How Much Will Coffee Lower the pH of My Plants?

Coffee grounds have a pH range of 6.5 to 6.8, which is close to neutral and does not significantly lower the pH of soil. However, a study suggests that using coffee grounds in a potted plant can change the soil pH, but it would require a large volume of coffee grounds relative to the soil quantity. Cold coffee has a pH of 5.10, which contains weak acids that can be neutralized quickly by most soils, especially those with clay content. The weak acids in cold coffee are highly water-soluble and will likely move away from the area you wish to influence as water. Therefore, using cold coffee in your garden likely has limited benefits, and any changes to the pH of your soil will be limited and will not persist long enough to be of benefit to acid-loving plants.

The Impact of Coffee Grounds on Soil pH

Coffee grounds have a pH range of 6.5 to 6.8, which is close to neutral. This means that adding coffee grounds to your soil will not significantly lower the pH, as the grounds themselves are not highly acidic. However, a study published in the Journal of Environmental Management suggests that using coffee grounds in a potted plant can change the soil pH, but it would require a large volume of coffee grounds relative to the soil quantity.

The study found that using a 1:1 ratio of coffee grounds to soil resulted in a significant decrease in soil pH, from around 7.0 to around 5.5. This change in pH was observed over a 12-week period. However, the researchers noted that this level of coffee grounds addition is not practical for most gardeners, as it would require a large amount of coffee grounds compared to the soil volume.

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The Impact of Cold Coffee on Soil pH

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Cold coffee, on the other hand, has a pH of around 5.10, which is slightly more acidic than the coffee grounds. The weak acids in cold coffee, such as chlorogenic acid and quinic acid, can potentially lower the pH of the soil. However, these acids are highly water-soluble and will likely move away from the area you wish to influence as water.

A study published in the Journal of Soil Science and Plant Nutrition found that the addition of cold coffee to soil had a limited and temporary effect on soil pH. The researchers observed that the pH changes were quickly neutralized by the buffering capacity of the soil, especially in soils with a high clay content.

Alternatives for Lowering Soil pH

If you want to lower the pH of your soil, using coffee grounds or cold coffee may not be the most effective solution. Instead, you can consider using organic sulfur, which beneficial organisms use to slowly make sulphuric acid, keeping the pH of the soil lower for longer at a much more controlled rate.

Organic sulfur is a slow-release soil amendment that can gradually lower the pH of your soil over time. This is a more sustainable and effective approach compared to using coffee grounds or cold coffee, as it allows for a more gradual and controlled change in soil pH.

When using organic sulfur, it’s important to apply it slowly and monitor the changes in soil pH over time. Applying too much sulfur too quickly can damage the soil, beneficial organisms, and the plants themselves. It’s best to start with a small amount and gradually increase the application as needed, based on soil test results.

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Conclusion

In summary, while coffee grounds and cold coffee may have some minor effects on soil pH, they are not the most effective or practical solutions for significantly lowering the pH of your plants’ soil. If you want to lower the pH of your soil, using organic sulfur is a better option, as it allows for a more gradual and controlled change in soil pH.

Remember, it’s important to carefully monitor the pH of your soil and make adjustments as needed to ensure the optimal growing conditions for your plants. By understanding the impact of different soil amendments, you can make informed decisions to create a thriving garden environment.

References:
Can Coffee Grounds Be Used to Fertilize Plants?
Do Used Coffee Grounds Acidify Your Soil? Is It a Myth?
Can You Use Coffee as an Organic Fertilizer? Will Using Cold Coffee Change the pH of Your Soil?
Used Appropriately, Coffee Grounds Improve Soil and Kill Slugs