type of parent material can have an impact on the soil’s pH levels, as certain types of rock or sediment can be more acidic or alkaline than others.
Soils that are formed from limestone, which is a relatively alkaline material, may have higher pH levels than soils that are formed from granite, which is a more acidic material.
Conditions of the parent material from which the soil was formed is a main factor that can affect the pH of soil.
It’s important to note that other factors such as climate, vegetation, and human activities can also affect soil pH levels
Rainfall
Rain on its own is neutral in pH levels. When rainwater falls through the atmosphere, it picks up pH contaminants such as carbon dioxide and other gases, forming weak carbonic acid. Rainfall leaches alkaline compounds of the soil such as potassium, calcium and magnesium, replacing them with acidic elements which decreases the pH of the soil and makes it more acidicThis way, rainfall can affect soil pH levels by either increasing or decreasing the acidity of the soil.
If the rainfall is high in acid-forming pollutants, such as sulfur dioxide or nitrogen oxides, it can make the soil more acidic. This can be harmful to some plants that require a more neutral or alkaline soil pH.
On the other hand, rainfall can also help to neutralize soil pH levels by washing away acidic elements from the soil. In areas with high rainfall, it’s important to regularly test soil pH levels and make any necessary adjustments to ensure optimal soil conditions for plant growth.
Fertilizers
Fertilizers can affect soil pH levels in different ways. Some fertilizers are acidic and can lower soil pH levels, while others are alkaline and can raise soil pH levels. For example, ammonium-based fertilizers are acidic and can lower soil pH levels, while lime-based fertilizers are alkaline and can raise soil pH levels.
Overuse of fertilizers can also lead to a buildup of salts in the soil, which can affect soil pH levels and reduce the availability of nutrients to plants.
Decomposition of Organic Matter
Organic matter, such as animal or plant debris, can affect soil pH levels helping to stabilize soil pH and prevent it from becoming too acidic or alkaline. When organic matter such as plant debris or animal waste decomposes, it releases organic acids that can lower soil pH levels especially on the topsoil.
Organic matter also releases alkaline substances that can raise soil pH levels, but this also depends on the type and quantity of organic matter present. Soils with high levels of organic matter are more resistant to pH changes and can maintain a more stable pH over time. This can also help improve soil structure and increase the availability of nutrients to plants.
How to Measure Soil pH
There are a few ways to test your soil pH levels at home:
- pH Testing Kit: A pH testing kit can be purchased at most garden centers or online. Follow the instructions on the package to obtain accurate results.
- Digital pH meter: A digital pH meter is an electronic device that measures the pH of soil. They can be found at garden centers or online. Simply insert the meter into the soil and follow the instructions.
- Homemade test: You can make your own pH testing solution by mixing distilled water and vinegar in a 1:1 ratio. Then, collect a small amount of soil and mix it with the solution. If the solution fizzes, the soil is alkaline (pH above 7). If it does not fizz, the soil is acidic (pH below 7). Although this DIY method seems easy and cost effective, it may not be the most accurate.
How to Increase Soil pH
It’s important to note that increasing soil pH should be done carefully and with caution. This is because over-liming can lead to alkaline soil conditions, which can cause nutrient imbalances and negatively impact plant growth. Remember to monitor the soil pH and adjust the amendments only as necessary.
To increase soil pH levels, you can use various soil amendments that contain calcium and magnesium which react with soil acidity and neutralize it. The amount of amendment needed depends on the initial pH of the soil and the desired pH. Here are some amendments you can use.
a) Lime
Lime (calcium carbonate) is the most used soil amendment to raise pH. It reacts with soil acidity and neutralizes it. The amount of lime needed depends on the initial pH of the soil and the desired pH. Consult with a local agricultural extension office to determine the appropriate amount for your specific soil.
b) Wood Ash
Another organic way to increase your soil pH is by sprinkling wood ash over the soil and mixing it into the soil until it is 6 to 8 inches deep. It is ideal to add the wood ash early, before planting for the best results.
Wood ash is a natural byproduct of burning wood. It contains potassium and calcium carbonate, which can be used to raise soil pH. However, it is important to use wood ash sparingly, as too much can cause an imbalance in soil nutrients.
c) Dolomite Lime
Dolomite lime is a natural rock that contains both calcium and magnesium carbonate. It can be used to raise pH in acidic soils and also provides additional magnesium, which is an essential nutrient for plants.
d) Calcium Carbonate
Calcium carbonate is an inexpensive and effective way to raise pH. It can be found in a variety of forms, including crushed limestone, marble chips, and oyster shell flour.
e) Agriculture Lime
Agricultural lime, which is made from pulverized limestone or chalk, is also a commonly used substance. It’s also important to know that it may also contain other chemical compounds such as magnesium carbonate and calcium oxide.
f) Hydrated Limestone
A form of hydrated pulverized limestone, which is one of the fastest methods to increase your soil pH if it can be applied down into the soil instead of just leaving it on the top surface. However, its highly recommended that the user is extremely cautious when dealing with hydrated limestone as it is very easy to overdose the soil. An overdose of soil with hydrated limestone will burn your plant roots and cause serious damage.
g) Oyster Shell Lime
The organic, finely ground oyster shells break down quickly and increase your soil pH. It contains 39% calcium which will also help to correct calcium deficiencies of your soil, aiding you to grow a healthy plant.
h) Eggshells
Eggs are an easy at kitchen by-product. When dried and pulverized eggshells are a great source of calcium which can increase the alkalinity of soil in small quantities. Simply, add 1-2 pounds of shells per square foot.
i) Baking Soda
This kitchen staple ingredient is one of the easiest, fastest and cost-effective ways you can use to reduce your soil pH. Since this substance is gentle and harmless, you can use it whenever required as it does not cause any harm to your plant.
How to Decrease Soil pH
To decrease soil pH levels, you can use various soil amendments such as sulfur, aluminum sulfate, iron sulfate, or elemental sulfur. These amendments increase soil acidity and lower soil pH. The amount of amendment needed depends on the initial pH of the soil and the desired pH.
It’s important to note that decreasing soil pH should be done carefully and with caution, as over-acidification can be harmful to plants and microbes in the soil. It’s best to monitor the soil pH and adjust the amendments as necessary. Additionally, it may take time to see the full effects of soil amendments on soil pH, so it’s important to be patient and continue monitoring the pH levels over time.
Recommended Soil pH Levels for Plants
As different plants require varying ranges of pH levels, below mentioned are some types of plants with their optimum pH range which you can refer to when selecting a plant to grow.
| Name of Plant | Optimum pH range | |
| Flowers | ||
| Alyssum | 6.0-7.5 | |
| Begonia | 5.5-7.0 | |
| Bleeding Heart | 6.0-7.5 | |
| Carnation | 6.0-7.0 | |
| Chrysanthemum | 6.0-7.5 | |
| Coneflower | 5.0-7.5 | |
| Crocus | 6.0-8.0 | |
| Dahlia | 6.0-7.5 | |
| Daffodils | 6.0-6.5 | |
| Daisy | 6.0-8.0 | |
| Delphinium | 6.0-7.5 | |
| Geranium | 6.0-8.0 | |
| Hibiscus | 6.0-8.0 | |
| Marigold | 5.5-7.5 | |
| Poppy | 6.0-7.5 | |
| Rose, rugosa | 6.0-7.0 | |
| Sunflower | 6.0-7.5 | |
| Tulip | 6.0-7.0 | |
| Vegetables | ||
| Asparagus | 6.0-8.0 | |
| Bean | 6.0-7.5 | |
| Beetroots | 6.0-7.5 | |
| Broccoli | 6.0-7.0 | |
| Cabbage | 6.0-7.0 | |
| Carrot | 5.5-7.0 | |
| Celery | 5.8-7.0 | |
| Cucumber | 5.5-7.0 | |
| Garlic | 5.5-8.0 | |
| Lettuce | 6.0-7.0 | |
| Potato | 4.8-6.5 | |
| Pumpkin | 5.5-7.5 | |
| Spinach | 6.0-7.5 | |
| Tomato | 5.5-7.5 |
Frequently Asked Questions on Soil pH Levels
Soil pH is important because it affects the availability of nutrients in the soil. So, maintaining the proper pH range can help ensure that plants have access to the nutrients they need for healthy growth.
You can test your soil pH using a soil pH test kit, which is available at most garden centers and online. You can also send a soil sample to a lab for more accurate testing.
Most plants prefer a slightly acidic to neutral soil pH range, between 6 and 7. Some plants, such as blueberries, prefer a more acidic soil with a pH between 4.5 and 5.5.
If your soil pH is too high, you can lower it by adding soil amendments such as sulfur, aluminum sulfate, or iron sulfate.
If your soil pH is too low, you can raise it by adding soil amendments such as lime, wood ash, or dolomite lime. It’s important to adjust the soil pH slowly and carefully, as sudden changes can harm plants and soil microbes. It’s also important to test your soil pH regularly and adjust the amendments as needed.
Yes, soil pH can affect soil structure. Soil that is too acidic or alkaline can reduce the ability of soil particles to stick together, which can lead to poor soil structure and drainage problems.
Yes, soil pH can affect the types of plants that can grow in a garden. Some plants prefer acidic soil, while others prefer alkaline soil. If the soil pH is not suitable for the plants you want to grow, they may not grow well or may even die.
Yes, soil pH can vary in different parts of a garden. Factors such as soil type, drainage, and nearby plants can all affect soil pH.
It’s a good idea to test your soil pH at least once a year, preferably in the spring before planting. However, if you are experiencing problems with plant growth, you may want to test the soil pH more frequently to see if that is the cause.
Wrapping Up
An optimum pH is key for the successful growth of any plant. Like other important factors such as water, temperature, and light, maintaining the ideal pH of the soil also does play a major role in helping your plant to thrive and be healthy.
To provide the best conditions for your plant, you can start off by simply running a soil test, measuring the current pH and understanding what your plant needs. Use the information about soil pH levels in this beginner’s guide to help you keep your plants happy and thriving!
