Compost is typically slightly acidic, with a pH level ranging from 6.0 to 6.8. It is a natural fertilizer made from decomposed organic materials, such as kitchen scraps and yard waste, which undergo a process called composting.
Composting involves the breakdown of these materials by bacteria, fungi, and other microorganisms. During this process, organic matter decomposes and releases various compounds, including organic acids, which contribute to the slightly acidic nature of compost.
Despite its acidity, compost is beneficial for plants and soil as it improves soil structure, nutrient availability, and microbial activity, promoting healthy plant growth.
Does Compost Make The Soil Acidic?
The question of whether compost makes the soil acidic is a common one in gardening and agriculture. In reality, compost doesn’t significantly acidify the soil. Compost can vary in its pH level, being slightly alkaline or slightly acidic. It has the potential to balance pH values rather than push them towards acidity.
When applied, finished compost can naturally raise the pH level in acidic soil, making it less acidic, while in alkaline soil, it can lower the pH level, reducing alkalinity.
Additionally, compost can be a valuable source of essential nutrients for plants. In the case of alkaline soil, compost can supply the nutrients that may be lacking, further illustrating its ability to enhance soil quality.
So, while compost may have a slightly acidic or alkaline influence, it generally works to maintain a balanced and optimal pH level in the soil, making it suitable for a wide range of plants and crops.
What pH is Potting Compost?
The pH of mature compost is generally between 6 and 8. However, the pH of compost changes as it decays. The pH of potting compost can also vary depending on the ingredients used.
For example, MCR Potting Soil Complete has a pH of about 6.5, while Big Rootz Soil has a pH of 6.5 to 6.8 and Fox Farm Ocean Forest has a pH of 6.3 to 6.8. It is important to check the pH of your potting compost before using it, as plants prefer a specific pH range.
If the pH is too high or too low, it can affect the growth of your plants. You can adjust the pH of your potting compost by adding lime or sulfur.
How Is a Compost Acidic?
Compost can be acidic due to the decomposition process, but it can also become neutral or even slightly alkaline. The pH level of compost depends on the materials used and the composting conditions.
pH Scale And Acidity Levels
The pH scale is used to measure the acidity or alkalinity of a substance, with values ranging from 0 to 14. A pH of 7 indicates neutrality, values below 7 are considered acidic, and values above 7 are alkaline.
When it comes to compost, the pH level can vary depending on several factors.
Here are some key points to consider:
Compost pH:
Compost is generally slightly acidic, with a pH ranging from 5.5 to 7.5. This level is beneficial for most plants as it promotes nutrient availability and microbial activity.
However, it’s important to note that pH levels can vary depending on the materials used in the composting process and the environmental conditions.
Acidic compost:
In some cases, compost can become more acidic due to factors such as excessive use of acidic materials like pine needles, coffee grounds, or fruit waste.
Acidic compost can have a pH below 5.5, which may affect certain plants that prefer neutral or alkaline conditions. It’s important to monitor the pH levels of your compost and adjust if necessary.
Alkaline compost:
On the other hand, compost can also become alkaline if there is an excess of alkaline materials like wood ashes or lime. Alkaline compost may have a pH above 7.5, which can impact the availability of certain nutrients.
Influences On Compost Acidity
The acidity of compost can be influenced by various factors, including
Feedstock materials:
The types of organic materials used in composting can significantly impact compost acidity. Materials like citrus peels, coffee grounds, and pine needles tend to be acidic, while materials like wood ash and eggshells can be alkaline.
Balancing the mix of acidic and alkaline materials is crucial to maintaining a neutral to slightly acidic pH range.
Decomposition process:
The decomposition process itself can affect compost acidity. Microorganisms involved in the decomposition process produce organic acids, which contribute to the overall acidity of compost.
Factors such as temperature, moisture levels, and oxygen availability can influence microbial activity and consequently, compost acidity.
Environmental conditions:
Environmental factors like rainfall, temperature, and soil composition can also influence compost acidity.
Heavy rainfall or exposure to acidic soil can lead to the leaching of acidic compounds into the compost, affecting its pH levels.
Similarly, alkaline soil conditions can result in alkaline compost.
Factors Affecting Compost Ph: Several factors can affect the pH of compost, including:
| Factor | Influence on Compost pH |
| Water Quality | The pH of the water used can affect the compost’s pH. |
| Microbial Activity | Microorganisms thrive in specific pH conditions, influencing compost pH. |
| Aeration | Inadequate aeration can lead to acidic conditions. |
| Composting System | Different systems have unique requirements for pH control. |
Useful Ph Levels For Different Plants
Compost is known to have a varying pH level, but it often leans toward being acidic. It is important to consider this acidity when using compost for different plants, as some plants thrive in acidic conditions while others prefer neutral or alkaline pH levels.
Acid-Loving Plants:
Acid-loving plants thrive in soil with a pH below 7.0.
These plants prefer an acidic environment, as it allows them to access essential nutrients more easily.
Some common acid-loving plants include blueberries, azaleas, rhododendrons, and hydrangeas.
Soil pH levels of around 4.5 to 6.0 are ideal for these plants.
Acidic soil helps these plants absorb nutrients such as iron, manganese, and phosphorous more effectively.
To maintain the optimal pH level, you can add organic matter like compost or peat moss to the soil.
Neutral-Loving Plants:
Neutral-loving plants can thrive in soil with a pH of 7.0.
These plants are relatively adaptable and can tolerate a wider pH range compared to acid or alkaline-loving plants.
Some examples of neutral-loving plants include tomatoes, beans, lettuce, and marigolds.
Soil pH levels ranging from 6.0 to 7.0 provide an ideal growing condition for these plants.
Neutral pH allows for the proper uptake of nutrients such as nitrogen, potassium, and phosphorous.
Regularly testing the pH level of the soil and making adjustments as needed can ensure optimal growth for these plants.
Alkaline-Loving Plants:
Alkaline-loving plants prefer a soil pH above 7.0.
These plants are well-suited to alkaline soil conditions, as it provides them with the necessary nutrients.
Common alkaline-loving plants include lilacs, asparagus, lavender, and clematis.
Soil pH levels ranging from 7.0 to 8.5 are ideal for their growth.
Alkaline soil facilitates the absorption of nutrients like calcium, potassium, and magnesium.
To create an alkaline environment, you can add substances like wood ash or limestone to the soil.
Frequently Asked Questions Of Is Compost Acidic
Does Compost Make Soil More Acidic?
Compost can have a slight effect on soil pH, potentially making it more acidic. This change is generally minimal and varies depending on the composition of the compost and the initial pH of the soil.
The decomposition process in compost may release organic acids, which could lower pH levels.
However, the impact is typically not significant, and compost is still considered an excellent soil amendment for improving overall soil quality and fertility.
What Is the pH of Compost?
Compost typically falls within a pH range of 6 to 8, making it slightly acidic to moderately alkaline. This neutral to slightly alkaline pH range renders compost suitable for a wide variety of plants.
It means that when you add compost to your soil, it can have a balancing effect, helping to maintain a healthy pH level that’s conducive to plant growth.
Is Bagged Compost Acidic?
The pH of bagged compost may vary depending on the source and production methods. However, in most cases, bagged compost tends to have a pH that is neutral to slightly acidic.
It’s important to check the specific product label or consult the manufacturer’s information to understand the pH level of the bagged compost you’re using.
How Do I Make My Compost Alkaline?
If you wish to make your compost more alkaline, you can do so by incorporating alkaline materials like wood ashes or crushed eggshells. These materials can raise the pH level of your compost.
However, it’s essential to exercise caution when adjusting pH, as excessive alkalinity can have adverse effects on plant growth.
Always monitor pH levels and adjust incrementally to ensure a healthy balance for your plants.
Conclusion
To sum up, compost can have varying levels of acidity depending on the specific materials used and the composting process. It is generally recommended for compost to be slightly acidic, as this promotes the breakdown of organic matter and facilitates nutrient absorption by plants.
However, it is important to monitor the pH level of compost to ensure it does not become too acidic, as this can inhibit plant growth. Adding alkaline materials such as limestone can help balance the acidity of compost if necessary.
Overall, understanding the acidity of compost is crucial for gardeners and compost enthusiasts alike, as it directly impacts the health and productivity of plants.
Reference:
https://www.originalorganics.co.uk/blog/how-to-make-great-leafmould#
https://forum.gardenersworld.com/discussion/1045255/ph-levels-and-manure-compost
I am a graduate of Bangladesh Agricultural University, where I delved into various agricultural disciplines, equipping me with a profound understanding of agriculture. Beyond academics, I have hands-on experience in gardening and crop cultivation. My passion is to embrace sustainable farming and horticulture. With a BSc in Agriculture, I am dedicated to promoting environmentally conscious and efficient agrarian practices.
Bachelor of Science (BSc) in Agriculture (Hons.)
Master of Science. (Sustainable Agriculture & Food Security ) (MS)
Bangladesh Agricultural University
